Automotive glossary

4 Wheel Drive and Automatic

4MATIC is the name of a complex electronically controlled all wheel drive system developed and used by Mercedes-Benz on some of its models. All Mercedes cars featuring this system also have an automatic transmission in standard equipment and that's where its name is derived from (4-wheel drive and automatic transmission).

Originally developed together by Mercedes and Steyr-Daimler-Puch engineers, the system is now at its third generation but it's still based on a rear wheel drive chassis on most of the models. The system employs locking central and rear differentials to provide additional traction in slippery conditions or during off-roading. On the G-Klasse the system uses three locking differentials (front, central and rear).

4 wheel Electronic Traction System

Working with the vehicle's 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.


An expression used to describe a six-wheeled vehicle - two wheels in the front and four in the rear - that is driven by the rear four wheels.


An expression used to describe a vehicle equipped with six wheels that is driven by all of them.


Vehicles have two A-pillars, one on either side of the front windshield. The A-pillar usually supports the roof of a vehicle and is located in front of the driver. On convertible models it also represents the main roll-over protection, and is among the strongest body parts.

Acceleration Slip Regulation

ASR prevents the driving wheels from spinning unnecessary while on slippery surfaces, or when the power coming from the engine is too much for ensuring good traction (unnecessary wheel spin). It also improves directional control with better traction during high speed cornering. Developed by Mercedes-Benz in the 1980's, the system uses the ABS speed sensors to calculate if one of the driving wheels is spinning faster than the other and automatically actuates its individual brake sufficient enough for it to regain grip (or arrive at the same speed as the other driving wheel).

Acoustic Parking System

The Acoustic Parking System (APS) uses ultrasonic sensors installed at the rear as well as at the front of a vehicle to make parking easier. Using information from the sensors, a microprocessor calculates how far is the car from an obstacle. An intermittent warning tone or lights on a display are usually used to give the driver warning of an impending impact with any object caught by the ultrasonic sensors' sight.

Active Body Control

The active suspension system Active Body Control (ABC) was developed by Mercedes-Benz in an effort to combine active safety and handling with ride comfort. Using high-pressure hydraulic servos, a multitude of sensor and high-performance microprocessors, ABC adapts the suspension and damping settings to different driving situations.

Computer-controlled hydraulic servos are mounted in the spring struts between the coil springs and the body, and are used to develop additional forces which act on the suspension and damping to control the car's body motion on the horizontal. Designed to control body vibrations in a range of frequency of up to 5 Hz, ABC reduces to a minimum caused is designed to control body vibrations in the frequency range up to 5 Hz - the kind of vibrations typically caused by uneven road surfaces, braking and cornering.

Mercedes-Benz engineers have used passive gas-pressure shock absorbers and coil springs which can be tuned in real time and independently to provide a good ride quality no matter the road conditions. In its latest generation on the S, CL and SL-Klasse models, ABC virtually eliminates body roll and pitch when accelerating, braking or cornering. Like most active suspension systems nowadays, ABC has different preset settings which can be chosen by the driver at the flick of a switch.

Active Cornering Enhancement

A feature first found on Land Rover vehicles, the Active Cornering Enhancement (ACE) is a system that reduces body roll during cornering. A pair of accelerometers are used to detect the angle of body lean and to instruct the ACE computer to counteract these movements by applying pressure to the vehicle's torsion bars via actuators which are hydraulically controlled.

On the Land Rover Discovery, the ACE system can counteract up 1 g of lateral acceleration in less than a tenth of a second, thus helping the vehicle become more stable and responsive during hard cornering.

Active Front-lighting System

The Active Front-lighting system (AFS) can redirect the headlamp units individually on a horizontal direction during vehicle cornering. All is made in accordance with steering angle and vehicle speed, and is assisted by a computer which determines the angle it needs to rotate the headlamps. An early purely mechanical version of the system appeared in the 1950's on the Citroen DS.

Active Noise Cancellation

The Active Noise Cancellation system is designed to implement an acoustically adaptive algorithm that cancels the unwanted sound by generating an anti-sound (or anti-noise) of equal amplitude and opposite phase. The original sound and the anti-sound acoustically combine, resulting in the cancellation of both sounds, thus improving the acoustical comfort in the vehicle.

Active Roll Mitigation

Active Roll Mitigation (ARM) is similar with Land Rover's Active Cornering Enhancement (ACE). This system is also able to react when the vehicle becomes light on one side in a fast corner, only in a different way. The ARM system only uses the braking system to stabilize the vehicle, by providing very short brake bursts on individual wheels, following information gathered from rollover and ABS wheel sensors.

Active Service System

Engines are equipped with a microcomputer that monitors the aging of the motor oil via data transmitted by sensors and calculates an individualized maintenance plan for the engine. A digital indicator in the cockpit notifies the driver of the number of kilometers remaining before the next maintenance check.

All engines fitted in newer Mercedes' are equipped as standard with the Active Service System ASSYST, which registers the varying operating loads individually and takes these into account for scheduling engine maintenance.

On the basis of sensor-derived data such as oil level, oil temperature, coolant temperature, engine speed, road speed and engine load, a microcomputer calculates the actual load on the engine oil and works out a servicing schedule for the engine which reflects this and announces the driver.

Active Suspension Technology

The Active Suspension Technology is a definition for any suspension system which can modify its settings in real time to control body motion in response to any road abnormality or during cornering, braking or acceleration. These type of systems usually respond to inputs from either the road or the driver using different sensors. At least in theory, a vehicle equipped with an active suspension can provide both a comfortable and firm ride, thus keeping a perfect balance between smoothness and good road handling.

Active Tilt Control

The Active Tilt Control is a technology used by some SUVs belonging to brands from the Ford Motor Company. Like other similar systems, ATC is used primarily for controlling body lean while the vehicle is cornering. A mounted accelerometer gives a lateral acceleration signal to a control module, which in turn directs pressure from pumps to hydraulic cylinders that replace the stabilizer bar links. The hydraulic cylinders wind up the stabilizer bars, thus minimizing the vehicle's body lean during hard cornering.

Active Transfer Torque System

The Active Torque Transfer System (ATTS) is basically Honda's example of a Limited Slip Differential (LSD), since is also used to transfer as much as 80% of the engine torque to the outside driving wheel. By using information gathered from multiple sensors, including yaw rate, steering angle and lateral acceleration, ATTS can transfer torque to the wheel with the greatest traction.

Active Valve Control System

The Active Valve Control System (AVCS) is a variable valve timing engine technology used by Subaru. Using similar ideas as Honda's VTEC, the system squeezes the best performance from the engine while also minding emission standards. It works by varying the timing of the intake valves and adjusting the positions of the camshafts based on inputs from various sensors in the powertrain. This increases the power output especially on higher rpms without sacrificing fuel consumption.

Active Yaw Control

The Active Yaw Control is a Mitsubishi developed system that stabilizes the yaw moment during hard cornering. By simulating a torque differential between the right and left driving wheels, the AYC system on the Mitsubishi EVO models improves cornering performance and lateral stability on most surfaces.

Adaptive Air Suspension

Created by Audi engineers, the Adaptive Air Suspension is an electronically controlled air suspension system coupled with continuously adaptive damping. Originally an Audi A8-only feature, it is now available for the Q7 SUV also. Each of the vehicle's wheels have air suspension struts which are being electronically controlled by a central control unit which takes its data from sensors on the axles and acceleration sensors on the body.

Making necessary changes in milliseconds, the computer controls the damping force at each individual wheel, thus minimizing uncomfortable body movements when the car is braking, cornering or even driving off-road (in Q7's case).

Another advantage of the AAS system is the body self-levelling feature, making the vehicle's suspension height remain constant irrespective of the load it is carrying. Also, the Adaptive Air Suspension allows the driver to directly influence the suspension characteristics like height and comfort settings as individually preferred.

Adaptive Cruise Control

With the help of a laser or a radar sensor, the Adaptive Cruise Control (ACC) system recognizes preceding vehicles, calculates their speed and keeps the distance required by automatically acting on the brakes and/or engine power.

