AUTOMOTIVE DICTIONARY

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AUTOMOTIVE DEFINITIONS
4X2
Used to describe a vehicle with two-wheel drive. The first figure is the number of wheels, and the second is the number of powered wheels. Another term for two-wheel drive.
4X4
Used to describe a vehicle with four-wheel drive. The first figure is the number of wheels, and the second is the number of powered wheels.
A-pillar
Vertical roof support between the windshield and front edge of the front side window.
AARA
The American Auto Racing Association, located in Spokane, Washington.
ADRA
American Drag Racing Association, located in Spokane, Washington.
AHRA
American Hot Rod Association
AMS
Atlanta Motor Speedway
ARCA
Automobile Racing Club of America, the little brother to the Winston Cup racing (ARCA is two levels below). ARCA sports similar cars with shorter races and small pay-outs.
Accumulator
Removes moisture from the liquid refrigerant in an air-conditioning system.
Active Body Control
The active suspension system Active Body Control, developed by Mercedes-Benz, resolves the traditional conflict between active safety, responsive handling and ride comfort and is thus an important landmark in passenger car design. Using high-pressure hydraulic servos, an ingenious sensor system and high-performance microprocessors, ABC adapts the suspension and damping to different driving situations. The computer-controlled hydraulic servos or "plungers", which are mounted in the spring struts between the coil springs and the body, develop additional forces which act on the suspension and damping to control body motion. ABC is designed to control body vibrations in the frequency range up to 5 Hz - the kind of vibrations typically caused by uneven road surfaces or by braking and cornering. To control the higher-frequency wheel vibrations, passive gas-pressure shock absorbers and coil springs are used, which can be tuned for high ride quality. ABC virtually eliminates body movements when moving off from rest, when cornering and when braking. Cornering roll on S-Class models equipped with ABC is significantly reduced and there are also safety advantages in high-speed evasive manoeuvres compared with cars with conventional suspension systems. A press of a button on the centre console allows drivers to choose between comfortable or sporty suspension settings.
Active Suspension Systems
Active suspension systems move each wheel up and down to control body motion in response to road abnormalities. The system responds to inputs from the road and the driver. With an active suspension, a vehicle can simultaneously provide the smooth ride of a soft suspension along with superior handling associated with a firm suspension.
Most active suspension systems use a high-pressure pump with hydraulic cylinders at each wheel to position the wheels with respect to the vehicle. Up and down motion of the wheels is actuated by electronically controlled valves. Other alternatives to power active suspension systems include electric motors or electromagnets. In any system, sensors at each wheel determine vertical wheel position and the force of the road acting on the wheel. Some systems use "road preview" sensors (radar or laser) to provide information about road abnormalities before the front wheels reach them. Accelerometers tell the computer when the vehicle is accelerating, braking or cornering. The computer uses complex algorithms to continuously process information and decide the position of each wheel. Coil springs can be used at each wheel to avoid "bottoming out" of the suspension in case of system failure; they also can reduce the power required to support the sprung weight of the vehicle.
Active Tilt Control
Active tilt control winds up the stabilizer bars in the front and rear suspension to resist body lean while cornering. Because active control is used only as needed, vehicle spring rates and stabilizer bar stiffness can be reduced, improving normal ride characteristics. In addition, this system has potential to increase low-speed, off-road traction on 4WD vehicles.
The control module receives a lateral acceleration signal from a body-mounted accelerometer. The module directs pressure from a pump to hydraulic cylinders that replace stabilizer bar links. During cornering, the cylinders wind up the stabilizer bars, which increases resistance to body lean. The system is deactivated at slow speeds to increase driver comfort. Off-road traction is improved due to lower resistance from the stabilizer bars, allowing the front and rear wheels to better follow the surface of rough roads.
Actively Ventilated Seats
Leather-trimmed actively ventilated high-comfort seats are optionally available for the S-Class. Built into the seat cushions and backrest are a number of small fans, which draw in air from underneath the seat. Even if extreme heat has built up inside the car, this air will be perceived as agreeable in temperature because it is slightly below the normal temperature of the skin. The air is distributed evenly across the entire surface of the seat via plastic ducts, an air-permeable fabric and fine perforations in the leather, in this way continuously transferring perspiration moisture away from the passengers. Active seat ventilation can be activated by pressing a button in the door panel. This initially engages the highest of three different speeds, or stages. Three blue LEDs above the switch indicate the currently engaged speed. In order to prevent chilling, the ventilation automatically switches from stage three to stage two after approximately ten minutes, then after a further ten minutes switches to stage one.
Actuator
A device that performs a mechanical action in response to an input signal, which may be electrical or fluidic.
Adaptive Cruise Control (ACC)
Adaptive cruise control (ACC) improves on traditional cruise control by allowing a vehicle to automatically adapt to the speed of highway traffic. follow another vehicle at a set distance. With ACC, the driver selects a desired interval to follow traffic as well as the desired cruise speed. When slower traffic is encountered the ACC alters vehicle speed to maintain the desired interval while following traffic. Speed is controlled by ACC with moderate braking when needed. When traffic clears, ACC resumes the desired cruise speed. The driver may override the system by braking at any time.
When activated by the driver, a microwave radar unit or laser transceiver on the front of the vehicle determines the distance and relative speed of any vehicle which may be in the path of travel. The ACC computer continually commands the throttle and brakes to maintain cruise speed or adapted speed of traffic. Braking by the driver can override the system at any time.
Increased driver convenience regarding speed control and improved traffic flow on busy highways.
Adaptive Damping System (ADS)
The standard-specification AIRMATIC suspension system of the Mercedes S-Class combines pneumatic suspension with an Adaptive Damping System (ADS), which adjusts the front and rear shock absorber forces to the current payload, the condition of the road surface and driving style.
A steering angle sensor, three acceleration sensors on the car body, the ABS speed sensor and the brake pedal sensor constantly measure the lateral and longitudinal acceleration of the body. From this data, the ADS control unit calculates the optimal damper setting for each individual wheel and transmits the relevant signals with split-second speed to special valves on the gas-pressure shock absorbers.
These valves are able to switch between four different damping characteristics. Using a selector on the instrument panel, the driver can also switch between a standard mode or a tauter, more sporty mode. This adjusts the thresholds at which the different damping characteristics are activated. In sporty mode, the firmest characteristic is selected earlier, while in comfort mode the softest characteristic remains activated for longer.
Adaptive Transmission Control (ATC)
The Adaptive Transmission Control system recognizes individual styles of driving (e.g., aggressive vs. Relaxed) and adapts transmission shift parameters accordingly. Two types of ATC are adaptive shift-scheduling and adaptive shift-quality control. Adaptive shift scheduling uses information to assess driving style and decides when to upshift or downshift. It also can identify uphill or downhill gradients and recognize hard cornering. This helps inhibit shifts that might be annoying to the driver or affect vehicle stability. Adaptive shift-quality control uses information about the vehicle or environment, such as changes in the transmission due to wear, to improve the quality of shifts. This system can also adjust shift smoothness to suit driving style (e.g., crisper shifts for aggressive driving or smoother shifts for normal driving).
Adaptive Shift Scheduling uses a microprocessor to read signals from various sensors. It uses a complex algorithm and ongoing memory to decide when to shift. For example, high lateral acceleration during cornering may prevent shifting even if the accelerator is suddenly depressed or released. This helps avoid potential loss of tire grip due to load reversal. Shift points can be based on calibration curves in memory. Adaptive shift-quality control adjusts parameters that affect the speed and smoothness of the shift by interpreting data, including driveline feedback from various sensors, as well as post shift parameters.
Improves shift consistency and transmission durability and allows for shifting that is better suited to specific driver styles or operating conditions.
Aerodynamics
The wind resistance of a vehicle's design elements. Aerodynamic vehicles claim to offer increased performance and reduced wind noise while moving. See Coefficient of Drag.
Air Brake
Brakes, usually on heavy-duty trucks, that use compressed air to operate.
Airbag
Safety device using an inflatable cushion that inflates and deflates within a fraction of a second to protect a vehicle occupant.
Airbag Lockout Switch
A device allowing the driver to turn off the front passenger airbag.
Airmatic
Instead of a conventional suspension and damping system with coil springs and gas-pressure shock absorbers, the new Mercedes S-class is equipped with AIRMATIC, a system which combines pneumatic suspension with the Adaptive Damping System (ADS) to ensure a uniformly comfortable ride and high standards of active safety.
AIRMATIC comprises a variety of components which are connected via pneumatic lines and CAN databus (Controller Area Network), namely pneumatic suspension struts front and rear, an air compressor, a central reservoir, air suspension valves, a control unit and various sensors.
AIRMATIC is an open system in which the vehicle weight is supported by the compressed air enclosed in the rubber bellows of the suspension struts. Level control is effected by supplying or releasing air as and when required at each individual wheel, by means of fast-acting solenoid valves. The necessary data for controlling the valves is supplied by two yaw sensors on the front axle and one on the rear axle, which monitor the level of the vehicle.
The air suspension of the S-class not only automatically compensates for different pay-loads but also enables the vehicle level to be raised manually by 25 millimetres at the touch of a button on the instrument panel. This function is particularly useful when driving over dirt tracks, or badly potholed roads.
Alignment
The proper adjustment of the car's suspension. Generally refers to the wheel alignment.
All-Season Tires
Tires designed to provide good traction in winter snow and slush without wearing too quickly on dry roads.
All-Terrain Vehicle (ATV)
A small, lightweight vehicle designed for recreational off-highway use.
Alloy Wheels
Any non-steel road wheel. Mostly aluminum, but technically a mixture of two or more metals.
Alternative Fuels
May be alcohol-based, such as ethanol or methanol; compressed natural gas; or combinations of gasoline and alcohol.
Alternator
Produces alternating current and recharges the battery.
Amortization
The gradual reduction of a debt by periodic payments large enough to meet current interest payments and repay the principal.
Anti-lock Braking System (ABS)
This braking system senses any significant difference in wheel speed, from one wheel to another, when a vehicle is braking hard. When any of the wheels begin to lock up (completely stop rotating) while other wheels are rolling, ABS automatically reduces the braking forces to that "locked" wheel or wheels in order to keep all the wheels rolling - to prevent brake-induced skidding.
