Automotive Glossary

Automotive components defined


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.


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.


Vehicles have two A-pillars, one on either side of the front windshield. The A-pillar supports the roof of a vehicle and is located in front of the driver.

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.


What it is: 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. How it works: 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. Customer benefit: Outstanding ride and handling, even on rough roads.


What it is: 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. How it works: 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. Customer benefit: Reduced vehicle lean when cornering and improved ride.

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.


What it is: 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. How it works: 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. Customer benefit: 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.


What it is: 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). How it works: 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. Customer benefit: Improves shift consistency and transmission durability and allows for shifting that is better suited to specific driver styles or operating conditions.


What are they: Smart restraints provide more consistent protection for people of different sizes and positions in various vehicle crash situations. Traditional safety belts and air bags are set up to provide protection for a range of occupants and conditions by deploying or restraining in a fixed manner. Advanced restraint systems consider variables such as occupant weight, seating position, safety-belt usage and vehicle deceleration to control belt forces and deploy the air bag optimally. Also, air bags would be designed to not deploy at unoccupied seating positions, where a rear-facing child seat is installed or when an occupant is out of the normal seating position (too close to the air bag). How they work:A combination of sensors provides the computer with information about occupant position, occupant weight and seat track position. Accelerometers provide information about the collision. The computer uses this information to decide which restraints should be deployed and in what manner. Special hardware would be required to tailor deployment of restraints: Variable deployment air bag actuators allow air bags to fill at different speeds and to different volumes. Safety belt pretensioners tighten the safety belt at the beginning of a collision. Safety belt load limiters allow the safety belt to extend with high loads during a collision. Customer benefit: Potential for increased safety and comfort, reduced repair costs.


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.

All-Wheel drive

All-Wheel drive is a four-wheel drive system that has no two-speed transfer gearbox. It operates similarly to full-time or permanent four-wheel drive, but does not offer Low Range capability for off-road use. This system was originally available in passenger cars, such as those from Audi and Subaru. Now, however, All-Wheel drive is being used in a growing number of sport-utility vehicles, such as BMW X5, Oldsmobile Bravada, and Ford Explorer.

Angle of Approach

When viewed from the side, this is the angle between the ground and a line running from a front tire to the lowest-hanging componenet directly ahead (usually the front bumper).This angle gives an indication of how steep a ramp a vehicle can negotiate without damage. It also allows the driver to judge a vehicle's ability to climb over rocks and logs without hitting- and potentially damaging- the front part of the vehicle's body or chasis.

Angle of Departure

In side view, this is the angle between the ground and a line running from a rear tire to the lowest-hanging component directly behind it, usually the rear bumper or trailer hitch. Similar to the approach angle, the departure angle indicates a vehicle's ability to drive off a ramp or obstacle without damaging the rear of the vehicle.

Anti-lock Braking System

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.

Automatic Stick Shift

What it is: 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. How they work: 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. Customer benefit: Fuel economy improvement with fun-to-shift convenience and shift mode flexibility.

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.

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.

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.

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.

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).

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 metres 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 metres, a reduction of 45 per cent.

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.


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.

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.


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.

Coil Spring

Used in a suspension system, a coil spring consists of a bar of resilient metal (usually a steel alloy) wound into a spiral form. It can be compressed repeatedly or extended without permanent deformation.

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.

Constant-Velocity Joint

A CVjoint is a type of universal joint, usually used between the front half-shafts and front wheels/spindles in a front-wheel drive or four-wheel drive vehicle. CV joints are engineered to tansmit torque more smoothly (compared with universal joints) as they move through two planes (i.e. up/down and to a certain degree, forward/backward). They are also less prone to driveline vibrations.

Constant-Velocity Joint

A CV joint is a type of universal joint, usually used between the front half-shafts and front wheels/spindles in a front-wheel drive or four-wheel drive vehicle. CV joints are engineered to tansmit torque more smoothly (compared with universal joints) as they move through two planes (i.e. up/down and to a certain degree, forward/backward). They are also less prone to driveline vibrations.

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.


This component of a frame (or subframe), usually placed transversly, connects to and strengthens longitudinal frame rails.

Curb Weight

The weight of an empty vehicle, without cargo and driver and passengers, but including maximum amounts of fuel, oil, coolant and standard equipment, including the spare tire and tools.


A differential transfers power (more accurately, torque) from the transmission or transfer gearbox to the axles/wheels, and allows the axles and wheels to turn at different speeds (so the vehicle can turn corners without drivetrain wind-up - the wheels on the outside of a curve turn faster and travel a greater distance than the inside wheels). While most differentials are mechanical gear-driven devices, sometimes a viscous coupling (VCU) or a multi-late transfer clutch pack (MPT) can act in place of a differential.

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.

Disc Brakes

This type of braking system consists of a disc or rotor that rotates at the same speed as the wheel to which it is attached, straddled by a caliper. The caliper contains brake pads, operated by small pistons, that squeeze against the surface of the disc to slow it down or stop it. Disc brakes operate more efficiently at high temperatures and wet conditions than drum brakes.


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.


The driveshaft transmits power from the transmission or transfer gearbox to the differential. A four-wheel drive vehicle has at least two driveshafts - one running to the front differential and one to the rear. Driveshafts are also known as propeller shafts or prop shafts.