ACC can scan the area in front of the vehicle in order to determine the distance to the vehicle ahead. The information gathered by the sensors and/or radar is used to warn the driver if he/she is tailgating or to maintain an automatic safety distance to the vehicle by cutting engine power or activating brakes if necessary.

Some ACC systems can actually get the vehicle to a complete halt without any driver intervention in case they're detecting an impending impact with the object in front of the car.

Adaptive Damping System

The AIRMATIC suspension system from Mercedes-Benz combines the pneumatic suspension with an Adaptive Damping System (ADS), which can individually adjust the shock absorbers forces to match the vehicle's payload, the state of the road surface and even the driving style.

The system comprises of a steering angle sensor, three accelerometers on the vehicle body, the ABS speed sensors on each wheel and a brake pedal sensor. These constantly measure the lateral and longitudinal acceleration of the car during driving. From this data, the ADS Electronic Control Unit calculates the optimal damper setting for each individual wheel and transmits the signals to special actuator valves located on the gas-pressure shock absorbers.

These valves are able to switch between different preset damping characteristics during the blink of an eye, thus switching from comfort to sporty mode at the touch of a button.

Adaptive Transmission Control

The Adaptive Transmission Control system is found only on automatic and sequential transmissions and is based on a fuzzy-logic processor which can recognize individual styles of driving and adapts transmission shift parameters accordingly. It usually uses a microprocessor to read data from various sensors, and with the help of a complex algorithm it decides when to upshift or downshift.

It is very helpful especially since the fuzzy logic processor allows it to actually memorize the driver's driving habits or "learn" the environment conditions (for example, on slippery surfaces it will change gears more rarely).

Adjustable height shoulder belt

A belt that usually has an anchor point with assorted slot positions, allowing the car occupants to individually adjust the safety belt to fit their size and/or height.

Advanced Compatibility Engineering

The Advanced Compatibility Engineering (ACE) body structure is the name given to a passive safety technology available on most modern Honda vehicles. It is essentially a structure designed to disperse collision forces away from the passenger space inside the cabin in case of a crash. This is done while the damage to other vehicles involved is also minimized. This is accomplished by utilizing different grades of steel and also well thought crumple zones distributed around the passenger area.

Advanced Restraint Systems

Advanced Restraint Systems are a safety technology designed to improve the efficiency of safety items during a crash. A combination of sensors in the cockpit monitor everything from the occupant's height, the seating position, safety belt usage and the vehicle's deceleration to control the airbag deployment and the belt forces during a crash. The data gathered from sensors and accelerometers is gathered and provided to a computer which uses this information to decide which safety restraints (belt limiters and multistage airbags) should be deployed and with how much force.


Aerodynamics are a very important part of automotive design, since it singlehandedly can influence by a high margin factors like fuel consumption, noise levels, top speed and undesired lift forces experienced by any vehicle at high speed. A more streamlined car will have a lower drag coefficient, thus increasing its mileage, its top speed and also lower wind noise levels.

On the other hand, there has to be a balance between a clean aerodynamic shape that can also provide downforce at very high speeds. High performance cars use different types of spoilers, integrated bodykits and diffusers to create venturi effects and improve the vehicle's road grip. Almost all aerodynamic elements on modern cars were inspired by the aviation industry and are designed using wind tunnels and computer simulations.


The airbag is also called a "Supplementary Restraint System", and in short it consists of an inflatable bag or envelope which keeps the occupants from hitting any hard parts of the vehicle's interior during a crash. In case of a collision, cars equipped with airbags give a much better chance of survival for its occupants, but ONLY when seat belts are worn - hence the "supplementary" part.

The way it works is pretty simple in theory: in case of a sudden deceleration (such as a crash) accelerometers within the car's body trigger the ignition of a gas generator propellant to inflate a nylon fabric bag very rapidly (under 1 tenth of a second). The airbag has small vent holes on its side in order to allow the propellant gas to be slowly expelled from it just as the occupant pushes against the bag.

Most airbag equipped vehicles have several accelerometers and/or gyroscopic sensors to help sense various types of impacts. The different signals from these sensors are fed into a microcomputer which can determine the angle of impact and even the severity of the collision taking place. Depending on the result of these calculations, the airbags ECU will decide if the airbag deployment is necessary or not.

Airbag Electronic Control Unit

Airbag ECU
The Airbag ECU uses information gathered from deceleration sensors usually located in the crumple zones of a vehicle. Within just 15 milliseconds of any impact, the information is already processed by the ECU, therefore it can determine if there is really a need for airbag deployment, whether they should be triggered in stages (in the case of modern multistage airbags) or whether only the seat belt limiters should come into force or not.


Instead of a conventional suspension and damping system with coil springs and gas-pressure shock absorbers, some Mercedes-Benz models are equipped with AIRMATIC, a system which combines a pneumatic suspension with the Adaptive Damping System (ADS).

All of its components mainly consist of pneumatic lines, pneumatic suspension struts on all wheels, an air compressor, a central air reservoir, solenoid valves and actuators, a central ECU and various pitch and yaw sensors on the vehicle's body. Everything is connected via a CAN (Controller Area Network) databus and fed to a multitude of microprocessors which decide the suspension's behaviour during different driving maneuvers and road surfaces.

All Wheel Drive

Sending power to every one of the vehicle's wheels all the time, or only when needed, through active or non-active differentials or a transfer case.

All Wheel Steering

All Wheel Steering is a system that turns the rear wheels in the same direction as the front wheels to aid in high-speed cornering. Other similar systems turn the rear wheels in the opposite direction as the front to aid in low speed maneuvering and/or parking.

All-terrain vehicle

The term All Terrain Vehicle is usually used to describe small open motorized vehicles with three or four wheels that are designed for off-road use. The versions with four wheels are also called quad-bikes or just quads.

Angle of Approach

When viewing the side of a vehicle, the angle of approach is the angle between the ground and a line running from the front tire to the low est-hanging component directly ahead (which is usually the front bumper). The intensity of this angle gives an indication of how steep a ramp can the vehicle negotiate without suffering damage to its undercarriage.

Angle of Departure

When viewing a vehicle from its side, the angle of departure is the angle between the ground and a line running from the rear tires to the lowest-hanging component directly behind them (which is usually the rear bumper). Similar to the approach angle only backwards, the departure angle indicates a vehicle's ability to drive off a ramp or some other obstacle without damaging the rear part of its undercarriage.

Anti Skid Control

The Anti Skid Control (ASC) keeps the driving wheel spin within the optimum range during hard acceleration or on slippery surfaces. The system uses information taken from the ABS sensors which monitor the rotational speed of the wheels and can intervene by individually applying the brakes or even cutting the engine power to the driving wheels until the wheel spin is counteracted.

Therefore, regardless of how hard the driver presses the gas pedal, the ASC system intervening on the engine power and on the brakes controls the car's acceleration with maximum possible efficiency, ensuring that none of the driving wheels will spin excessively.

Antilock Braking System

Originally developed for aircraft braking systems in the first half of the twentieth century, the Antilock Braking System (ABS) is essentially used to improve stability during braking and in some cases it can even shorten braking distances altogether. Appearing in various mechanical forms before, the first modern electronic four-wheel ABS system was co-developed by Mercedes-Benz and Bosch.

In cars without ABS, during hard braking the wheels lock, thus making impossible for the car to be steered and the vehicle most likely skids into the obstacle the driver is trying to avoid. The ABS prevents wheel lock-up during braking maneuvers by using sensors which can determine if any wheel is slowing down more than the others and computer-controlled valves which can limit the pressure delivered to each brake cylinder on demand. The whole system is controlled via a master ECU (Electronic Control Unit).

Since the ABS constantly pumps the brakes during a braking maneuver the driver can concentrate on steering the car while applying constant pressure on the brake pedal, without fear of losing control of the car's direction. Also, while braking on uneven surfaces (left tires on gravel and right ones on tarmac, for example) the ABS can keep the car's stability under control.

Assisted or automatic parking

A number of car companies have started to offer automatic parking features on their models nowadays. In theory, as the vehicle equipped like this passes a parking spot, the system ascertains the dimensions of the available space and if any obstacles might be in the way. Once it has evaluated this sensory data, it automatically calculates the ideal parking maneuver and it either lateral parks itself or requires gas and brake pedal input form the driver. This is done by using parking sensors on every side of the car and a microprocessor wh  ich in some cases can also control steering, braking and acceleration during the parking maneuver.