ABS can control all four wheels (most cars and SUVs have this system) or only two (this is found on some pickup trucks and SUVs). The system can group wheels together in "channels" of operation (i.e. a three-channel system on a four-wheeled vehicle)or have one channel for each wheel. (four-channel ABS).
Four-wheel, four-channel anti-lock braking system (ABS):
The ABS system prevents the vehicle's wheels from locking during hard braking situations and helps drivers maintain the ability to steer the vehicle where they want it to go. The vehicles' automatically engaging loose-surface program helps shorten stopping distances from speeds of less than 18 mph when the transfer case is in low range.
Anti-Roll Bar
A suspension component. A steel rod or tube that connects the left and right suspension members to resist roll or swaying of the vehicle. Improves handling.
Antifreeze
A liquid that mixes with the water in a cooling system of a vehicle's engine. Antifreeze keeps the water from freezing in the winter or cold climates, or from overheating in the summer or hot climates.
Aspect Ratio
The ratio between the width and sidewall (or height) of the tire. Tires with lower aspect ratios, usually found on sports models, provide superior handling but a harsher ride.
Automatic Locking Retractor
Standard on 1995 and later models, this device is built into the shoulder belt retractor and keeps the belt cinched tightly, which is essential for properly securing a child-safety seat.
Automatic Stick Shift
Select Shift Manual (SSM) and Auto Shift Manual (ASM) use a combination of Auto-Clutch and Shift-By-Wire electronic control system technology to provide the customer a fun-to-shift experience along with significant fuel economy improvements over a base manual transmission. The Select Shift Manual mode allows a customer to command gear changes according to his/her personal preference like a conventional manual transmission. The Auto Shift Manual mode provides the customer automatic gear shifting much like an automatic transmission.
Both the Auto-Clutch subsystem and Shift-By-Wire subsystem use an electro-hydraulic or electro-mechanical actuation system controlled by a stand-alone transmission control module. A customer requests a gear shift by using the appropriate driver interface mechanism (shift lever, push buttons, etc.).
In place of the usual cable/linkage (which is eliminated), a sensor informs the controller of the requested gear shift. The controller processes the request and commands the actuators to open/close the clutch and disengage/engage the gear sequence with very fast response times. Engine torque is controlled during the shift either by controlling the throttle directly (Drive-By-Wire) or enabling ignition/fuel injection control to provide smooth shifts.
Fuel economy improvement with fun-to-shift convenience and shift mode flexibility.
Automatic Temperature Control (ATC)
Automatically controls a vehicle's heating and cooling systems, maintaining a temperature preset by the occupant.
Automatic Transmission
A system that varies the power and torque to a drivetrain without the use of a foot-operated clutch.
Axle
A rotating metal shaft connected to the wheels on either side of the vehicle.
Axle Articulation
This term describes the ability of one axle to move vertically relative to the chassis or its fellow axle - left wheel up, right wheel down (or vice-versa). It is the measure of the ease with which wheels stay in contact with the ground (and retain traction) on a very bumpy uneven trail.
Axle Ratio
The ratio is the relationship between a vehicle's driveshaft (or propellor shaft) and its wheel axle. For instance, a 4:1 axle ration means the drive shaft turns 4 times for every one time the tires spin. The higher numerically the axle ratio, the greater force that can be applied to the drive wheels for tasks like towing up a grade or pulling a boat out of the water. (See also Final-Drive Ratio By changing a vehicle's axle ratio, you may change its towing capacity.
B-pillar
Vertical metal roof support between front and rear side windows on the side of the vehicle.
Balls to the Wall
The phrase "balls to the wall", meaning an all-out effort, sounds as if it is a reference to a part of the male anatomy, giving rise to some confusion as to what it originally meant. However, the original usage has nothing to do with anatomy, coming rather from the world of aviation.
On an airplane, the handles controlling the throttle and the fuel mixture are often topped with ball-shaped grips, referred to by pilots as (what else?) "balls". Pushing the balls forward, close to the front wall of the cockpit results in the most and richest mixture of fuel going to the engines and the highest possible speed.
The phrase dates to the early 1950s. Several veterans have written me noting their use of the term during the Korean War era.
Base-Coat
A coat of paint acting as the base for other layers to be applied.
Beater
(Slang) A car for everyday transportation. Usually not in perfect condition.
Belt Force Limiters
Mercedes-Benz equips the S-Class with belt tensioners on the front seats and outer rear seats which in conjunction with the belt force limiters and airbags significantly reduce the forces acting on the occupants' chest. The belt force limiter is located inside the inertia reel and consists of a torsion bar which turns slowly when a force exceeding a pre-determined level acts on the belt strap, thereby producing a controlled reduction in the locking effect of the inertia reel. From a pre-specified point, the inertia-reel seatbelt slackens and the force exerted by the belt strap on the occupant is reduced.
Beltline
A horizontal line, usually imaginary but sometimes indicated by a feature in the body design, just below the window openings on a car or truck body.
Bench Seats
Full-length seat that can usually seat two or three people.
Bi-xenon Headlamps
Xenon headlamps use xenon gas and metallic salts to create light. An electrically generated arc replaces the filament used in conventional light bulbs. The start-up voltage of up to 28,000 V is supplied by an electronic ballast module fitted on the headlamp housings. This technology produces twice the light output of a halogen bulb, has five times the lifespan and consumes 30 per cent less power.
This results in much more effective and brighter illumination of the road and road margins, while using only 35 watts. Bi-xenon headlamps are a xenon headlamp which uses a single xenon lamp to produce both the high beam and the low beam. The full light beam is used to produce the high beam, while the low beam is produced by moving a shutter between the bulb and the lens, thus blocking off a portion of the light. The bi-xenon headlamp option for the S-Class (standard on the S 600) also incorporates dynamic range adjustment, which automatically varies the pitch of the headlamps in accordance with the movements of the body and which also compensates for brake dive and squat.
Body Style
The type of exterior shell or shape to a vehicle (sedan, coupe, truck, etc.).
Booster Seat
This child-safety seat is designed for children who are too large for a baby seat, but not big enough to sit safely in the vehicle's seats.
Bore
Diameter of an individual engine cylinder.
Borg Warner Trophy
Victory in the Indianapolis 500 secures this, the most coveted trophy in Indy Car racing.
Box-Section Frame
This term refers to the structure of a frame when viewed in cross section. A Box-section frame is constructed using four sides of steel to create a box, as opposed to a C-section or even I-section frame (which would look like those letters in cross section).
Boxer Engine
The cylinders are opposite (180 degrees apart) from each other. Also called flat engines, these are relatively flat compared to In-line or V engines.
Brakes
Be sure to have your brakes maintenanced on a regular basis. Your brake system is comprised of several components including brake lines, master cylinder, slave cylinders, brake pads, rotors, calipers, and drums. All of these need regular maintenance to ensure that you vehicle will function properly on the road. If your pads are worn, have them replaced.
Check your brake fluid level frequently. The brake warning system has been required standard equipment since 1970. It monitors the differences in pressure in the brake lines of the two hydraulic sub-systems of the master cylinder and alerts the driver with a light when an imbalance occurs.
Brake Assist
This technology senses emergency braking by detecting the speed at which the driver presses the brake pedal and immediately applying all available power boost. Brake Assist can potentially reduce overall stopping distance by eliminating the delay caused by a common human tendency of not braking hard enough or soon enough. Of course, in actual driving situations, braking effectiveness also depends on proper brake system maintenance and tire and road conditions.
The system developed by Mercedes-Benz to shorten emergency stopping distances takes over if a driver applies the brakes quickly but too gently in a critical situation. The system automatically develops maximum brake boost with split-second speed, so reducing the stopping distance by a significant margin.
Tests provide impressive proof of the effectiveness of Brake Assist: on a dry road, most drivers need up to 73 meters for an emergency stop at 100 km/h, since they apply the brakes too gently. With Brake Assist, the car can be brought to a standstill after just 40 meters, a reduction of 45 per cent.
Brake Booster
Device or system that helps reduce the force the driver must exert against the brake pedal. May be hydraulic or electric.
Brake Caliper
A hydraulic (liquid-pressured) piston assembly that holds disc-brake pads.
Brake Drum
The large circular surface that the brake shoe presses against to stop the vehicle.
Brake Fade
As brakes heat up with hard or repeated use, their effectiveness usually diminishes. This is called brake fade.
Brake Lockup
In braking, lockup describes the point at which a tire starts to skid (stops rotating whice the vehicle is in motion) in an emergency stopping situation. A tire's maximum braking force is developed when it is on the verge of lockup, so a car's shortest stopping distances are produced when its front and rear tires are held just short of lockup, giving the advantage of simultaneous steering and braking ability - a locked wheel cannot be steered.
Brake Pad
Used in a disc system, it is a replaceable piece of backing plate and additional friction lining.
Brake Pull
Occurs when the vehicle pulls suddenly to the left or right as the brake pedal is depressed. It indicates the brakes may be out of adjustment.
Brake Rotor
Shiny metal disk that brake pads squeeze to stop the vehicle; hence the name disc brakes.
Brake Shoe
A curved, replaceable piece of friction material used on drum brakes. The wheel cylinder pushes the brake shoes against the brake drum.
Bucket Seats
Individual driver or passenger seats.
Busch Series
Just one level below Winston Cup, some drivers race at both this and Winston Cup level. These races, often run the day before a Winston Cup race, have gained popularity and are now all televised live, nationally.
C-pillar
The vertical metal roof support between the side edge of the rear windshield (also called the backlight) and the rear edge of the rear window.
CAM
The Championship Association of Mechanics, established in 1989, is a non-profit organization that serves the needs of Indy Car crew members. It also acts to publicize their efforts.
CMS
Charlotte Motor Speedway, home of the World 600 Winston Cup Race, now known as the Coca-Cola 600. This is a NASCAR event, also held on Memorial Day.
Camber
Inward or outward tilt of the wheels and tires. This adjustment affects how the vehicle holds the road and handles cornering.
Camshaft
A machined shaft with lobes that open and close engine-cylinder intake and exhaust valves. As the shaft rotates, the lobes push against valve springs to open the valves and rotate away to close them. Driven by the crankshaft.
Carburetor
Device that mixes air with fuel, delivering the mixture into the engine's combustion chambers. Only found on older vehicles. By the mid-1980s, new emissions standards led to the use of fuel-injection systems, which do not require frequent adjustment.
Catalytic Converter
An emissions-control device that removes unburned fuel from the exhaust by burning it.