Also called a powertrain, this term describes all of a vehicle's components that produce power and transmit power to the wheels - the engine, transmission, transfer case, driveshafts, differentials, axle shafts and wheel hubs. (See Powertrain)

Drum Brakes

A drum brake uses a drum-shaped (cylindrical) housing, usually made of cast iron, that is attached to the wheel and toataes with it. Inside the drum are curved brake shoes that are forced into contact with the inner drum to provide braking. Drum brakes are simple and generally effective, but less efficient than disc brakes under heavy use or when wet. In modern passenger vehicles, drum brakes are usually used on the rear wheels (in combination with disc brakes on the front wheels).

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 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 ESP® 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 ESP® 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.

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.

Final-Drive Ratio

This is the ratio of the gearset (usually the differential) that is farthest from the engine. A ratio of 3-54:1 means the driveshaft turns 3.54 times for every one turn of the wheels. Generally speaking, the higher the number, the better the vehicle's initial acceleration and pulling power. The lower the number, the better the vehicle's fuel economy. (See also Axle Ratio

Fuel Injection

A mechanical system to inject atomized fuel directly into the cylinders of an internal-combustion engine; avoids the need for a carburetor.

Full-Time Four-Wheel drive

This drive system offers both a two-wheel drive and four-wheel drive mode. Four-wheel drive can be engaged on dry pavement for normal on-road driving because this system uses some type of center differential. A typical full-time four-wheel drive system offers two-wheel drive, four-wheel drive auto and four-wheel drive Low. Virtually all full-time four-wheel drive systems also have a two-speed transfer gearbox.

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.


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.


Horsepower is a measure of the rate at which work can be done. Historically, it was derived from the ability of the average horse to life 100 pounds over 330 feet in 1 minute - or 1 horsepower.

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.

Independent Suspension

This describes a suspension system wherein each wheel on an axle is sprung separately and can react independently to bumps. A non-independent suspension uses a solid, beam or rigid axle to "connect" the suspension of two wheels. Both systems have advantages and disadvantages.


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.

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.

Leaf Spring

A leaf spring is a long, flat, flexible piece of steel (or a composite material) curved into an arc that bends when forces act upon it. Leaf springs, most often used in pickup trucks, usually mount a solid axle to a vehicle.

Limited-Slip Differential

This differential has a mechanism to limit the speed differences betweeen its two outputs (generally, between the two wheels on the same axle). A limited-slip differential ensures that some torque is always distributed to both wheels, even when one has very little traction.


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.

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.

Manual Stick Shift

What it is: 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. How they work: 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. Customer benefit: Fuel economy improvement with fun-to-shift convenience and shift mode flexibility. *Always wear your seat belts And Remember Never drive faster than your Angel can fly. Homepage Automotive Glossary Locate a Cardealer Look for a Used Car CARCLUBS and Events Email address protected by JavaScript. Please enable JavaScript to contact me. New Cars Reviews and Specs Car Insurance V.I.P. section Car Finance on a new car List your used car for Sale for FREE!!

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-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.


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.

Part-Time Four-Wheel drive

The most basic type of four-wheel drive system, part-time four-wheel drive operates in two-wheel drive mode (usually rear-wheel drive) all of the time on dry pavement. Four-wheel drive can be engaged only off-road or when the pavement is very slippery because this system forces the front and rear wheels to travel at the same speed. Using four-wheel drive on dry pavement can damage the drivetrain and cause extreme tire wear. Virtually all part-time four-wheel drive systems also employ a two-speed transfer gearbox.

Permanent Four-Wheel drive

As the name suggests, permanent Four-Wheel drive sends torque to all four wheels "permanently" (continuously), on or off pavement. There is no two-wheel drive mode, and the driver doe not need to determine when to engage Four-Wheel drive mode. Drive selections typically include Four-Wheel drive High and Four-Wheel drive Low. Most permanent four-wheel drive systems also have a slip-limiting device plus a two-speed transfer case. Land Rover Discovery Series II and Range Rover use permanent Four-Wheel drive.


This term describes an engine and transmission combination. (See also (See Drivetrain)

Push-Button Four-Wheel Drive

Both part-time and full-time Four-Wheel drive systems can be engaged electronically via a push button on the instrument panel. While this is convenient, it does not change the abilities and limitations of the basic system.

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 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.

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.


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.


Used mainly in rear suspensions to compensate for heavy cargo loads, air shocks — also known as air-adjustable shocks — have long been supplied attached to lengths of plastic tubing and the same type of valve you find on a car tire, for manual raising and lowering.


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.


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.


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.

Suspension Travel

This term refers to the amount of vertical wheel movement allowed by the suspension, from full jounce to full rebound.


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.


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.

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.


Torque is the amount of rotational effort exerted at the crankshaft by an engine. The unit of measure is a pound-foot, which represents a force of one pound acting at right angles at the end of an arm one foot long. Remember: "Torque gets it going, and Horsepower keeps it going." Torque is used for moving from a standing stop; such as pulling a boat out of the water. Torque is the force that throws you back in your seat when you stomp on the gas. Horsepower is used for things like towing a trailer over a distance. Horsepower also creates a vehicle's top-end speed.

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.


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.

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. *Always wear your seat belts And Remember Never drive faster than your Angel can fly. Homepage Automotive Glossary Locate a Cardealer Look for a Used Car CARCLUBS and Events Email address protected by JavaScript. Please enable JavaScript to contact me. New Cars Reviews and Specs Car Insurance V.I.P. section Car Finance on a new car List your used car for Sale for FREE!!

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).


A transmission is a gearbox (either manual or automatic) with a number of different ratios to match the engine's rpm and torque to various driving situations.

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.

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.

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.


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.


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.
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