Attention Control System

The Attention Control System (ACS) consists of a camera installed in the cockpit to monitor the driverÂ’s blinking movements. The development of this system is aimed at eliminating the risk of driver inattentiveness, by constantly keeping track of the frequency and duration of eyelid movement. If the computer connected to the camera perceives the driver to be at risk of sleepiness at the wheel, the system can warn him ahead of time. Similar technologies are currently being developed by Lexus, Mercedes-Benz and Volvo.

Audi Space Frame

The first generation of the Audi A8 is the first car with an aluminium body built according to the Audi Space Frame principle. The ASF is a high-strength aluminium frame structure into which the panels are integrated so that they also perform a load-bearing function. The main advantage of this solution, especially on a heavier car is the low weight combined with better stiffness. Audi engineers say that the A8 would weight at least 15% more if it had a comparable steel frame.

Aufrecht Melcher Grossaspach

AMG is short for Aufrecht Melcher Grossaspach, and is the tuning arm of Mercedes-Benz. The company was founded in 1967 by former Mercedes engineer Hans-Werner Aufrecht and his business partner Erhard Melcher in a small German town named Grossaspach. The name originated from each of the two partner's family names and the town in which they started the business.

Currently no longer located in Grossaspach, but in Affalterbach - AMG started off by designing and testing Mercedes-Benz racing engines and after a few years expanded their business into building bespoke road cars, also based upon the tri-star vehicles.

Until the mid '80's there were no official tie-ups between the two companies, but then AMG started to supply the Stuttgart brand with aftermarket alloy wheels and various styling products. Mercedes-Benz took a majority stake in AMG in 1999 and a full ownership in 2005, and has now transformed AMG into its in-house tuner.

Automatic Braking Differential

The Automatic Braking Differential (ABD) system was co-developed by Bosch and Porsche in order to counteract unnecessary wheel spin by one of the driving wheels. In essence, ABD is an electronic locking differential that uses the brakes and inputs from the Anti-lock Braking System sensors to simulate "the lock" of one of the wheels in case of hard acceleration or during a high-speed maneuver.

On most car models, the ABD does not substitute for a real locking differential, but is a supplementary system which provides better directional stability and more traction on less-than-ideal road surfaces by applying braking power to any slipping wheel during acceleration.

Automatic Climate Control

The Automatic Climate Control is an air-conditioning unit which can automatically set the temperature desired by the driver without being influenced by the outside temperature or other factors. The most advanced climate control systems nowadays use different sensors and can take into account outside temperature, the sun rays' intensity and even the angle on which they're setting on the car in order to automatically regulate the temperature requested by the driver.

Automatic Distance Control

The Automatic Distance control (ADC) technology is similar with the DISTRONIC system from Mercedes-Benz. It is in essence a combination between Cruise Control and a radar based speed control system. When activated, the speed control system can make the car keep a constant distance to another vehicle in front independent of driver input.

If the radar determines an impending frontal crash is unavoidable it emits a collision warning and then automatically slows down the car to avoid it. Newer generations are actually able to bring the vehicle to a full stop behind the car ahead if necessary.

Automatic Locking Differential

The Automatic Locking Differential improves handling during acceleration in curves or when one of the driving wheels is on a surface with a different grip coefficient than the others. In short, it ensures the best rotational speed for each of the driving wheels, thus preventing loss of the car's dynamics during evasive maneuvers or potentially dangerous situations like driving with a lateral set of wheels on a slippery surface.

This is done by "locking" both wheels on a driving axle together as if they were on a common shaft. This forces both wheels to turn in unison, regardless of the traction (or lack of it) available to either wheel individually, making it a very efficient solution for off-roading if found on an all-wheel driven vehicle.

Automatic Locking Retractors

Automatic Locking Retractors allow the safety belt to be pulled in one motion until fastened, then operates as a ratchet, thus preventing further extension. On most safety belts you will hear a faint clicking sound that indicates the belt is locked and ratcheting in. The Automatic Locking Retractors on belts help to keep the occupants in place in the event of a frontal collision or during hard braking.


An automobile is a self-propelled wheeled vehicle that carries its own means of propulsion and is used for transport on land.

Axle Articulation

Axle articulation is the ability of a vehicle's axle to move in a different direction vertically relative to the chassis or the other axle/s. Most American pick-up trucks have axle articulation as a standard feature to help on rough roads.

Axle Ratio

The axle ratio is the proportion between a vehicle's driveshaft rotation and its driving wheel axle. For example, a 3:1 axle ratio means that the driveshaft turns three times for every rotation of the driving wheels. By changing a vehicle's axle ratio, you may change its towing capacity, but this also depends on the engine's power, naturally.

Belt force limiters

The belt force limiter is located inside the inertia reel on the belt housing and consists of a torsion bar. When a force exceeding a certain level acts on the belt strap, the torsion bar produces a controlled reduction in the locking effect of the inertia reel. In other words, it automatically limits the stress on the occupants chest in the case of sudden braking or a frontal collision.

Bi-xenon headlamps

Bi-Xenon headlamps are actually normal xenon headlamps which use a single 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 total light.

Body roll

The leaning motion of a vehicle's body while turning into a corner. Also known as yaw angle.

Body-side steps

The bars you can step up onto on the side of an SUV or an off-roader, making entry and exit a little easier. They are mostly found on American cars.

Bottom-end power

The power that an engine produces at low revs (at the "bottom end" of the rev range).

Brake Assist System

This Brake Assist System (BAS), developed by Mercedes-Benz to shorten emergency stopping distances, takes over if a driver doesn't apply enough braking power in a critical situation. The system automatically develops maximum brake boost, thus reducing the actual stopping distance by a significant margin (according to Mercedes-Benz in-house tests, by almost 45%).

Brake caliper

The brake caliper looks almost like a normal measuring caliper and is part of the disc brake. When brakes are applied, hydraulic fluid forces the brake pads using one or several pistons in the calipers towards the discs, causing the discs to squeezed.

Brake Fade

Any type of brake gets heated up after repeated or hard use. Apart from ceramic or any other ceramic alloy disc, all brakes diminish their effectiveness after they get heated up. This is called brake fade.

Brake Force Display

Brake Force Display is a system developed by BMW for alerting tailgating drivers of a potential hazard in front of their vehicle. It works by increasing the intensity of the brake lights under heavy braking. The extra lighting is triggered only after the ABS sensors detect a rate of deceleration in excess of 5 m/second (emergency braking), but not under normal braking in order to avoid unnecessary illumination.

Brake Horsepower

Brake Horsepower is the imperial (or British) measure of an engineÂ’s horsepower, and it is about 0.98 out of a metric horsepower.

Brake Lockup

In braking, lockup describes the point at which a wheel stops rotating while the vehicle is still in motion. This mostly happens in emergency stopping situations on vehicles which do not have ABS (Anti-lock Braking System).

Brake pedal travel

The distance that the driver's foot has to push the brake pedal before achieving optimum braking.


The pillar situated between the rear side windows and the rear window, that supports the roof. It's the last roof supportive pillar on normal four door sedans.

Cab forward

A vehicle design that moves the front wheels out farther on a front-wheel drive vehicle, which in turn results in a longer distance between the front and rear wheels. This creates more passenger area up front, therefore increasing interior leg-room room and comfort.

Center Differential

A normal differential is used in cars to help power the drive wheels while allowing them to spin independently of each other during cornering (same power, different rotational speeds). In vehicles with four-wheel drive, a center differential is required because during a tight turn all four wheels are rotating with different speeds.

Receiving power from the engine through the transmission or the transfer box, the center differential regulates the power between the front and rear axles, thus allowing different rates of traveling.

Center high-mounted stop lamp

An extra rear brake lamp that's placed high inside or outside the vehicle, designed to give tailgating drivers an additional reaction time for avoiding a rear collision. The "third brake light" - the way it's sometimes called - is using LED technology on most vehicles.