Center Differential
Rear-wheel-drive cars need a rear differential to power the right and left rear wheels and let them turn at different rates of speed when cornering. Front-wheel-drive cars need a front differential for teh same reasons. Vehicles with full-time or permanenet four-wheel-drive, or with all-wheel drive, require a center differential (or similar device, such as a viscous coupling unit or VCU). In a tight turn, all four wheels travel at different speeds.
A center differential receives power (or more correctly, torque) from the transmission (or transfer box) and sends this torque to the front and rear differentials, while allowing the front and rear wheels to travel at different rates.
Center High-Mounted Stop Light (CHMSL)
NHTSA-required brake light mounted higher than the taillights, at the top center or bottom center of the rear windshield.
Center of Gravity
The point of the car where, if it is suspended, it would balance front and rear.
Center-Locking Differential
On all-wheel drive vehicles, a third differential in addition to those for the front and rear axles. This third differential allows the front and rear wheels to turn at different speeds as needed for cornering on dry pavement. On slippery surfaces, it locks all four wheels together, either automatically or manually depending on the system, for greater traction.
Central Locking System
On a vehicle with power door locks, the system locks or unlocks all doors at one time.
Chassis
This term describes a vehicle's structural elements (or sometimes, more loosely, the collection of components attached to its frame). In vehicles with unitized or "unibody" construction, the chassis comprises everything but the bolted-on body panels of the car. In vehicles with a separate frame, chassis usually refers to the frame.
Chlorofluorocarbons (CFCs)
Chemicals formerly used as refrigerants in cooling systems. No longer used because they are considered harmful to the Earth's ozone layer.
Christmas Tree
The pole of lights that starts a drag race, named for its red and green lights. Most drag races use the pro or heads up start which has three lights in between the first (red) and last (green) stage.
Clearcoat
The transparent top coat of paint on many newer vehicles; designed to create a long-lasting, lustrous appearance.
Climate-Control System
The non-technical term for the heating, ventilation and air-conditioning system (HVAC). Most current vehicles have all three -- heating, defrost and AC.
Clutch
Device that connects or disconnects the engine from the transmission.
Clutch Disk
Presses against the the transmission flywheel to transfer power from the engine to the transmission.
Coefficient of Drag (Cd)
A measure of the aerodynamic resistance of the vehicle body. The smaller the number, the more wind-cheating the body design and the greater likelihood that passengers won't have to endure wind noises.
Coil Spring
A suspension component made up of spiral-wound hardened steel, used to isolate a vehicle from the up-and-down movement of the wheels on the road.
Combustion Chamber
Top section of the engine cylinder, where the air-fuel mixture is ignited by a spark plug. The explosion of the combustion pushes the piston down into the cylinder, producing the force that the transmission delivers to the drive wheels.
Common-Rail Injection
With the state-of-the-art common-rail direct fuel injection used in the S 320 CDI and S 400 CDI, Mercedes-Benz has achieved an ideal compromise between economy, torque, ride comfort and long life. Whereas conventional direct-injection diesel engines must repeatedly generate fuel pressure for each injection, in the CDI engines the pressure is built up independently of the injection sequence and remains permanently available in the fuel line.
The common rail upstream of the cylinders acts as an accumulator, distributing the fuel to the injectors at a constant pressure of up to 1600 bar. Here high-speed solenoid valves, regulated by the electronic engine management, separately control the injection timing and the amount of fuel injected for each cylinder as a function of the cylinder's actual need.
In other words, pressure generation and fuel injection are independent of each other. This is an important advantage of common-rail injection over conventional fuel injection systems.
Compact
A small car that can seat two to four people.
Compression Ratio
The ratio of the volume within an engine cylinder when the piston is at the bottom of its stroke, compared to the volume in the cylinder when the piston is at the top of its stroke. The higher the ratio, the more compression during combustion and the more powerful the engine.
Console
This may refer to the unit found between the front driver and passenger seat that contains the automatic transmission shifter, cupholders and a storage compartment. But it can also refer to the section of the instrument panel that includes the controls for the sound system and climate-control system, particularly if the panel flows down the center of the vehicle and includes the automatic-transmission shifter.
Constant-Velocity Joint (CV Joint)
On front-wheel drive and all-wheel drive vehicles, a coupling that allows the front axle to turn at a constant speed at various angles when the vehicle turns. The CV joint is a shaft that transmits engine power from the transmission to the wheel.
Continuously Variable Transmission
The most common type of CVT employs a steel belt and two pulleys. Rather than step among four or five gears of different sizes, the CVT varies the effective diameter of the drive pulley and driven pulley to create a broad range of drive ratios free of the shift feel of conventional transmissions.
Imagine riding a bike on which the sprocket and rear gear magically change size without requiring the chain to jump from one gear to another, and you have the basic idea. By increasing or decreasing the space between the pulleys' respective halves, the CVT varies the effective diameter of the conical inner surfaces on which the belt rides. It varies these parameters at any time, at any engine or vehicle speed. CVTs may use hydraulic pressure, centrifugal force and/or spring tension to adjust the pulley halves.
Smaller and more compact than a comparable automatic trans, the CVT is also somewhat more efficient, but its main advantage with regard to efficiency and fuel economy is that it can be designed to keep the engine running at its most efficient or powerful speed. By varying the drive ratio, a CVT can accelerate a vehicle when the engine rpm is constant or even decreasing.
Likewise, by limiting a gasoline engine's speed range, engineers can better control emissions. CVTs will become even more efficient as they incorporate automated versions of mechanical clutches akin to those in manual transmissions, in place of inefficient fluidic torque converters. Theoretically, CVTs can be more efficient than manual transmissions as well.
CVTs do have shortcomings, not the least of which is the fact that they're new technology compared to conventional automatics, though they are far more popular overseas. Belt-drive CVTs also are limited in the amount of torque they can handle, though refinements keep inching the capabilities upward. Audi is working on a CVT that uses a chain in place of a belt for a reported 200-plus pounds-feet of torque capacity. Even greater capacities are likely to come from designs using complicated roller arrangements in lieu of pulleys and belts, such as Mazda's Toroidal and Nissan's Extroid CVTs. These transmissions are not expected on these shores anytime soon, but Honda has offered a belt-drive CVT in the Civic HX since 1996 and will offer it on the Insight later in the 2001 model year. A new Saturn model will debut with a belt-drive CVT in 2002, and Audi's chain-drive CVT arrives in the 2002 A6.
Convertible
Any car with a removable top, either a rag (cloth) top or hard top.
Coolant
Liquid used to carry heat away from the engine. Sometimes called antifreeze.
Corporate Average Fuel Economy (CAFE)
The government tracks the average fuel economy of all the vehicles produced in a single model-year by each individual manufacturer. CAFE is that rating.
Coupe
Generally, a two-door car with close-coupled passenger compartment.
Craftsman Truck Series
These NASCAR Trucks are similar to a Winston Cup race car, under the skin. The body must be stock and its shape is monitored by NASCAR officials. This new series of races has been called one of the most exciting in motorsports.
Crankshaft
The shaft that converts the up-and-down motion of the pistons into rotation. It is connected to the transmission.
Crossmember
This component of a frame (or subframe), usually placed transversly, connects to and strengthens longitudinal frame rails.
Cruise Control
A device that, when set by the driver, will hold the car at the chosen speed.
Crumple Zone
Portions of a vehicle's structure designed to buckle and fold in an impact, absorbing crash force rather than transmitting it to vehicle occupants.
Curb Weight
The weight of the vehicle without passengers, driver or cargo, but with all standard features, a full tank of fuel, and all the fluids necessary for proper function.
Cylinder Block
The main part of the engine to which other parts are attached.
Cylinder Head
At the top of the engine block is the cylinder head which contains intake and exhaust valves. Air and fuel enter the cylinder head through the intake valves and spent leftovers are released after combustion through the exhaust valves.
Damper
A device that reduces vibration.
Daytime Running Lights (DRL)
These lights come on whenever the vehicle is turned on; they make the vehicle more visible to other drivers. Mandatory in Canada and standard equipment on many vehicles sold in the United States.
Depreciation
The decrease in a vehicle's market value over time. The amount of yearly depreciation is affected by vehicle condition; resale-marketplace supply and demand; and make and model reputation. Convertibles, high-performance cars, trucks and vans tend to depreciate less than other vehicles.
Diesel
An internal combustion engine in which the air-fuel mixture is ignited by compression in the cylinder rather than by a spark. Diesel engines use diesel fuel rather than gasoline and tend to be more fuel-efficient and require less maintenance than gasoline engines, but it is more complicated to get them to run cleanly. Also used as a slang term: after turning off the ignition, the engine continues to run for a short period.
Diesel Fuel
The fuel used by a diesel engine. Usually found in tractor trailers and other trucks.
Differential
A mechanical gearbox or fluid coupling that allows wheels to rotate at different speeds. Usually located on an axle, it allows the outside wheels to turn faster than the inside wheels during cornering. Four-wheel-drive and all-wheel drive vehicles have two differentials, one for the rear axle and one for the front. all-wheel drive vehicles also may have a third or center differential on the drive shaft that runs between the front and rear axles.
Differential Lock
The main disadvantage of an "open" differential is that the usable torque is restricted by the wheel with the least traction. A differential lock literally locks out the differential action and forces torque to be split equally between each wheel (or each axle)for maximum traction. In a rear-wheel drive vehcile, for instance, locking the rear differential locks the left and right rear wheels together so that both receive equal torque.
In a full-time or permanent four-wheel drive wehcile, locking the center differential locks the front and rear drive-shafts together, sending equal torque to the front and rear axles. While locking a differential helps increase traction, it makes steering more difficult on high-traction surfaces because it tends to force the vehcile to travel in a straight line.
Ding
A small dent or scrape in the body of the vehicle.
Disc Brakes
Shiny metal discs, called brake rotors, are attached to the wheel hub, rotating with the wheel. When the brake pedal is depressed, the brake calipers squeeze the discs to slow the vehicle. See Brake Caliper and Brake Rotor.
Displacement
The volume displaced by an engine's cylinders. Formerly measured in cubic inches, it is now more commonly expressed in liters.
Distributor
Part of the ignition (electrical) system. Delivers electricity from the ignition coil to the distributor cap and the spark plug wires in the correct firing order. (The firing order is that sequence in which each cylinder begins its power stroke.) The spark plugs ignite the fuel and air mixture in each cylinder thousands of times a minute, producing the explosion that pushes the piston down in the cylinder to power the vehicle.
