Glossary of automotive terms

This glossary of automotive terms is a list of definitions of terms and concepts related to automobiles, including their parts, operation, and manufacture, as well as automotive engineering, auto repair, and the automotive industry in general. For more specific terminology regarding the design and classification of various automobile styles, see Glossary of automotive design; for terms related to transportation by road, see Glossary of road transport terms; for competitive auto racing, see Glossary of motorsport terms.

A
accelerator:

A in the form of a foot-operated pedal, or sometimes a hand-operated lever or paddle, by which the flow of fuel to the (and thereby the engine speed) is controlled, with depression of the pedal causing the vehicle to accelerate.

admission stroke: See.

aftermarket:

air brake: A type of in which the force that actuates the brake mechanism is provided by compressed air acting on a within a brake chamber or. Such systems are used primarily in commercial vehicles. An aerodynamic designed to retard high-speed vehicles.

airless injection:

A type of which relies on mechanical pressure only; the normal method of injection in a.

all-wheel drive (AWD):

alternative fuel vehicle:

alternator: A small electrical generator that converts mechanical energy into electrical energy in the form of alternating current, typically by using the to drive the rotation of a magnet which induces a current in a stationary armature. This electrical energy is then stored in the.

anti-lock braking system (ABS):

antifreeze: Any chemical, commonly ethylene glycol, that is added to the cooling water of an in order to decrease its freezing point for winter operation, when ambient temperatures may be below the normal freezing point of water.

articulated vehicle: Any vehicle consisting of two or more usually separable wheeled units, such as a towing vehicle (e.g. a tractor unit) combined with a towed vehicle (e.g. a or ) that is often unpowered and carrying a load. Articulation is primarily in the steering mode, though some degree of horizontal axis articulation is usually also necessary to enable the combined tractor-trailer to negotiate road surface irregularities.

automatic transmission:

automotive design:

automotive engineering:

axle: A horizontal transverse shaft or beam with spindles on which road wheels are mounted. There are many different types of axles, typically distinguished by their placement relative to the vehicle's center of mass and their intended use. Vehicles are often classified by the number of axles they possess.

axle ratio:

B
back-fire: An explosion of unburned or partially burned fuel that occurs in an or inlet system, rather than in the as intended.

backup camera:

ball and socket:

A type of mechanical joint in which a spherical end (the ball) moves freely within a recessed cavity of the same shape (the socket), commonly used in and linkages.

battery:

bell housing:

bench seat:

body-in-blue:

brake: Any device designed to apply friction to a moving or moveable surface in order to slow it, stop it, or prevent it from moving, especially one that slows, stops, or prevents the rotation of one or more of the wheels of an automobile. Most wheeled vehicles are built with at least one brake for each wheel, which can be applied either independently of each other or, in four-wheeled vehicles, all at the same time, by depressing one or more foot-operated or. If the vehicle is already in motion, the act of applying the wheel brakes, known as braking, will ultimately cause the entire vehicle to slow or stop as the friction generated by the contact between the tires and the ground overcomes the vehicle's inertia. If the vehicle is stationary, the same brakes or a separate brake may also be applied to prevent the wheels from rotating while the vehicle is parked. There are many types of brakes which operate on a wide variety of physical principles. Modern automotive rely on a large and complex network of precisely controlled mechanisms in order to deliver optimal  for specific road conditions, to prevent brakes from  and overheating, to reduce the amount of input required from the driver, and ultimately to maximize safety, efficiency, and durability.

brake balance:

brake dive: See.

brake fade:

brake fluid:

brake light:

brake pad:

brake pedal:

brake puck: See.

brake shoe:

brake swept area:

brake rotor:

braking distance:

braking system:

breeches pipe: See.

bucket seat:

bullbar:

bumper:

C
caliper:

In a system, the mechanism that brings the to bear on disc by a clamping or pinching action.