The term "chassis" usually describes a vehicle's structural frame, on which the actual body sits, but this is only true on "body on frame" vehicles. In vehicles with unitized or "unibody" construction, the chassis comprises everything but the doors, hoods, engine and suspension elements.

Child-security locks

Rear door locks that are controlled by the passengers in front and are designed to keep children from exiting the vehicle prematurely.

Coefficient of drag

The drag coefficient (Cd or Cw) is measuring how much aerodynamic drag a vehicle has. The bigger volume of air a vehicle has to push out of its way while traveling, the higher its Cd value will be, thus requiring more power and fuel to sustain that speed.

Coil Spring

Used in a vehicle's suspension system, a coil spring consists of a spiral shaped bar of resilient metal (usually steel or steel alloy). While traveling, the spring can be compressed or extended repeatedly while retaining its flexibility and without permanent deformation.

Common Rail Diesel direct Injection

CRDi is the marketing name given by Hyundai-Kia to all of the common rail diesel engines powering their vehicles.

Common rail Diesel Injection

CDI (Common rail Diesel Injection) is the marketing name given by Mercedes to their modern diesel engines, which are using common rail injection technology. In essence, common rail is a development of the direct injection system. Conventional direct injection diesel engines must build up fuel pressure for each cylinder injection, whereas in CDI (and other common rail systems) the pressure is generated independently of the injection sequence and remains constantly available in the fuel line (on a common rail).

Acting as an accumulator or a separate reservoir, the common rail is usually situated above the cylinders and is distributing the fuel to the injectors and a high and constant pressure. Regulated by the engine ECU, special solenoid valves control the amount of fuel being injected in each cylinder. The biggest advantage of this system is the power and fuel economy induced by the efficiency of common rail over conventional injection systems.

Composite cross car beam

A member made of composite material that acts as an energy-absorbing device in the event of a collision, improving the vehicle body's stabilization during the crash.

Computer Active Technology Suspension

A Jaguar developed system, the Computer Active Technology System (CATS) uses a network of sensors to monitor the driver's driving style and road conditions. The adaptive shock absorber on each wheel is constantly tuned by a microprocessor that calculates what to do by gathering data from all the sensors.

Connecting rod

A steel, aluminium or other similar material which connects the piston to the crankshaft in a combustion engine.

Constant Velocity Joint

CV joint
A CV (Constant Velocity) or a homokinetic joint is a type of universal joint, designed to transmit power from a rotating shaft to a wheel through a variable angle but with a constant rotational speed. They are usually used between the front half-shafts and front wheels in a front or four-wheel drive vehicle. Some rear-wheel drive cars with independent rear suspension also use CV joints at the end of the axle half-shafts.

Continuously Variable Transmission

In essence, a Continuously Variable Transmission (CVT) is a type of automatic gearbox with an infinite number of gears situated between two values (a maximum and a minimum). One of the most common types of CVT consists of a steel or rubber belt and two conical pulleys. Unlike a normal transmission, which effectively has to choose between a given number of planetary gears, the CVT just varies the diameter of the conical inner surfaces on which the steel/rubber belt rides.

Most of them use either hydraulic pressure or spring tension to adjust the distance between the two pulleys. The main advantage of CVTs over conventional transmissions resides in their smoothness, since basically there is no interruption of power during the "shifting" maneuver. The main shortcoming is the amount of torque they can handle, which depends strictly to the material of which the belt is being made of. This can be neglected to a certain amount by designs which are using more complicated roller arrangements instead of belts and pulleys.

Control Trac

Control Trac is the marking name for a system developed by the Ford Motor Company. In essence it is a computerized non-permanent 4WD system that evaluates the road conditions with the help of various sensors, and it can automatically switch the vehicle from two to four-wheel drive whenever wheel-slip occurs.

Cornering Brake Control

Developed by BMW engineers, CBC (Cornering Brake Control) regulates the pressure individually in each wheel brake cylinder so that the car can brake optimally during a turn. In order to do this, CBC is using the ABS sensors to determine each wheel's rotational speed and will try to compensate the natural tendency of a vehicle to oversteer if braking during a turn.


A coupe (or coupé) is a two or four-seater vehicle with a fixed roof and only two doors. There is no globally accepted official definition for the term though. According to SAE (Society of Automotive Engineers) standards, a coupe is a fixed-roof automobile which has less than 33 CuFt (approximately 934 liters) of interior volume. Any car with a greater interior volume is technically called a two-door sedan, not a coupe, even if it has only two doors.


The crankcase is the housing which contains the crankshaft, primary driveshaft and gearbox.


The crankshaft is the part of the engine which translates the engine piston's linear motion into a more usable spinning motion. It is usually connected to a flywheel, in order to reduce the pulsating characteristic of the four-stroke cycle in the combustion engine and to the driveshaft consequently.


The crossmember is a metallic section bolted or sometimes welded across the frame of a vehicle, usually to "cover" the underside of the engine bay, in order to support the engine and/or the transmission in their place.


A crossover is a type of automobile which blends the main characteristics of at least two car segments. Most crossover cars nowadays bring together the versatility of a family car with that of an SUV.

Curb Weight

Curb weight is 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. In the EU legislation, curb weight means the cars has to be weighed with the reservoir filled at 90%, a 68 kg driver, 7 Kg of luggage and all the other fill ups made.


Damping is the motion of cushioning the vehicle's body movements in order to smooth the ride over bumpy roads and eliminate uncomfortable vibrations coming from the surface of the road.

Daytime Running Lights

Daytime Running Lights (DRL) are a new feature incorporated on some of the modern cars in order to insure better visibility for other drivers, which in turn would help prevent more crashes. They are usually comprised of normal high-beam headlamps with reduced intensity or low-beam headlamps and are deactivated the moment "normal" headlamps are turned on.


A differential is a device that can be used to do two mainly different things: either it can be used to transfer power from the transmission (or transfer gearbox in case of a 4WD vehicle) to the driving axle, or it can allow two wheels on the same axle to turn at different speeds, but using the same power.

Differential Lock

A differential lock (or diff-lock) literally locks out the differential action, thus forcing the torque to be split equally between two wheels or two axles. Transforming two axles to work as one or two wheels to rotate as if on a single axle can help increase traction in off-road terrain or in a straight line while accelerating hard.

Dinamic Stability and Traction Control

Dynamic Stability and Traction Control (DSTC) is a sophisticated stabilization system from BMW which combines the DSC (Dynamic Stability Control) with the Traction Control system, thus essentially offering skid-free driving.

Dinamic Stability Control

Dynamic Stability Control (DSC) is BMW's marketing name for the Electronic Stability Control, which uses the anti-lock braking and traction control systems to improve directional stability when cornering and intervening to help prevent or correct oversteer and understeer. Like any other stability control system, it helps the vehicle avoid skidding and loss of control by applying the brakes individually or by reducing the engine power.

Disc Brakes

Disc brakes are the most common and also most effective means of stopping a vehicle. This type of braking system usually consists of a disc that rotates at the same speed as the wheel to which it is attached, straddled by a brake caliper. The caliper contains brake pads which are operated by one or more small pistons that squeeze against the surface of the disc to slow it down or even stop it. Compared to the drum version, disc brakes operate much more efficiently at high temperatures and wet conditions, basically by having a more complete design.


An internal combustion engine's displacement is defined as the total volume of the cylinders. More specifically, since pistons move up and down cylinders, the volume is defined by calculating the total air and fuel mixture an engine's cylinders can draw during one complete engine cycle (one revolution of the crankshaft). In most countries it is stated in cubic centimeters, liters or cubic inches.


Derived from the words "distance" and "electronic", Distronic is an advanced cruise control system found in some high-end Mercedes-Benz models. The main difference between a conventional cruise control system and Distronic is that - apart from keeping the vehicle on a steady speed - the technology is also using radar sensors to automatically detect and adapt to the speed of the car traveling in front. In its latest version, Distronic can use the data from the radar sensors to automatically accelerate or even bring the vehicle to a complete halt in case it detects changes in the speed of the vehicle ahead.