Distronic
Distronic is derived from the words "distance" and "electronic". It operates much like a conventional cruise control system. However, when in cruise mode, with Distronic, the system senseds the approach to a slower vehicle and automatically slows the car down to maintain a set following distance.
If the other vehicle speeds up or you switch lanes, the system resumes the original speed setting. The system will apply up to twenty percen of maximum braking force. If more braking is needed, an audible beep and a red warning triangle light on the dash, comes on to alert the driver.
Double Wishbone Suspension
A type of independent suspension in which the upper and lower support pieces, or members, look somewhat like a wishbone.
Drafting
A phenomena where two cars running nose to tail together can move faster than an individual vehicle.
Drive Axle
Connects the transaxle to the front wheels on a front-wheel drive vehicle.
Drive Range (EV)
The distance an electric vehicle can drive without re-charging its batteries.
Drive Shaft
A rotating metal shaft that transfers power from the transmission differential gear assembly to the rear wheels on a rear-wheel drive vehicle.
Drivetrain
Vehicle components which act together to move the vehicle forward or backward. On a rear-drive vehicle, it is the combination of the engine, transmission, differential and drive shaft. On a front-drive vehicle, it consists of the engine, transaxle and drive axles.
Drum Brakes
A braking system that uses a metal drum. Brake shoes press against the drum to slow or stop the car.
Dual Overhead Cam (DOHC)
Engine with two camshafts on top of the cylinder head, one to open and close intake valves, the other to open and close exhaust valves. See also Overhead Cam and Overhead Valve.
Electric Vehicles (EV)
Vehicles powered by electricity, generally using a rechargeable battery.
Electronic Brake Force Distribution
This system controls the balance between front and rear brake forces to optimize braking efficiency across all vehicle loading and driving conditions. The system also promotes increased brake pad life.
Electronic Control Module (ECM)
The computer that controls the engine's fuel and emissions systems. Among the devices it controls is the idle air control, or IAC, which regulates the idle speed in fuel-injected engines. Also called the Electronic Control Unit (ECU).
Electronic Fuel Injection System
Injects fuel into the engine's cylinders with electronic control to time and meter the fuel flow.
Electronic Stability Program
ESP monitors the vehicle's response to the driver's steering and braking inputs to detect oversteer or understeer. If sensors detect that a skidding condition is developing, ESP brakes individual front or rear wheels and/or reduces excess power as needed to help keep the vehicle going in the direction the driver is steering.
What does the ESP off switch do?
The switch disables ESP's capability to reduce the engine torque. It also reduces the ESP intervention threshold to about 20%.
How do I know ESP is working?
The triangle in the center of the speedometer flashes when ESP intervenes; either with ESP switched on or off. It's a reminder to adjust your speed to the prevailing road conditions, usually by reducing it. If instead one "steps on it", with ESP ON, the engine power may be reduced to prevent a potentially critical situation. Electronic Stability Program (ESP®)
The standard-fitted ESPĀ® system selectively applies braking forces to the front and rear wheels in such a way as to reduce the risk of skids and slides and help the driver maintain control in critical situations. The system extends the technology of the anti-lock braking and acceleration skid control systems with a range of additional sensors which are used principally to detect yaw motion. The ESPĀ® computer continuously compares the actual behaviour of the vehicle with the computed ideal values. The moment the car deviates from the direction intended by the driver, specially developed control logic causes the system to intervene with split-second speed to bring the car back on track. It does this in two ways:
- Precisely controlled braking at one or more wheels
- Reducing engine power.
ESP® in this way helps to stabilise the vehicle in critical situations.
Electronic Valve Timing (EVT)
System in which a computer controls the timing of the opening and closing of cylinder valves.
Engine Braking
This term describes the driving technique of slowing a vehicle by taking your foot off the throttle, particularly in a lower gear (such as first gear/Low Range). Engine braking uses the compression of the engine and the low gearing of the transmission/transfer gearbox to slow the vehicle.
Engine Displacement
The total of the volume used for combustion inside the cylinders of an engine. Measured in liters on newer models, or in cubic inches on older models.
Environmental Protection Agency (EPA)
The federal agency that regulates air quality and sets automotive fuel-economy and emissions standards.
Evaporative Emissions
Evaporated fuel from the carburetor or fuel system which mixes with the surrounding outside air.
Evaporator Core
Part of the climate-control system that contains a liquid refrigerant which turns to gas to absorb heat from the air.
Excess Wear and Tear
Visible damage to a vehicle that is above and beyond what is considered normal wear and tear. Usually specified in the lease contract. Will incur additional cost at lease-end. If possible, negotiate as specifically as you can in the lease what the lessor will consider excess wear and tear.
Exhaust Gas Recirculation (EGR)
Part of the emissions system, it recirculates exhaust gases into the intake manifold, cooling the combustion chamber.
Exhaust Manifold
The passages that route the exhaust gases towards the muffler and exhaust system.
FIA
Federation Internationale De L'Automobile
Factory Equipment
The standard and options that make up the equipment of a used vehicle.
Fan Belt
Transmits power from a crankshaft-driven pulley to an engine fan and other accessories.
Fifth Wheel
Provides a flexible connection between the tractor and the trailer.
Final Drive Ratio
The reduction ratio of the transmission gear set furthest from the engine. In other words, the ratio of the number of rotations of the drive shaft for one rotation of a wheel. In general, a low final drive ratio results in better fuel efficiency, and higher final drive ratio results in better performance.
Firewall
The metal panel that separates the engine compartment from the passenger compartment. It also often includes sound and heat insulation.
Formula 1
The most popular of all the forms of auto racing, Formula 1 tends to be dominated by European drivers. The parallels to Indy Car racing have lead to the defections of drivers like Nigel Mansell, who seek the greater spoils of victory here in the US.
Four-Wheel Steering
Vehicle on which all four wheels turn when the driver turns the steering wheel. The rear wheels turn at a smaller angle than the front wheels. This system appeared on a few sports models in the 1980s but was never very popular in North America.
Front-Wheel Drive
Engine power is transmitted to the front wheels, which are the drive wheels. Also front-drive.
Fuel Economy
The number of miles a vehicle gets per gallon.
Fuel Injector
Taking the place of carburetors in the 1980s, the fuel injector is an electrically controlled valve that delivers a precise amount of pressurized fuel into each combustion chamber.
Fuel Injection
A mechanical system to inject atomized fuel directly into the cylinders of an internal-combustion engine; avoids the need for a carburetor.
Fuel Pump
A mechanical or electrical pump that pressurizes the fuel system to move gas from the fuel tank to the engine.
Full-Size
A car that is usually four doors and seats anywhere from two to seven people.
Fuse
An electrical device that breaks the current in a circuit that is overloaded or shorted; it prevents damage to other components. However, the fuse itself may fail, and the most common repair when a fuse blows is to simply replace it without working on any other electrical component.
Gas-Charged Shocks
Also called gas-filled shocks. They are shock absorbers filled with a low-pressure gas to smooth the vehicle's ride during up-and-down movement.
Gasket
Any thin, soft material installed between two metal surfaces to create a good seal.
Gasoline Alley
This is the garage area at Indy, where major mechanical work is done on the cars.
Gasoline Alley
This was the previous name for Winston Cup Racing before R.J. Reynolds became the sponsor in 1972.
Grand Prix
A type of car race popular in Europe. Also, a French term meaning great prize.
Greenhouse
Used in automotive circles to describe all of the windows enclosing the passenger compartment.
Grille
An opening in the front of the vehicle that allows air to reach the radiator.
Gear Ratio
This is a numerical ratio of a series of gears in relation to each other, based on the number of turns of the input shaft, compared to turns of the output shaft. Gear ratios are determined by the number of teeth on each gear (and therefore the size of each gear). For instance, a gear with 36 teeth meshed with a gear with 12 teeth gives a 36/12 or 3/1 ratio. This is usually expressed as 3.00:1.
Gross Axle Weight Rating
The maximum amount of weight that can be supported by each axle, as designed by the manufacturer.
Gross Combined Weight Rating
Gross Combined Weight Rating = vehicle GVWR = trailer GVWR. It is the maximum allowable weight of a completely loaded vehicle and trailer, as designated by the manufacturer.
Gross Vehicle Weight
The total weight of a vehicle with driver and passengers, cargo fuel, coolant, any options or accessories, and tongue weight if towing.
Gross Vehicle Weight Rating
The maximum allowable total weight of the vehicle that may not be exceeded, as designated by the manufacturer. GVWR is identified on the manufacturer's certification label, which is usually located on the driver's door or door jam. GVWR is the combination of curb weight plus payload (including driver and fuel).
Ground Clearance
With the vehicle stationary, ground clearance is the measurement from the lowest-hanging point under the vehicle (usually a differential or the exhaust system) to the ground. A high ground clearance allows a vehicle to drive more easily off-road or through heavy snow without damaging underbody components. Ground clearance can also be measured at other key oints, such as under the frame, in order to help drivers navigate off-road obstacles.
Hatchback
A passenger car with a full-height rear door that includes a rear window. Usually has a rear folding seat.
Hazard
A situation that may increase the probability of a loss or damage.
Headliner
The interior covering of the roof. Headliners often contain consoles with slots for garage-door openers and other devices, as well as dome lights and wiring for electrical and electronic components attached to the headliner. The covering usually includes a sound-absorbing material.
Horsepower (hp, bhp)
Abbreviated as hp, as in 200-hp engine, or bhp (brake horsepower or net horsepower) to designate power produced by an engine. In general, the higher the horsepower, the higher the vehicle's top speed. One horsepower is the power needed to lift a 550-pound weight one foot in one second.
Hot Rods
With the vehicle stationary, ground clearance is the measurement from the lowest-hanging point under the vehicle (usually a differential or the exhaust system) to the ground. A high ground clearance allows a vehicle to drive more easily off-road or through heavy snow without damaging underbody components. Ground clearance can also be measured at other key oints, such as under the frame, in order to help drivers navigate off-road obstacles.
Half-Shaft
A half-shaft is an articulating, rotating shaft used in independent suspension systems to transmit power from a differential to a wheel. The term is also used to describe a non-articulating axle shaft.