Double Overhead Camshaft

DOHC is a valve train layout characterized by two camshafts within the cylinder head. This means that there are two separate camshafts for inlet and exhaust valves, unlike SOHC (Single Overhead Camshaft) layouts where a single camshaft operates both inlet and exhaust valves.

Double-pod cockpit

An interior design that has separate and symmetrical areas carved out of the dash for the driver and front passenger; a retro look common to early Mustangs and 1963-67 Corvettes.


Downforce is the phenomenon when air pressure is pushing down on a vehicle at high speeds, thus enabling more stability and better traction. It is usually achieved by the use of spoilers and aerodynamic ground effects.


The driveshaft (also known as propeller shaft or propshaft) transmits power from the engine through the transmission (or transfer gearbox in case of 4WD vehicles) to the differential.


Also known as the powertrain, the drivetrain describes all of the vehicle's components which are used to produce and transmit power to the drive wheels. In short, the engine, transmission, driveshafts, differentials and axle shafts are all part of the drivetrain.

Drum Brakes

A drum brake is made of a drum-shaped housing (which is usually out of cast iron) that is attached to the wheel. Inside the drum there are usually two brake shoes curved around the interior that are forced into contact with the inner drum. The contact of the pads with the inner section of the drum housing provides braking. Drum brakes are very simple and generally very effective, except under heavy or hard use and under wet conditions, which is why they are less and less common on modern cars.

Dynamic Brake Control

Dynamic Brake Control (DBC) is a BMW developed active safety system which improves brake effectiveness during emergency braking. Vehicles equipped with the system use sensors to detect the speed and force with which the driver applies the brakes and then send this data to an ECU. If the ECU calculates that the driver intends to do an emergency stop using the criteria gathered from the sensors it will provide the maximum amount of pressure in the brake cylinders, in order for the car to stop in the shortest distance possible.

Electronic Air Suspension

The Electronic Air Suspension System (EAS) automatically adapts damping and spring characteristics, along with the vehicle's body level to driving conditions and load changes.

Electronic brake force distribution

Electronic Brake force Distribution (EBD). It actually senses the weight in the rear of the car (trunk, rear seat, or even how much fuel is in the tank) and sends more force to the rear brakes accordingly. So you experience more effective, better balanced braking.

Electronic Control Module

Electronic Control Modules are subsystems consisting of microprocessors and assorted signal inputs and outputs which can control different components within a vehicle (ABS, airbags, radar systems etc.).

Electronic Control Unit

The Electronic Control Unit (ECU) controls the fuel injection system and the ignition timing of almost any modern engine. Gathering information from various input sensors (coolant temperature, barometric pressure and air flow speed), the ECU can determine the optimum settings for the injection and ignition timing.

Electronic Differential Lock

The Electronic Differential Lock (EDS) is a Volkswagen technology which was developed to substitute most of the attributes of a conventional differential. Instead of being a mechanical device which regulates the torque distribution between two or more drive wheels, EDS uses the ABS sensors to detect wheelspin and brake each wheel individually , thus creating the illusion of torque distribution. Due to the stress it can create on the brakes by hard use, the system only works up to speeds of approximately 25 mph.

Electronic Fuel Injection

Developed from the need of a better fuel atomization at the fuel intake, the electronic fuel injection (EFI) has practically replaced the carburetor and the mechanical fuel injection altogether. Relying purely on electronics that calculate how to blend and distribute a precisely measured amount of fuel and air mixture into each cylinder. This in turn makes for a much more efficient combustion process, leading to a better fuel economy and more power.

Electronic Stability Program

The Electronic Stability Program (ESP) was co-developed by Bosch and Mercedes-Benz and is now one of the most well spread active safety systems in the world. Even though it uses different names, depending on the car manufacturer, all ESP systems work basically the same. First, a central ECU gathers information from several sensors, including the ABS wheel sensors, a steering angle sensor, yaw rate sensor and lateral acceleration sensor.

Then, using this information the microprocessor calculates if the vehicle has started engaging in oversteer or understeer. If that is the case, the ECU automatically brakes each wheel individually in order to stabilize the vehicle. In other words ESP reacts only after a vehicle has started to skid/drift and tries to counteract the movement.

Electronically Controlled Automatic

ECA (Electronically Controlled Automatic) is an automatic transmission that has its shift timing controlled by an Electronic Control Unit , which takes into account various factors such as road conditions or whether the vehicle is pulling a trailer or climbing steep hill.

Emergency Brake Assistance

The EBA system from Mercedes-Benz is designed to make use of the best capabilities the ABS (Anti-lock Braking System) has to offer in the event of an emergency braking. Electronic Brake Assistance achieves this by detecting if a faster or harder than usual application of the brake pedal - such as under a panic situation - has happened and acts accordingly by providing the maximum amount of pressure into the brake cylinders, thus making the car enter the ABS zone faster and shortening the stopping distance by a very high margin.

Engine Braking

Engine braking is a technique of slowing down a vehicle without the help of brakes but by using the engine's own power. It is best done with a manual transmission, although automatics can also be up to the task, especially modern ones.

Exhaust Gas Recirculation

EGR is essentially a method of reducing NOx emissions coming out of the exhaust by recirculating a fraction of the engine's exhaust gas back into the intake manifold. Even though the expelled gas is coming out with a very high temperature it acts as an inert filler that actually absorbs heat during the combustion process, thus reducing the temperature reached in the cylinders.

Fire Prevention System

The Fire Prevention System (FPS) is designed to interrupt fuel delivery in the event of a collision, thus minimizing the risk of fire.

Four valves per cylinder

Four valves per cylinder are mostly used on DOHC (Double Overhead Camshaft) engines. Two of the valves are for the air-fuel mixture intake while the other two open to allow the exhaust gases out of each cylinder.

Four Wheel Drive

Four Wheel Drive is a system which transfers engine power to four wheels independently and is mostly found on SUVs and all-terain vehicles. By using differentials it can transfer almost any amount of power percentage to any of the four driving wheels.

Front-wheel Drive

Front-wheel drive (FWD) is a term use to describe a vehicle layout in which only the front wheels are powered.

Fuel cutoff

A computer-controlled shutoff to the fuel system designed to prevent drivers from over-revving the engine, since over-revving is a primary cause of engine failure.

Fuel Injection

Fuel injection is a mechanical or electronic system designed to inject atomized fuel directly into the cylinders or the of an internal-combustion engine. Essentially, it replaces the carburetor by being much more efficient, since the injection process is much better controlled.

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).

Gross Axle Weight Rating

The Gross Axle Weight Rating is the maximum amount of weight that can be supported by each axle, as prescribed by the manufacturer.

Gross Combined Weight Rating

Gross Combined Weight Rating (GCWR) is the maximum weight of a completely loaded vehicle and its trailer, as designated by the manufacturer.

Gross Vehicle Weight

Gross Vehicle Weight (GVW) is the total weight of a vehicle (with passengers, luggage, fuel, coolants and any options or accessories).

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

Ground clearance is the measurement from the lowest-hanging point under a vehicle (usually a differential, part of the suspension or the exhaust system) towards the ground. A high ground clearance allows a vehicle to drive more easily off-road or through heavy snow without damaging the underbody.


A half-shaft is an articulated, rotating shaft used in independent suspension systems to transmit power from a differential to a drive wheel.


Hardtop is an automotive term which usually describes a rigid (sometimes detachable or even retractable) vehicle roof.


A hatchback is a type of automobile layout, consisting of a passenger cabin which includes an integrated cargo space, accessed from behind by a hatch or a flip-up window - which is usually counted as a 3rd or 5th door. Hatchbacks are also often called three-doors (two entry doors and the hatch) or five-doors (four entry doors and the hatch) cars.

Hauling Capacity

The hauling capacity is the maximum amount of weight - including driver, passengers, options, accessories and luggage - that can be carried by a vehicle, according to the manufacturer.

High center of gravity

A vehicle with a high center of gravity will exhibit more body lean in turns and will be less stable, therefore making it more likely to roll over than a vehicle with a lower center of gravity.

Hight Pressure Diesel direct Injection

HDi is PSA Group's marketing name for their range of common rail diesel engines.