Hauling/Payload Capacity
The maximum amount of weight, including driver, passengers, options or accessories, that can be carried in the truck's bed and cabin, and tongue weight if towing. Exceeding a vehicle's payload capacity can negatively affect steering and damage the suspension.
I-Beam Suspension
A suspension beam under the car that supports the body in the shape of a capital I.
IHRA
International Hot Rod Association
IMS
Indianapolis Motor Speedway, the site of the Indy 500. This is now an IRL event.
IMSA
International Motor Sports Association, founded by John Bishop in 1969. Sanctions, organizes, markets and officiates professional auto racing events. Season begins in February at Daytona International Speedway and ends in October on the streets of New Orleans.
IRL
Indy Racing League founded by Tony George in 1995 in response to re-occurring feuds and disputes with CART.
IROC
International Race of Champions
Idle Speed
The speed of the engine at minimum throttle and the engine in neutral.
In-Line Engine
Cylinders are arranged side by side in a row and in a single bank. Most four-cylinder and some six-cylinder engines are in-line engines. In V-6, V-8 or V-12 engines, the cylinders are divided into two banks, each of which is angled away from the other in a 'V'.
Independent Suspension
A suspension design that lets each wheel move up and down independently of the others. A vehicle can have two-wheel or four-wheel independent suspension; sportier models have four-wheel independent suspension. See also Multi-Link Suspension, Live Axle.
Indy 500
The big race held in Indianapolis every year on Memorial Day weekend.
Indy Lights
One level below Indy car racing, known for its lighter version of actual Indy Cars. This is a stepping stone to the Indy 500.
Inflatable Tubular Restraint
This tube of woven material is stiffer and stays inflated longer than a traditional airbag cushion. The tube protects the occupant's head and torso in a side impact, in part by keeping them away from the point of intrusion. The uninflated tube is tucked into the edge of the roof headliner. The tube is attached at the base of the A-pillar in front of the occupant, and at the roofline behind the occupant. When it inflates, the tube angles across the window to keep the occupants head from hitting the window glass or metal side pillar. Because of the longer time the tubular restraint stays inflated, it is expected to also offer protection in a rollover.
Instrument Panel
The instrument panel contains the gauges in front of the driver; the controls for the sound system and climate-control system; the glove box; vents for the windshield defroster; and the front passenger-side airbag. The instrument panel is often delivered to the factory as a complete module with electronic components already installed.
Integrated Child Seats
May also be called integrated child-safety seats or integrated child-restraint seats. Built-in child seats that fold out of the seatback of a rear seat. Sedans with this option usually have one in the center of the rear seat; minivans may have one or two in the middle seating positions. While NHTSA and every other safety organization stress that any child-restraint seat is better than none, built-in child-restraint seats are considered the safest alternative because they are more securely anchored than a seat attached to seat belts.
Intercooler
Device that cools air as it leaves a turbocharger or supercharger before the air is blown into the engine air intake. Cooling makes the air denser and richer in oxygen, which lets the engine produce more power.
Interior Payload
The amount of space or material that can be carried inside the vehicle.
Jalopy
(Slang) An old, dilapidated automobile.
Joint Tenancy
Ownership that is shared by two or more persons.
Jounce
Jounce is the motion of a wheel that compresses its suspension. Full jounce refers to a wheel that is at the upper limits of its travel. A jounce bumper or jounce stop is an elastic "cushion" used to stiffen the suspension gradually as it approaches the end of its jounce travel. Jounce is the opposite of rebound.
Keyless Entry
A system for locking and unlocking doors of a vehicle with a central locking system without using the key. Usually, the user controls the locks by pressing a button on a remote key-fob transmitter. Some vehicles have electronic combination locks on the doors near the handle.
Kilometers Per Hour (KPH)
Multiply by 0.621 to convert to miles per hour.
Kit Car
A vehicle that is designed for assembly by the private hobbyist.
Ladder Frame
A ladder frame, shaped like a large ladder, is used in body-on-frame construction. Two long "rails" run along the sides, with crossmembers connecting the two. This type of frame is used in most pickup trucks and sport utility vehicles. However, differences exist in shape, structure and thickness of the various elements.
Lap-and-Shoulder Belt
A safety belt that secures the driver and/or passenger in the seat with a continuous web of material which fits across the lap and crosses the upper body. It keeps the occupant from jerking forward in the event of a crash. Also called three-way belt, three-point belt, or three-point safety harness.
Lapse
The termination of a policy due to failure to pay the premium.
Leaf Spring
Suspension spring made up of several thin, curved, hardened-steel or composite-material plates attached at the ends to the vehicle underbody. The curved shape of the plates allows them to flex and absorb bumps.
Lean or Rich Fuel Mixture
The fuel mixture is lean when it has too much air, and rich when it has too much fuel. These terms can also be used to refer to adjustments the electronic control module makes to the fuel mixture in response to various driving conditions, particularly on engines with variable-valve technology.
Leg Room
With the front seat adjusted all the way back, the distance from the accelerator pedal's heel point to the back of the front seat cushion.
Lemon
(Slang) A vehicle, usually new, that has a large number of defects.
Lift Gate
The rear opening on a hatchback.
Light-Duty
Adjective that refers to passenger trucks, as opposed to medium-duty or heavy-duty commercial trucks.
Limited-Slip Differential
A device that helps prevent the drive wheels from skidding or losing traction by diverting power from the slipping wheel to the opposite wheel on the same axle.
Linguatronic
The innovative voice control system LINGUATRONIC (optional), which Mercedes-Benz was the first car manufacturer in the world to develop for operating the car telephone, can also be used to control the navigation and audio systems of the S-Class. The system receives the driver's wishes by microphone and then starts up a short interactive dialog. For instance, a pleasant female voice answers the command "dial number" with the request "the number, please", and after the driver has spoken the phone number and said "dial", the system automatically starts dialling. In response to the command "CD player" or "CD changer", music very soon starts to flow from the loudspeakers.
The heart of the LINGUATRONIC system is a software package which is programmed with voice recognition algorithms and which can take into account the individual peculiarities of the human voice. Consequently, the system can adjust to the individual speaking style of the different users and can thus also understand dialects.
Liter
Engine-displacement measurement, as in 2.0-liter engine.
Live Axle
A live axle is a solid axle that transmits power to a pair of wheels. It is composed of a rigid axle with a differential and axle shafts to power two wheels. It is called "live" because it has engine power flowing through it. A solid axle that does not transmit power is called a beam axle.
M+S Rating
A tire rating which indicates a tire designed to perform well in mud and snow.
MIS
Michigan International Speedway. Site of the 1996 US 500, a CART event.
MacPherson Strut
A MacPherson strut is a unit that includes a damper or shock absorber cartridge inside a large, long metal spring. MacPherson struts are used over the front wheels of most front-drive cars. Replacement of MacPherson strut cartridges requires a spring compressor.
Make
The manufacturer of the vehicle (BMW, Chrysler, Honda).
Manifold Absolute Pressure Sensor (MAP sensor)
Detects engine load by measuring air pressure or vacuum in the intake manifold.
Manual Stick Shift
Select Shift Manual (SSM) and Auto Shift Manual (ASM) use a combination of Auto-Clutch and Shift-By-Wire electronic control system technology to provide the customer a fun-to-shift experience along with significant fuel economy improvements over a base manual transmission. The Select Shift Manual mode allows a customer to command gear changes according to his/her personal preference like a conventional manual transmission. The Auto Shift Manual mode provides the customer automatic gear shifting much like an automatic transmission.
Both the Auto-Clutch subsystem and Shift-By-Wire subsystem use an electro-hydraulic or electro-mechanical actuation system controlled by a stand-alone transmission control module. A customer requests a gear shift by using the appropriate driver interface mechanism (shift lever, push buttons, etc.)
In place of the usual cable/linkage (which is eliminated), a sensor informs the controller of the requested gear shift. The controller processes the request and commands the actuators to open/close the clutch and disengage/engage the gear sequence with very fast response times. Engine torque is controlled during the shift either by controlling the throttle directly (Drive-By-Wire) or enabling ignition/fuel injection control to provide smooth shifts.
Mass Airflow Sensor
Device that measures the flow of air entering the throttle housing.
Master Cylinder
A piston-type pump that produces pressure in the brake hydraulic system.
Mid-Size
A medium size car designed to seat four to six passengers.
Minimum Ground Clearance
The distance between the ground and the lowest point of the vehicle chassis (usually the axle). A vehicle can drive over any object shorter than its minimum ground clearance.
Model
The style of the vehicle produced by the manufacturer (Ford Mustang, Chrysler LeBaron, Honda Civic).
Moonroof
A window-type opening in the roof of the car that can open or tilt up or down. See Sunroof.
Muffler
The exhaust system device in the tailpipe that reduces engine noise. Some vehicles have more than one muffler along the tailpipe.
Multi-Link Independent Rear Suspension
Multi-link independent rear suspension was developed on the basis of research into optimised wheel movement geometry, conducted with the aid of practical testing and computer simulations. A wheel not constrained by attachment to an axle has six possible degrees of freedom: it can move in vertical, horizontal or perpendicular direction and it can also rotate about these three directions.
The suspension engineers seek to prevent such uncontrolled kinematic behaviour and to restrict the freedom of the wheel to move on anything but a carefully pre-scribed path. They therefore attached the wheel to five separate, flexibly mounted links, which limit it in five of its degrees of freedom. This ingenious arrangement of links leaves each rear wheel just one degree of freedom - controlled compression and rebound.
Multi-Port Fuel Injection
An electronic fuel-injection method that uses individual injectors to spray fuel directly into each intake port, bypassing the intake manifold. Also called multi-point fuel injection.
Multi-Plate Transfer
A component that can act as a differential or a slip-limiting device, a multi-plate transfer (or multi-plate clutch) is a set of several hydraulic clutches that are progressively engaged and disengaged to limit slip and/or allow differential action of the wheels. Most MPTs are computer-controlled, with speed sensors to determine when to engage/disengage the clutches. Some Ford Explorers and Chevrolet Tahoes, for example, use an MPT in place of a center differential.
NASCAR
National Association of Stock Car Auto Racing; the governing body which sets the rules and regulations for stock car racing.
NHRA
National Hot Rod Association
National Highway Traffic Safety Administration (NHTSA)
The federal agency that creates safety regulations for cars and trucks, crash-tests them, and analyzes safety-related defects that may require recalls.