Hill Holder

Operating via the ESP (Electronic Stability Programme) longitudinal acceleration sensor when first gear is engaged and both clutch and brake pedals are pressed, the ECU maintains front brake calipers pressure for a few seconds after the brake pedal is released to eliminate the risk of rolling backwards and ensures a smooth getaway uphill.


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 carry a weight of 100 pounds over 330 feet in 1 minute, which became the equivalent measurement of one horsepower.

Hydraulic valve adjusters

Hydraulic pressure used to maintain valve clearance that eliminates the need for valve adjustment and minimizes maintenance; many V6 and V8 powered automobiles have hydraulic valve adjusters.

Independent Suspension

The independent suspension is a system where each wheel can be moved on a vertical axis without influencing the other, and can react independently to bumps on the road.


An inline-six (or straight six) is an engine configuration where all cylinders sit in a straight line across the crankcase, while all the pistons are driving the same crankshaft. Along the V12 and other similar layouts, it is the best naturally balanced engine configuration.

Instant Traction

Insta Trac is a GM marketing name for a 4WD system that gives a vehicle the ability to shift from four to two-wheel drive and vice-versa without stopping. In older 4WD vehicles with a transfer box the driver had to manually engage the hubs at each wheel.

Integrated Chassis Control System

The Integrated Chassis System (ICCS) is a General Motors technology that integrates brakes, steering, suspension and traction control, using electronic sensors for more precise handling. It is currently used in some Cadillac models.

Integrated child seats

Some manufacturers offer integrated folding child seats into the normal seats of their vehicles. When not in use, the child seats can be retracted into the normal seats, which are usually in the rear part of the vehicle cabin.


The intercooler is a device used to cool the air coming into the combustion chamber on turbocharged and/or supercharged engines. This is done because cooler air produces more power, and charged engines tend to heat the intake air while it's being compressed, thus decreasing its burn and combustion chamber fill-up efficiency. Most intercoolers have an air-to-air system, air-to-liquid system, or sometimes combination of both.

Internal balancer

The internal balancer is a gear-driven balancer that absorbs engine vibration for a smoother operation and enhanced reliability.


ISOFIX is the name of standardized child seat anchorages used by most car manufacturers. It defines the standard attachment points to be built into cars, thus enabling manufacturer compliant child safety seats to be quickly and safely secured into the car's rear seats. On cars with a front passenger airbag deactivation option, the ISOFIX is also available for the front passenger seat.


Jounce is essentially the opposite of rebound, and it refers to the motion of a wheel that compresses or pushes against its suspension and is at the upper limits of its travel.


Kompressor is the marketing name given by Mercedes-Benz to its supercharged engines and is also the German word for supercharger (or compressor).

Ladder Frame

Ladder frames are used in vehicles with body-on-frame layouts, and is usually shapped like a large metallic ladder. In recent years, only pickup trucks and certain SUVs are still using this chassis solution, while other types of cars have switched to unibody constructions.

Lane Departure Warning system

The lane departure warning system is a newly introduced safety technology in use by various manufacturers. Most LDW assistance features can identify a vehicle's position in relation to the road's lane boundary markings using cameras or laser sensors integrated into the vehicle. If the vehicle should deviate from between the lane on which is traveling the system sends out a warning to the driver before he would potentially go off the road.

Leaf Spring

Mostly used on pickup trucks and commercial vehicles suspension, leaf springs are long, flat and flexible pieces of steel (or a composite material) curved into an arc. Usually mounted on solid axles, they were a normal type of suspension spring until World War II on most automobiles, being gradually replaced by coil springs over time because of their better comfort potential.

Limited-Slip Differential

The limited-slip differential (LSD) acts just like any other differential, distributing power from the driveshaft to the drive wheels. The main difference is that LSD involves a mechanism which limits the rotation speeds between the two axle shafts it spins. In other words it ensures that power is always distributed to both drive wheels even if one has little or no traction. It is generally used on high performance cars to insure greater stability during turns and some sport utility vehicles.


LINGUATRONIC is Mercedes-Benz's voice recognition system. While at first it was only used for voice-operating the car phone, now it can be used to control the audio and navigation systems on some of their automobiles. It works by receiving the driver's instructions via a microphone and can even initiate an interactive dialog using preset voices. Its software is programmed with voice recognition algorithms which can define the individual peculiarities of each human voice it "hears". Therefore, LINGUATRONIC can adjust to many different styles of speaking and can also understand certain dialects.

Liquid-cooled engine

Transfers engine heat into coolant (water and antifreeze) solution. The coolant circulates through cavities in the cylinder block, head and crankcase. The hot liquid coolant is piped to a radiator that efficiently transfers heat to outside air. Liquid-cooled systems maintain more constant operating temperature than an air-cooled system.

Live Axle

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.

Low Emissions Vehicle

LEV is a US federal classification of vehicles which emit low level of emissions.

Lower Anchors and Tethers for Children

Lower Anchors and Tethers for Children (LATCH) refer to a standardized system for child seat attachment, required by US and Canada legislation to be used in new vehicles. in other parts of the world it is known as ISOFIX.


Lugging happens when an engine's rpm is below its power curve and is struggling to give motion to the vehicle. This usually happens when the car is going uphill in a higher gear, and can be prevented by downshifting, which will usually put the car back into its powerband.

Luxury Utility Vehicle

While not having an official definition, LUV (Luxury Utility Vehicle) is said to be the acronym for a pickup truck or SUV with a high specification body and interior, while downsizing their primary purpose (hauling or off-roading).

Manual Stick Shift

Manual stick shift is just another term to describe a manual transmission in the United States. Besides a clutch pedal, drivers of such equipped cars use a stick shaped gear lever to manually change gears.


Called "bubble cars" in the past, modern microcars are very small vehicles designed purely for city driving. Most of them have engines borrowed from scooters or use electric power, can only sit one or two passengers and are generally found in crowded cities.

Motor Slip Regulation

The MSR (Motor Slip Regulation) is a Fiat safety technology. If the driver changes down abruptly in conditions of poor grip, the MSR system activates, restoring torque to the engine in oreder to prevent skidding caused by locking the drive wheels.

Multi Purpose Vehicle

The MPV (an acronym for Multi Purpose Vehicle) is a multi-passenger vehicle based on a car platform with maximized interior space. They are usually used by families and range in size from compact cars to almost van-like dimensions.

Multi-link independent suspension

The multi-link independent suspension was developed in order to optimize wheel movement geometry. A wheel which is not constrained by attachment to an axle can move in a vertical, horizontal or perpendicular direction. To prevent the wheel from moving in any other direction but a prescribed path, multi-link independent suspension attaches the wheel to five or sometimes even six flexibly mounted links, that can limit the wheel's kinematic behaviour to just one degree of movement freedom - which is vertical movement.

Multi-Plate Transfer

A multi-plate transfer (or multi-plate clutch) is a set of several hydraulic clutches that are progressively engaged and disengaged to limit slip at the drive wheels. They can act either as a normal differential or a limited slip one (LSD). Most multi-plate clutches are microprocessor-controlled, using various speed sensors to determine when to engage or disengage the clutches. Some SUVs for example use a multi-plate transfer case in place of a center differential.

Nitrous Oxide

N2O (Nitrous Oxide, sometimes called laughing gas) is a non-flammable gas usually used in surgery and dentistry for its anesthetic and analgesic effects. The main reason for which is so famous though is because it was used in early motor racing and also the modern tuning and street racing scene for its properties as an oxidizer to increase the power output of engines.

Occupant Position Detection System

The Occupant Position Detection System (OPDS) uses sensors to calculate passenger height and position. If a child should lean into the airbag deployment path, the sensor will prevent the side airbag from deploying and subsequently injuring the passenger.


Overdrive is a term which describes a transmission gear that reduces the power output needed to maintain the driving speed, therefore improving fuel economy.

Part-Time Four-Wheel drive

Part-time four-wheel drive is the most common type of all wheel drive. It usually operates only in two-wheel drive mode and it can be switched to all-wheel drive whenever the situation requires.

By employing a center differential or a transfer box, these types of all-wheel drive systems can transfer power to either the front only, rear or to all the drive wheels, depending on the driver's wishes.