Nitromethane
A mixture of nitric acid and methane which is used to fuel TOP Fuel Dragsters and Funny Cars; is also called nitro or top fuel.
OCIR
Orange County International Raceway.
Octane
The hydrocarbon substance in gasoline that reduces engine knock or pinging, which is a noise caused by premature ignition of fuel in the cylinder combustion chamber. The higher the octane number, the less chance of premature ignition. High octane, which has a rating above 91, is useful only when recommended by the manufacturer.
Odometer
Indicates the number of miles a vehicle has been driven. It is illegal to tamper with the odometer reading.
Overdrive
A transmission gear with a ratio below 1:1, which improves fuel economy by reducing engine revolutions per minute at highway speeds. On a five-speed manual transmission, the fourth and fifth gears are overdrive. On a four-speed automatic transmission, the fourth gear is overdrive. When an overdrive gear set is engaged, the output shaft turns at a higher rate than the input shaft, reducing engine revolutions at cruising or highway speeds.
Overhead Cam (OHC)
The camshaft is on top of the cylinder head on overhead-cam engines. Single overhead-cam (SOHC) engines have a single cam above the cylinder head. Dual overhead-cam (DOHC) engines have two cams above the cylinder head. All overhead-cam engines are also overhead-valve (OHV) engines, which means the intake and exhaust valves sit atop the cylinder head.
Oversteer
Occurs when the rear tires lose adhesion under cornering. In motorsports, this is also called loose. Oversteer can lead to a spin if the driver doesn't reduce acceleration. See also Understeer.
Oxygen Sensor
Measures the amount of oxygen in the exhaust.
On-Demand
While this was originally a name marketed by Subaru for its part-time Four-Wheel drive system, it is now used to describe the action of some full-time Four-Wheel drive systems. Typically, torque is sent to the rear wheels until the front wheels "demand" more because the rear wheels are spinning. At that point, torque is distributed more equally.
PPG
Actually, PPG Industries, founded in 1883 as the Pittsburgh Plate Glass Company. PPG has been the source of tough urethane finishes on cars racing in the Indianapolis 500 since 1975. In 1980, it became the title sponsor of the PPG Indy Car World Series.
PRO
Professional Racers Organization
PSI
Acronym for pounds per square inch. A pressure measurement used in tire inflation and turbocharger boost.
Pace Car
Seen at NASCAR and Indy races, the pace car leads race cars out of the pole position at beginning of races or after a yellow flag or restart has been called.
Package Shelf
The ledge between the rear seat and the backlight (or rear windshield). The name is misleading because it's a bad idea to put anything on the package shelf. However, it often contains the sound system's rear speakers and, on some vehicles, the CHMSL or center brake light. Sometimes also called the package tray. On European cars the package tray often contains a first-aid kit; on higher-end models it may contain storage compartments.
Papers of Origin
Manufacturer documents used to obtain vehicle titles.
Passive Restraint
A device or structure that automatically helps restrain vehicle occupants in an impact. This includes airbags, belt pretensioners, padded knee bolsters, and shoulder belts that are motorized, or attached to the door.
Pick-up
The type of truck with an open cargo bed behind the closed cab.
Pinion
A type of gear that has small teeth that mesh with other, larger gears.
Piston
The heavy, cylindrical metal shaft within each engine cylinder that travels up and down to turn the crankshaft, compress the air and fuel mixture for combustion and expel exhaust gases.
Positive Crankcase Ventilation Valve
An emission device that routes oil pan vapors to the intake manifold to be burned during combustion. Also known as the PCV valve.
Power Plant
Another name for a vehicle's engine.
Power Steering
A steering system that uses a separate motor or engine power to reduce the effort necessary to turn the front wheels.
Power-to-Weight Ratio
The maximum power output of the vehicle per unit mass. The higher the ratio, the more powerful the vehicle. In comparing several vehicles, this can be a better measurement than engine horsepower or torque because it considers the weight variable. In other words, a car that seems to have a powerful engine but is also heavy may have less get-up-and-go than a vehicle that has a similar or less powerful engine but also weighs less.
Powertrain
The combination of engine and transmission.
Pressure Plate
Holds the clutch disc against the flywheel.
Pretensioner
A device that rapidly yanks in shoulder-belt slack when a crash sensor detects an impact. Some pretensioners are activated by a small explosive charge in the belt retractor; some contain their own inertial sensors. So far, pretensioners are still found on more expensive models, particularly those by European manufacturers. By pulling in belt slack within milliseconds of an impact, pretensioners help reduce chest and head injury by restricting occupant motion and preventing the occupant from hitting the belt.
Pro Rallies
Road rallies which are very competitive and are run at high speeds on roads closed to the public. Often sponsored by the SCCA.
Pro Start
A method of starting a drag race that differs from most starts in that it only has one amber light between the initial staging and the final lights on the "Christmas Tree".
Projector-Beam Headlights
A headlight that uses a spherical reflector to tightly control the light beam. The bulb or light source directs the light inward, toward the reflector at the back of the headlight assembly, which then projects it forward from the vehicle. These lights are more powerful, accurate and expensive than standard sealed-beam and halogen headlights, and are generally found on sport and luxury models.
Pushrod
A metal rod that transmits the motion of the camshaft to the valve actuators to open and close the valves. Used on engines with overhead valves but without overhead camshafts.
Quarter Panel
Sheet of metal panel that covers the front and rear quarters of the vehicle.
R-12
The chlorofluorocarbon refrigerant, commonly referred to as Freon (a DuPont trademark) or CFC-12, now considered environmentally hazardous but once the key ingredient in automotive air-conditioning systems. A refrigerant is a chemical compound that absorbs, carries and releases heat in an air-conditioning system.
R-134a
The environmentally safe refrigerant now used in air-conditioning systems. It requires a slightly bulkier condenser unit than R-12. Vehicles equipped with R-12 systems can be converted to use R-134a. Since Freon is now banned, expensive and hard to obtain, the conversion may be a good idea when an R-12-based system needs recharging, particularly if technicians detect a leak.
RACMSA
The RAC Motor Sports Association is recognized by the FIA as the governing body of motor sport in Great Britain.
Rack and Pinion Steering
The steering wheel is connected to a pinion gear that meshes with a toothed bar, also called a rack or linear gear. As the pinion turns, the rack moves side to side, moving the steering linkage and causing the front wheels to turn left or right. The ends of the rack are linked to the steering wheel with tie rods.
Radiator
The copper or aluminum device in front of the engine through which hot engine coolant is circulated and cooled. The liquid is then recirculated back through the engine block to cool it.
Rag Top
A convertible with a soft top.
Rally
Competing teams, consisting of a driver and a navigator, are given route instructions, which they must follow exactly. Each team follows the course independently, trying to rack up points based on how well they meet a pre-determined schedule.
Ramp Breakover Angle
This is a measure of a vehicle's ability to drive over a sharp ridge or ramp without touching its underside. The "included" angle measures the angle inside the ramp; the "exluded" angle measures the combined angles outside the ramp to the horizontal. A short-wheelbase vehicle with a high ground clearance and large tires will have the best (highest) ramp breakover angle.
Rebound
Rebound is the vertical motion of a wheel that extends the suspension. When a wheel is in full rebound, it is fully extended to the limits of its travel. Rebound is the opposite of jounce.
Recall
A manufacturer calls in vehicles to repair defects, usually safety-related. Recalls may be voluntary, requested by the government, or mandated by NHTSA.
Recirculating Ball
A steering mechanism in which the steering shaft turns a worm gear causing a toothed metal block to move back and forth, turning the front wheels. Ball bearings reduce friction between the worm gear and the metal block.
Recovery Strap
A recovery strap is a strap made of elastic nylon with "eyes" on both ends. Unlike a simple rope or chain, a recovery strap uses kinetic energy (like a rubber band) to help free a stuck vehicle using another vehicle.
Redline
The point on the engine tachometer that indicates the maximum rpm the engine can safely withstand.
Release Fork
Disengages the clutch disc from the flywheel by pressing on the pressure plate release springs.
Revolutions Per Minute (RPM)
Describes at which speed the engine crankshaft is turning.
Rims
The outer edge of a bare wheel.
Rocker Panel
The body panel that runs beneath a vehicle's doors.
Rollcage
A protective steel cage to prevent driver injury during a rollover.
Rollover
The type of vehicle impact in which the car or truck rolls over on its side, onto its roof, or turns over completely. The biggest cause of injury in a rollover is ejection of the occupant or any part of the occupant. Rollover is a greater risk in any sport-utility vehicle -- because of its high center of gravity -- than in a minivan, pickup truck or passenger car. Rollover can occur immediately upon impact or in the seconds after an impact, which makes it more difficult to protect occupants with traditional airbags. Inflatable tubular restraints and similar designs that stay inflated longer than traditional airbags will be more effective in rollover situations.
SCCA
The Sports Car Club of America sponsors many racing events in the U.S. It also supplies many of the Race Officials and Workers for Road Racing by other groups. Most SCCA events are geared toward participation by SCCA members.
SCORE Off-Road Desert Championship
Short Course Off-Road Enterprises. SCORE now stages and promotes Off Road Truck races and events. Season starts in Arizona each January, ending in November with the Ford Tecate SCORE Baja 1000.
SRP
Spokane Raceway Park
Sedan
A two- or four-door car that can hold four to six people. Includes a trunk in the rear.
Sensor Algorithm
An algorithm is a mathematical formula or series of formulas used by an on-board computer or processor to make a decision. In an airbag system, a crash-sensor algorithm determines whether the change in velocity indicates an impact of great enough force to require airbag deployment, based on pre-programmed parameters. If the change in velocity is great enough, the processor sends a signal to the device that inflates the airbag.
Sequential Fuel Injection
A sequential fuel injection system times the opening of the injectors to match the opening of the intake valve into each cylinder.
Shift Interlock
On a vehicle with automatic transmission, a safety device that prevents the driver from shifting out of park unless the brake pedal is depressed.
Shift-On-The-Fly
Older-style part-time Four-Wheel drive systems sometimes required drivers to stop and lock the front hubs before engaging four-wheel drive. Most SUVs now have automatic locking front hubs and the ability to shift "on-the-fly" (at speed) from two-wheel drive to four-wheel drive. However, many limit the speed at which this can be done (usually less than 50 mph and sometimes as low as 15 mph), and many still require the driver to stop and back up to fully disengage Four-Wheel drive.
Shock Absorbers
Suspension device near each wheel that dampens the up-and-down movement of the vehicle. Inside a shock absorber, a piston rides up and down in a cylinder filled with thick fluid or compressed gas. The shock absorber counteracts the up-and-down movement allowed by the springs.
Side Airbag
An inflatable cushion that fills the space between the door and the occupant to prevent head, torso and pelvis injuries when a vehicle is hit from the side. Side airbags may be stored in the door-trim panel or the outboard side of the seat; they may protect the hip and torso only or also protect the head. A new design, called an inflatable tubular restraint, is stored in the edge of the roof headliner and attached at the base of the A-pillar at the front end and above the doors along the roofline at the other. The device inflates into a somewhat stiff tube that prevents the occupant's head from hitting the side pillar or the window.
Side-Impact
Federal safety regulations require that vehicles absorb a certain amount of force when hit from the side. To meet side-impact standards, automakers have stiffened side-impact beams, which resist intrusion into the passenger compartment, and added safety devices such as side airbags and extra padding, which are designed to push the occupant toward the interior of the vehicle and away from the point of intrusion.
Single Overhead Cam (SOHC)
An engine with a single overhead cam generally has one intake and one exhaust valve per cylinder; the single cam opens and closes both valves. See also Overhead Cam and Dual Overhead Cam.
Skidplate
This term refers to a protective cover or "plate" under a vehicle that covers vulnerable components, such as the transmission/transfer gearbox, engine oil pan or fuel tank.
Slicks
A type racing tire characteristically very wide with no tread.
Smart Airbag
Smart airbags don't exist yet, but NHTSA expects automakers and their suppliers to have them perfected sometime after the year 2000. There are many designs, but each contains similar elements including a system of sensors and mathematical algorithms to detect the presence or absence of an occupant in the seat; to determine the size, weight and nature of any occupant (including whether it is a rear-facing infant and determine whether the occupant is an adult, a dog, a bag of groceries or a rear-facing infant seat); and to determine whether the occupant is too close to the airbag door for safe deployment. A smart system will use that information to decide whether to inflate the airbag in an impact. Later generations of smart airbags will adjust the rate of inflation based on force of impact and size of the occupant.
Society of Automotive Engineers (SAE)
An engineering organization that shares research information and sets industrywide standards.
Solo I
A racing event sponsored by the SCCA, focused on Time Trial and Hill Climbs.
Solo II
Autocross racing event sponsored by the SCCA.
Spark Plug
Converts voltage into an arc that passes between its electrodes; the arc ignites the fuel-air mixture in the combustion chamber. The mixture explodes, creating power by pushing down the piston.
Spoiler
Usually on the rear of the vehicle, it changes the direction of airflow in order to reduce drag.
Sport Utility Vehicle (SUV)
Refers to a style of truck which has a square passenger cabin and hatchback, and may be equipped with two- or four-wheel drive.
Sports Car
A body type designation. Generally a small, powerful car seating only two people.
Sprint Car
Two types of sprint cars exist, the first is the USAC open-wheel cars that feature a upright roll cage. The second is a similar car that has a large wing mounted to the top for stability; this is used by the World of Outlaws.
Starter
An electric motor powered by the battery that turns the crankshaft before the pistons begin operating.
Starting Grid
The first section or portion of a race track.
Station Wagon
A two- or four-door passenger car with a cargo area that extends all the way to the rear bumper.
Steering Ratio
The ratio of the different steering gears. Usually a lower gear means a faster response.
Stock Car Racing
Started by NASCAR's founder, Bill France, in the 1940s. Initially meant track cars equipped with showroom parts. Today, few cars use stock parts. Most are built from custom parts, made especially for these race cars, that look like those in showrooms.
Stroke
The up-and-down distance the piston travels within the cylinder. On a traditional internal combustion engine, the piston makes four strokes during the combustion cycle, only one of which is a power stroke. On the power stroke, the piston is near the top of the cylinder, and it has compressed the air and fuel mixture. The spark plug ignites the mixture, and the force of the explosion pushes the piston down into the cylinder, producing the force that turns the crankshaft. The piston returns to the top of the cylinder to expel the exhaust gases on the second, or exhaust, stroke. It slides down to the bottom of the cylinder during the intake stroke, when the valves open to let in air and fuel. The piston rises to the top of the cylinder on the compression stroke to begin the cycle anew. This process repeats hundreds or thousands of times a minute, resulting in the number of crankshaft revolutions per minute at which the crankshaft is rotating.
Strut
A strut is a suspension element in which a reinforced shock absorber is used as one of the wheel's locating members, typically by bolting the wheel hub to the bottom end of the strut.
Subcompact
The car size class one step up from the minicar.
Subframe
A subframe is a small, separate frame usually attached to a unitized-body vehicle. A front subframe might be used to "cradle" the engine and transmission, while a rear subframe would attach the rear suspension to the unibody structure.
Sunday Afternoon Rally
One day rallies, usually run by a local car club. These may be run on public access roads.
Sunroof
A window-type opening in the roof of the vehicle that can tilt or slide open.
Supercharged
Serves the same function as a turbocharger but avoids lag time because it runs off an engine-driven pump. Both turbochargers and superchargers are used to produce more power without increasing engine displacement, but neither are particularly fuel efficient and both can require costly maintenance as vehicles age.
Suspension
Springs, shock absorbers, struts, and links used to suspend the frame, body and engine above the wheels.
Suspension Travel
This term refers to the amount of vertical wheel movement allowed by the suspension, from full jounce to full rebound.
Swaybar
Also called an anti-roll bar or stabilizer bar, this suspension element is a long torsion bar (essentially a rod that can twist)mounted across the vehicle from one wheel to the wheel on the opposite side. By transferring movement and force from one side of the vehicle to the other, a sway bar can restrict body lean (or sway) during cornering. Vehicles may have sway bars in the front, rear or both locations.
Synthetic Oil
Engine lubricant not derived from raw petroleum. It has superior engine-protection properties but costs as much as five times more than petroleum oil.
Tachometer
The instrument gauge that shows engine speed, or revolutions per minute. On a vehicle with manual transmission, the driver can use the tachometer to tell when to upshift or downshift. Also called tach.
Tappet
A pivoting actuator that opens and closes cylinder intake and exhaust valves.
Teleaid
The optionally available TELEAID automatic emergency call system is based on the built-in telephone. Following an accident it automatically emits a distress call which alerts the emergency services and guides them to the scene. Depending on the accident type, the emergency call system is triggered either by the standard-fitted crash sensor in the S-Class that is also responsible for activating the airbags and belt tensioners, or by the rollover sensor.
The occupants can also send out the emergency call message manually with the aid of a button in the overhead control panel. Following the emergency call, TELEAID automatically establishes a voice link between the vehicle and the regional response centre. TELEAID is at present operational in Germany, Japan and the USA. It will be introduced succes-sively in other countries as well.
Three-Valve Technology
In emissions testing, the load at which large-volume six and eight-cylinder engines operate during warm-up is insufficient for them to be able to attain high exhaust temperatures quickly. Thus there is a delay before the catalytic converter is able to operate at full efficiency. This design-inherent phenomenon can be prevented by further reducing the heat loss which occurs between the combustion chambers and the catalytic converter. One way this can be achieved is by means of three-valve technology, as used by Mercedes-Benz on all S-Class petrol engines. Dispensing with one exhaust port reduces the heat loss from the exhaust stream so that the catalytic converter reaches its operating temperature some twelve seconds sooner following a cold start.
Throttle-Body Fuel Injection
A form of electronic fuel injection in which the injectors are centrally located in a throttle-body housing that contains a valve to regulate air flow through the intake manifold. Less efficient and precise than multi-port or sequential fuel injection.
Timing Valve
A valve in a fuel injection pump which times the delivery of fuel.
Toe-In
A wheel-alignment term that indicates the leading edges of a pair of wheels angle slightly toward each other. Front-drive cars are often aligned with slight toe-in to compensate for the effects of torque steer, or the tendency of the front wheels to pull to the side under hard acceleration.
Toe-Out
A wheel-alignment term that indicates the leading edges of a pair of wheels angle slightly away from each other.
Tongue Weight
The actual weight that is pressing down on the hitch attached to the vehicle. This weight should be subtracted to figure payload capacity. Typically, the tongue weight should be 9-11% of the trailer load. Too much tongue weight negatively affects the vehicle's steering, and too little tongue weight means the vehicle may lose traction.
Top-Fuel Dragsters
The fastest of drag racing vehicles, these have a characteristicly long body and use top fuel which accounts for the tremendous speeds these vehicles can attain.
Torque
A measure of twisting force, given in foot-pounds (abbreviated as lb.-ft.) or Newton-meters (N-m). In the case of an automobile, it is the twisting or rotational force the engine exerts on the crankshaft. Vehicle specifications often include the maximum torque an engine produces at a specific number of revolutions. An engine that produces 200 lb.-ft. of torque at 3,000 revolutions per minute, or 200 lb.-ft.@ 3,000 rpm, accelerates better at low speeds than an engine that provides 200 lb.-ft.@5,000 rpm.
Torque Converter
In an automatic transmission, a fluid coupling or electronic control that transmits power from the engine to the wheels. It allows the transmission to remain in gear while the vehicle is stopped. The fluid absorbs power and prevents the engine from stalling.
Torque Steer
The tendency of the front wheels on a front-drive vehicle to pull to the side under hard acceleration.
Torsion Bar
This is a type of spring made of a long solid tubular rod with one end fixed to the chassis and the other twisted by a lever connected to the suspension.
Torsional Stiffness
A vehicle body's resistance to twisting motions.
Towing
The maximum weight of a trailer that the vehicle can tow. Exceeding a vehicle's towing capacity may do serious damage to the engine and transmission.
Track
Vehicle width, measured from the center of one tire's contact patch to the center of the opposite tire's contact patch.
Traction Control System
Traction Control was developed in Formula One racing to control wheel spin as cars travelled through turns and on slick surfaces (oil) allowing consistent application of power and maintenance of control. The VSC system orchestrates the ABS and Active Traction Control (A-TRAC) sensors,actuators and computor electronics.
If a wheel loses traction, the computer will help minimize wheel slippage by controlling engine output and brake fluid pressure that is applied to the slipping wheel. Other system maintain control by Clamping down on the fuel supply to the engine (throttle), lowering engine power.