On older designs, the all-wheel drive mode had to be manually engaged and the vehicle had to be stopped in order for the (usually front) wheel hubs to be locked, but it can now be done from the inside of the vehicle and on some vehicles even while they're moving.

Permanent Four-Wheel drive

Permanent four-wheel drive systems send power to all four wheels in a continuous manner. There is no need for the driver to engage two or four-wheels drive mode, since all of the wheels are always powered.

Power curve (powerband)

The power output of an internal combustion engine forms a curve if charted on a graph, since the engine has different outputs at different rpms. This is called the power curve, or powerband. The power curve can be more abrupt, or relatively flat, depending on the power output along the rev range.

Power steering

Power steering was developed in order to reduce the effort needed to steer the vehicle. In other words, the driver can change the vehicle's direction with the help of an external power source that can assist this operation.

Most power steering systems employ hydraulic pressure and are operated using power from the engine, but in recent years, electro-hydraulic and even 100% electric systems have been introduced.

Some modern steering systems can provide a variable amount of assist, depending on the speeds at which the vehicle is moving, while others are even using the "drive-by-wire" technology, with no direct linkage between the steering wheel and the the wheels.

Power Train Electronic Control

The Power Train Electronic Control (PTEC) is the Aston Martin moniker for a system which controls the engine management, fuel-injection, ignition and other diagnostics. Employing a central ECU, the PTEC technology is capable of transmitting information between different electronic elements in the engine in microseconds.

Push-Button Four-Wheel Drive

In some modern part-time four-wheel drive systems the "all-wheel drive mode" can be engaged electronically by simply pushing a button somewhere on the instrument panel, thus relieving the driver of locking the wheel hubs manually.

Pushrods (or rods)

Pushrods are found only in OHV (Overhead Valve) engines. Essentially, they are metallic rods which are actuated by the camshaft in order to operate (open and close) via rocker arms the intake and exhaust valves.


quattro is Audi's trademarked name for their four-wheel drive system. Now at its fifth generation since it was introduced in 1980 (on the Quattro model, or Ur-Quattro as it is known), the quattro all-wheel drive system is a permanent one, without the possibility of switching from four to two wheel drive.

Since on most of Audi's vehicles since the '80's it was designed around a Torsen (torque-sensing) central differential, in case of grip loss on certain road surfaces it can distribute torque between front and rear axles depending on the grip level.

Rack-and-pinion steering

Delivering a more precise feel than recirculating ball systems, rack-and-pinion steering is a common type of steering mechanism on modern automobiles. In simple terms, it consists of two gears that convert rotational movement into a linear one.

One of the gears meshes with a rack (a toothed metal bar), which in turn is directly linked to the wheels via tire rods. By rotating the gear with the steering shaft, the circular motion converts into a linear one and moving the rack from side to side, therefore turning the wheels into the desired direction.

Ramp Break-over Angle

The ramp break-over angle measures a vehicle's ability to safely pass over a ramp without touching its underside. For the best break-over angle possible, a high ground clearance together with a short wheelbase are necessary.


Rebound is the opposite of jounce, so it's still a vertical motion of the wheel. In other words, when the suspension springs back from a jounce, the term used to describe this motion is called "rebound".

Recovery Strap

Used mostly in extreme off-roading, the recovery strap uses kinetic energy (in the sense of a bungee cord) to help free a mud stuck vehicle by linking it to another vehicle which has traction.

Road sensing suspension

Road sensing suspensions use various sensors to gather input about the vehicle's body movement and control the dynamics of the suspension via a central ECU and either hydraulic or air installations. Most of these types of suspensions were developed in order to ensure ride smoothness and reduce the effects of disturbances on the surface of the road.

Rocker arm

The rocker ram is only found in pushrod engines. It is in essence a small reciprocating metal arm that pivots to open and close the intake or exhaust valves when the camshaft raises/lowers the pushrod.

Roll Stability Control

The Roll Stability Control (RSC) is a safety system introduced on vehicles manufactured by the Ford Motor Company (mostly SUVs) . Since its integrated in the Electronic Stability Control, when a potential rollover situation is identified by the onboard sensors, the RSC will automatically and individually brake each wheel or even reduce the engine power, thus improving directional stability, which in turn helps to avoid a rollover.


The sedan is the most common configuration of a modern automobile. Sedans usually have four doors, although the term can be used to describe a two-door body also. Most of them have a three-box configuration, but two-box bodies are also common, mostly in Europe.

Semi-elliptic multi-leaf springs

Usually found on trucks and sport utility vehicles, this type of springs consists of arched steel leafs that are stacked together horizontally to form the foundation of the rear suspension.

Sequential turbochargers

Sequential turbochargers were created from the need to decrease spooling lag. Two or sometimes more turbochargers are put to work in sequence. Usually, a smaller one begins working at low rpms and the other(s) at higher rpms, thus improving the power delivery throughout the power curve, not only above a certain number of revs.


Most part-time four-wheel drive systems in the past required their drivers to stop the vehicle and manually lock the front hubs in order to engage the all-wheel drive mode. Modern systems now have automatic front hubs locking, which translates into the ability to "shift-on-the-fly" from two-wheel drive to four-wheel drive mode.


Shocks are used in most suspension systems to compensate for heavy loads and also to restrict and stabilize the rebound and jounce movements. On racing cars or in the aftermarket tuning world, the shocks can be tuned to give the car better handling.

Short Long Arm suspension

The Short Long Arm (SLA) is a rather common type of suspension, which uses upper and lower control arms of different lengths in order to control wheel camber changes during suspension movement (jounce and rebound.)

Single overhead camshaft

Single Overhead Camshaft (SOHC) engines use one camshaft per each cylinder head to operate both the intake and the exhaust valves.


The term "skidplate" is referring to a protective plate(s) put under a vehicle to protect certain components that are vulnerable (transmission, oil pan, fuel tank etc.).

Speed-rated tires

Speed-rated tires are certified for safe use at higher speeds, after extensive testing by the manufacturer.

Sport Utility Vehicle

The Sport Utility Vehicle (SUV) is a type of passenger vehicle which combines the carrying capacity of a station wagon or minivan with features like an increased ground clearance and all-wheel drive. At first they were derived from truck platforms but most of them are now using unibody construction for a lighter weight and better fuel economy.

Station wagon

The station wagon (also known as a wagon, or an estate) is an automobile body configuration similar in design to a sedan with an extended cargo area.


The strut is a suspension element used mostly on unibody car configurations, that combines the shock absorber's main function with the ability to support sideway forces.


A subframe is a separate smaller frame usually attached to a monocoque (unibody) vehicle and is used in order to "keep" the engine and the transmission attached to the body of the car. Other types of subframes are used to attach the suspension to the vehicle's unitized structure.


The supercharger (also known as a blower in some countries) is used to compress air into the cylinders of an internal combustion engine. It works just like the turbocharger (increasing volumetric efficiency in the cylinders) except it's not powered by the exhaust gases but by belt or chain-drive from the engine's crankshaft.


The supermini (keicar in Japan and sub-compact in the US) is a class of automobiles that covers the smallest cars. They usually have a hatchback configuration and are designed specifically for city driving.

Supplemental Restraint System (airbag)

In order to reduce the driver/passenger's impact with hard parts of the interior of a vehicle in the event of a collision, the Supplemental Restraint System (SRS) causes an airbag to instantaneously inflate and supplement the seatbelt.

Suspension Travel

The term suspension travel is referring to the amount of vertical movement of a wheel along its vertical axis allowed by the suspension, from full jounce to full rebound.


The swaybar is a suspension element which comprises of a long torsion bar mounted between two wheels on the same axle. Also called an anti-roll bar or a stabilizer bar, it can restrict the body sway of the vehicle during cornering by transferring force and lateral movement from one wheel to the other.


The tachometer is essentially a gauge that can display an engine's revolutions per minute (rpm or revs).


The TELEAID is a Mercedes-Benz optional feature based on a built-in telephone. Essentially, it can emit an automatic distress call to alert emergency services in the case of an accident. Depending on the type of accident or vehicle, the system can be triggered by the crash sensors which usually activate the airbags and/or belt tensioning devices or by the rollover sensor.