Typically the ABS is used to slow one spinning drive wheel, which sends power to the other as a limited-slip differential would. Then the engine power limiters kick in only if both drive wheels are spinning faster than the passive wheels, which indicates that both drive wheels have lost traction. Because the wheel-rotation sensors are part of any antilock braking system, cars equipped with traction control always have antilock brakes as well.
Traction control is like ABS for acceleration. If a wheel starts to spin, traction control may cut engine power or pulse the brakeon the spinning wheel (or perform both operations) to help transfer some of the engine's torque across the axle to the wheel with more grip. Expert off-road drivers sometimes pump the brake pedals on vehicles without traction control to try to accomplish the same thing. 4-ETS (four-wheel Electronic Traction System): Working with the vehicles'full-time four-wheel drive, 4-ETS uses individual wheel-speed sensors to detect the onset of wheel slip. Then it individually brakes the slipping wheels as needed, providing the effect of locking the front, center and/or rear differentials. The 4-ETS system continually balances the torque split to direct power to the wheel or wheels with traction.
Transaxle
A combined transmission and differential on front-drive vehicles.
Transfer Gearbox
A transfer gearbox (or transfer case) is a system of gears or an auxiliary transmission, used in four-wheel drive vehicles, which transfers torque from the transmission to the front and rear driveshafts. Transfer gearboxes typically have two gear ranges, High and Low. high Range is used for typical on-highway or light off-road use. Low Range is used for serious off-road conditions. Putting a transfer gearbox in "Neutral" disconnects the transmission from the wheels. Unless the brakes are applied (foot brake or hand brake), a vehicle can roll when the transfer gearbox is in "Neutral", even if the transmission is in "Park" (automatic) or a forward/reverse gear (manual).
Transmission
The gearbox that delivers power from the engine crankshaft to the drive axle or drive shaft. Most modern cars have a five-speed manual or a four-speed automatic transmission.
Tread-Wear Index
A tire rating consisting of a number followed by two letters, such as 300AB. The number indicates the useful life of the tire, the first letter (A, B, or C, A for best, C for worst) indicates its traction in wet conditions, and the second letter (A, B, or C, A for best, C for worst) its resistance to heat buildup.
Tri-Link Suspension
A fully independent rear suspension featuring a single fiberglass or composite leaf spring.
Trim Level
The level of options or features added to a model (Ford Mustand GT, Chrysler LeBaron XL).
Tune-Up
A regularly scheduled maintenance to check normal operation of the vehicle.
Turbine
An integral piece of the turbocharger, this small fan drives the compressor.
Turbo Lag
The time it takes the turbocharger to kick in after the driver accelerates; the lag results because a turbocharger compressor is spun by exhaust gases in the exhaust manifold.
Turbocharged, Turbocharger
Device that compresses and forces extra air into the intake manifold to produce extra power. Both turbochargers and superchargers are used to produce more power without increasing engine displacement, but neither are particularly fuel efficient and both can require costly maintenance as vehicles age.
Twist-Beam Axle
A semi-independent rear axle often used on front-drive vehicles. The horizontal beam, which connects the two rear wheels, can twist to reduce the effect of one wheel's motion on the other. Less expensive and more compact than fully independent suspension.
Twisting
Trying to induce a policyholder under false pretense to terminate an existing policy to take a new one.
Two-Seater
A vehicle that can only accommodate the driver and one passenger.
USAC
United States Auto Club, governs most auto racing in North America. An all inclusive organization that includes Indy Car, Sprint Cars, Silver Crown Cars, and midgets.
Understeer
Occurs when the front wheels have lost adhesion or the driver is turning the steering wheel too sharply for the vehicle's speed. In understeer, the front wheels do not follow the steering wheel angle, and the car refuses to turn and pushes ahead. In motorsports, this is called push. The driver can regain traction by reducing speed. Also may be called plow.
Unidirectional Tire
Tire whose tread pattern is designed to get optimum traction only when the tire is mounted to roll in one direction.
Unitized Construction
This is a type of body construction that does not require a separate frome to provide structural strength or support for the vehicle's mechanical components. A unitized body (or unibody)uses many strong but light structural elements as an integral part of its construction.
Universal Joint
A U-joint "connects" two moving shafts that aren't necessarily in a straight line. Depending on its design, a universal joint can accomodate a large variation between the angle of the input shaft and that of the output shaft.
V-Type Engine
In a V-6, V-8 or V-12 engine, the cylinders are divided into two banks, each of which is angled away from the other at the top, forming a 'V.' Typically, this angle is 60 degrees on V-6 engines and 90 degrees on V-8 engines.
V6
A vehicle with six cylinders. The cylinders are divided into two banks, each of which is angled away from the other at the top, forming a 'V'. Typically, this angle is 60 degrees on V-6 engines.
V8
A vehicle with eight cylinders. the cylinders are divided into two banks, each of which is angled away from the other at the top, forming a 'V'. Typically, this angle is 90 degrees on V-8 engines.
Valve Train
The valves and camshaft(s) within an engine, and any parts attached to the valves, such as rockers and pushrods, to move them up and down.
Valves
Many overhead-cam engines, particularly multi-valve models, are described by the total number of intake and exhaust valves in the cylinder head. A 24-valve V-6 engine would have four valves per cylinder: two intake and two exhaust valves. A 16-valve V-8 engine has only the standard single exhaust and single intake valve for each of its eight cylinders.
Van
A box-shaped truck with a forward cab and a cargo area to the back bumper.
Variable-Assist Steering
A power-steering system that varies the amount of assistance it provides according to driving conditions. It provides maximum assistance at low speeds for maneuvers such as turning into a parking space or turning a corner after leaving a stop light. It provides minimum assistance at cruising or highway speeds to provide greater vehicle stability.
Vehicle Identification Number (VIN)
A seventeen-digit identification number, unique to each vehicle, which includes codes for the manufacturer, year, model, body, and engine specifications.
Vehicle Skid Control
Yaw sensors keep track of the direction in which the car is moving relative to which way the driver is turning the steering wheel. When the sensors detect understeer or oversteer -- conditions in which the car is not going in the direction the front wheels are pointed -- a computer takes over and applies brakes or controls power to one or both of the drive wheels, so that the car comes under control.
The system is programmed to respond to a wide variety of scenarios and is so selective that it can apply only the brake on one specific wheel if that's what is needed to regain control.
To one degree or another, the anti-skid systems used on other cars operate in much the same way. They have two or four yaw sensors, central processing computers that monitor steering.
Vented Disc Brakes
A seventeen-digit identification number, unique to each vehicle, which includes codes for the manufacturer, year, model, body, and engine specifications.
Viscous Coupling
This complex device, also called a VCU, relies on the characteristics of a special fluid inside it. It can act as a differential, as a means to restrict wheelspin or both. It consists of a small sealed canister filled with silicon fluid. Inside are two sets of slotted metal plates - one connected to a front shaft, the other to a rear shaft.
When there is a significant speed difference between the shafts, the metal plates spin in relationship to each other, heating up the silicon fluid which becomes thicker (more viscous). The thicker fluid slows down the metal plates, limiting the speed difference between the shafts, and thereby the slippage right-to-left or front-to-rear.
In effect, a VCU "locks" the shafts together (although not mechanically, as in a locking differential). When there is little or no speed difference between the shafts, the viscous coupling does no work. Range Rover, as an example, uses a VCU as a slip-limiting device in conjunction with its center differential. Lexus RX300 uses a VCU in place of a center differential.
VNT turbochargers
The turbochargers of the two S-Class CDI models electrically adjust the pitch of their guide vanes in accordance with the engine speed in order to use as much exhaust gas as possible for compressing the intake air and developing boost pressure. This type of design is known as VNT (variable nozzle turbine) turbo-charging.
The system ensures optimal control of boost pressure in all driving situations: at low engine speeds, the guide vanes reduce the cross-sectional area of the exhaust gas stream and boost pressure is increased; at high engine speeds on the other hand the cross-sectional area is increased and the turbocharger operates at a lower speed.
Thus in all situations, as much energy as possible is derived from the exhaust gas stream for generating boost pressure. Better cylinder charging and thus higher torque are further advantages of VNT turbochargers.
Water Pump
The pump that circulates coolant through the engine block, cylinder head and radiator. It is driven by the engine crankshaft.
Wheel Size
Determined by the diameter and width of the wheel on which the tire is mounted. A 15-inch wheel has a diameter of 15 inches. A 15 X 7 wheel has a 15-inch diameter and a 7-inch width.
Wheelbase
A mainstay in drag races, this refers to when the front end of car lifts up during a race. It is also known as a wheelie.
Winch
A winch is an externally mounted mechanical device consisting of a cable spooled onto a drum. It is used to pull heavy or bulky objects or to retrieve a vehicle that is stuck. The drum can be driven by the engine, by hydraulic power or electrically.
Windowbags
The standard-fitted windowbags on the S-Class consist of nine chambers with a total volume of approximately 12 litres per bag. Within 25 milliseconds of a side impact the windowbag, which is approximately 2000 millimetres long, inflates like a curtain between the front and rear roof pillars. The inflated bag provides a large protective surface at head level for both the front and rear passenger, regardless of passenger stature and seat position.
Under normal conditions, the windowbags are concealed behind the interior trim (roof frame, A-pillars and C-pillars). In the event of an accident, they force this trim inwards as they deploy. The windowbags are also activated, together with the belt tensioners, if the rollover sensor detects a rollover of a certain type.
Winston Cup
The creme de la creme of NASCAR racing, the drivers are going for all the marbles in this race that spans the entire season as drivers accumulate points at each of 31 events. The driver that accumulates the most points, not the most wins, becomes the eventual Winston Cup winner.
Xenon HID Adapative Forward Lighting with LED Pipes
A souped-up headlight that uses xenon gas for additional light. They produce ultraviolet and visible light, which causes better viewing of signs on the highway. The Cadillac CTS-V uses this technology.
Yaw
The rotation of the vehicle's body around its center point as viewed from above. When a vehicle enters a turn or makes a sudden lane change, it experiences a change in yaw. A yaw sensor in the ABS stability control system senses this change to determine if the vehicle is experiencing understeer or oversteer. If the yaw rate indicates a problem, corrective actions are taken to help keep the vehicle under control.
ZEV
Zero emission vehicle. The most restrictive emissions standard.