Three-valve technology

Some car manufacturers (mostly Mercedes-Benz in recent years) have dispensed with one of the exhaust valves in their large V6 or V8 DOHC engines in order to reduce the heat loss from the exhaust, thus helping the catalytic converter to reach its operating temperature sooner and improve the engines' emissions.

Tire Pressure Monitoring

Tire Pressure Monitoring (TPM) systems were developed as a safety measure, and are using wheel mounted sensors to continuously check all tires for any changes in pressure and informing the driver via a display on the dashboard or instrument panel.

Tire Pressure Monitoring Systems

A comfortable system for tire pressure monitoring detects even small pressure fluctuations, locates the affected tires and informs the driver with warnings of varying urgency.

Tongue Weight

The tongue weight is the actual force that is pressing down on the front axle of a vehicle and is strictly related to mass distribution between the axles.


Torque (also called couple) is a vector that measures the amount of rotational effort exerted at the crankshaft by an engine. The unit of measure is a pound-foot in the US and UK (and other Imperial system using countries), and Newton meter by metric system standards (specifically Europe).

Torsion Bar

The torsion bar is a type of tubular rod or beam that has one end fixed to the chassis or body of the vehicle (in case of a unibody construction) and the other is twisted by a lever which is connected to the suspension. Currently, only certain American trucks and truck based SUVs are still using torsion bars suspension systems.

Towing weight

This term describes the maximum weight of a trailer or boat that a vehicle can tow according to manufacturer imposed standards.


The track is a term which describes the distance between two wheels on the same axle.

Traction Control System

Developed to minimize wheel slippage through turns and low grip surfaces, Traction Control works by using the ABS wheel sensors to detect if any of the wheels is spinning uncontrollably and individually brake it or even reduce engine power until the grip is restored.

Transfer (gear)box

A transfer gearbox (or transfer case) is a system of gears used to transmit power coming through the transmission to the front and rear driveshafts. Used in four-wheel drive vehicles, transfer boxes usually employ only two gears - low range and high range - which are used mostly in off-road conditions.

Transmission (gearbox)

The transmission (also called gearbox) is a gear-changing assembly which consists of a number of gears and other associated parts and it is used to transfer the power from a vehicle's engine to one or more driving axles.

Turbo Diesel direct Injection

TDI is Volkswagen's AG trademarked moniker for their Turbo Diesel direct Injection engines. While in the beginning they were all direct injection engines, now common rail ones also bear the same name in the VAG group.


Designed to improve the volumetric efficiency of an internal combustion engine, the turbocharger is a forced induction device which can increase an engine's output. It is essentially a turbine driven by the exhaust gases which sucks in air and forces it into the cylinders, unlike the supercharger, which is mechanically driven by the engine's crankshaft.

Two Wheel Drive

This expression is used to describe a vehicle with only two wheel drive. The first figure is the total number of wheels, and the second is the number of driving wheels. In some countries it's essentially a different name for rear-wheel drive vehicles (RWD), unlike 2X4, which can be used for describing a front-wheel drive vehicle (FWD).

Two-wheel drive

Two-wheel drive (or 2WD) is referring to any vehicle in which the drivetrain is sending power from the engine to a single axle (to only two wheels). Two-wheel drive vehicles can be either FWD (front-wheel-drive) or RWD (rear-wheel drive), and each has its advantages and disadvantages.

Unified Chassis Control

The Unified Chassis Control (UCC) is a Delphi technology which integrates different safety systems under the same umbrella in order to provide enhanced vehicle control. By integrating systems like the ABS, stability control, traction and even suspension control under a single ECU, the Unified Chassis Control can respond better to unforeseen driving situations.

Unitized Construction

A unitized (also called unibody or monocoque) body integrates the chassis and other structural elements into the construction of the vehicle, and does not require a separate frame or chassis to provide rigidity to the body, thus reducing the total weight.

Universal Joint

Designed to transmit a rotary motion between an output shaft and an input shaft with a different angle between them, the U-joint (or Universal) is comprised of two rods (or shafts) connected via a pair of hinges.


A valve is a device that regulates the flow of gases in and out of the cylinders of an internal combustion engine. Intake valves allow the air and fuel to enter the combustion chamber, while exhaust valves allow the burned gases to exit after combustion.

Variable Nozzle Turbine

Variable Nozzle Turbines (VNTs) have electrically adjustable guide vanes which can modify the boost pressure according to different engine speeds, thus counteracting the turbo-lag experienced by most turbocharged engines while increasing their power output and maximizing fuel economy.

Vehicle Dynamic Control

Vehicle Dynamic Control (VDC) is Alfa Romeo's marketing name for the Electronic Stability Programme, and is used to counter understeering and oversteering, thus improving vehicle stability during high-speed turns or on low grip surfaces.

Vehicle Skid Control

Vehicle Skid Control (VSC) is Toyota's trademarked name for a version of the Electronic Stability Programme, which can assist vehicles from skidding (understeer and oversteer) and mantain control by individually braking each wheel and even reducing engine power to provide stability. Like all other similar systems, it uses the ABS sensors and a yaw sensor to detect if the vehicle is out of control and acts accordingly.

Vehicle Stability Assist

Vehicle Stability Assist (VSA) is Honda's trademarked name for a version of the Electronic Stability Programme, which can assist vehicles from skidding (understeer and oversteer) and mantain control by individually braking each wheel and even reducing engine power to provide stability.

Viscous Coupling

Viscous Coupling (VCU) can act either as limited slip differential (LSD) or as a central differential in some all-wheel drive vehicles. The device itself consists of two sets of alternating and perforated metal plates mounted in a sealed drum, which are engulfed into a silicone or similar liquid.

Each set of plates is connected to a propshaft, and can transmit or limit the power between the two shafts depending on the speed of the plates, which heat up the aforementioned liquid, thus modifying its viscosity. In turn, more or less torque can be transmitted between two axles or two wheels according to the individual speed of the axles (or wheels.)


Vortec is General Motors' marketing name for a group of engines which are particularly used in most of their trucks and truck based SUVs.

Weight-to-horsepower ratio

The weight to power ratio is the result of a vehicle's weight divided by the power its engine develops, thus enabling a measurement of performance.


Wheelbase is the distance between the front axle and the rear axle of a vehicle. Cars with a longer wheelbase are more stable at high speeds and provide better interior room, while cars with a shorter wheelbase have better city handling and are generally shorter.


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 in mud. The drum can be driven in a rotating motion by the engine itself, by hydraulic power or even electrically.

Windowbags (window airbags)

Like any other airbag, windowbags are designed to protect a vehicle's occupants in case of an accident. They are called windowbags because in the event of a side collision the occupants' heads are protected by the slim airbags which surround each lateral window within milliseconds of the crash.

X-Drive all-wheel drive system

X-Drive is BMW's trademarked name for the all-wheel drive system used on the X5, X6, X3, 3, 5 Series and other future series. Its latest generation employs a multi-plate clutch transfer box situated between the axes to direct the power split between front and rear wheels.

Not depending on the ABS sensors alone, like the previous generation, the X-Drive is now controlled by a central ECU which transformed the system from a reactive to an active one. In other words, if just one of the wheels starts slipping the ABS sensors detect it and send the gathered data to the ECU which in turn commands the wet multi-plate clutch trough a high speed electric servo-motor which turns an actuator shaped like a disc.

In normal driving mode, the system splits the torque with a 38% - 62% distribution ration between the front and rear axles, but depending on driving conditions it can send up to 100% to a single axle.

Xenon High-Intensity Discharge

High Intensity Discharge (HID) headlamps use the light of a plasma discharge arc to generate light. Each lamp contains a HID light source, electronic ballast, an optical reflector and lens, which can give the headlamps low or high beams by changing.


Yaw is the measurement of a vehicle's rotation around its central axis (its center of gravity.)

Zero-offset steering

Designed to minimize torque-steer on front-wheel drive cars during acceleration or braking with each wheel on a different surface, the zero-offset steering has a scrub radius of zero. In other words, the lateral forces that act upon the wheels during aforementioned situations are kept to a minimum and the vehicle's stability is improved.