camber angle: The angle between the plane defined by the circumference of the wheels and the vertical axis of the body or of a vehicle, as viewed from the front or rear of the vehicle. If the top of the wheel is tilted outward, away from the body, the wheel is said to have positive camber; if the top is tilted inward, towards the body, it is said to have negative camber. Angled wheels are sometimes an intentional part of a vehicle's design, but most ordinary road vehicles are intended to have minimal or neutral camber (i.e. the wheels are completely parallel to the body and perpendicular to the road surface).

carburetor:

carputer:

caster angle:

The angular displacement of the from the vertical axis of a steered, as seen from the side of the vehicle.

catalytic converter:

center cap:

center console:

chassis:

The structural lower part of a vehicle to which the and are attached, or more generally the main load-bearing framework which supports all of a vehicle's mechanical parts and other components and on which the body is mounted. Compare.

choke:

A valve that restricts the amount of air entering an on the, thereby enriching the fuel-to-air ratio for ease of starting and running, especially when the engine is cold.

clearance volume: The volume remaining in a above the when it reaches. See also.

clocking: Illegally tampering with a vehicle's reading.

clockspring:

clutch:

cold cranking amp:

cold inflation pressure:

combustion chamber: The part of an in which combustion occurs; in particular the space within a bounded by the top of the  when at  and the  in a reciprocating engine. Since most of the fuel/air mixture's combustion takes place in this space, its volume, shape, and design greatly affect the power,, and of the engine.

compression ratio: The ratio between the maximum and minimum combined volume of an internal combustion engine's and.

continuously variable transmission (CVT):

coolant: Any substance, usually a liquid, that is circulated around a vehicle's engine in order to reduce and regulate temperature by absorbing excess heat and then transferring it to another medium (e.g. the surrounding air) where it is safely and efficiently dissipated. An ideal automotive coolant has high thermal capacity, low viscosity, and is chemically inert and non-toxic; though specific properties can vary widely by intended usage, most ordinary personal vehicles use water as the base coolant with additives such as ethylene glycol or methanol to lower its freezing point, raise its boiling point, and prevent corrosion.

cornering:

cowling:

crankcase: The housing that surrounds the.

crankshaft: A linear shaft that translates reciprocating motion created by the of an engine into rotational motion via a series of "crank throws" or "crankpins" – additional bearing surfaces which are slightly offset from that of the shaft and which are attached to the connecting rods of the pistons. The crankshaft is often attached to a and vibrational dampers to reduce the pulsation characteristic of  and other undesirable movement.

crankshaft journal: The part of the that rotates in a main bearing, with connecting rods attached to the engine's pistons.

crankshaft throw:

The lateral distance between the centerline of the and the furthest offset of a big end, equivalent to half the length of a stroke; i.e. the distance by which the journals are offset from the main shaft.

crossfiring:

crossflow cylinder head:

crossmember:

curb weight: See.

D
dashboard:

differential: A system of gears capable of dividing the input torque of one shaft between two output shafts where the two shafts are likely to rotate at different speeds, as in. The differential is used as the final drive of vehicles with two or more.

dipstick: See.

disc brake:

dispersant:

A additive which separates and holds solid or liquid contaminants in suspension, preventing their settling or clumping and thereby reducing deposition in the engine.

displacement: The total volume swept by all of the in all of the of an, excluding the volume of the. Engine displacement is commonly used as a measure of an engine's size, and by extension as an indicator of the power the engine is hypothetically capable of producing and the amount of fuel it can be expected to consume.

displacement factor: An index of vehicle performance usually expressed as the product of the and divided by the product of the   and the vehicle's.

dive: The dipping of a vehicle's front end that occurs when the are applied. Dive is caused by a load transfer from the rear to the front, as the inertial force of forward motion passes through the vehicle's center of gravity, which is higher than the points where the braking forces are exerted on the ground.

donut: See.

drive axle:

The or axles used to transmit from the, imparted via a, to one or more ; a driven axle.

drive shaft:

The shaft or shafts by which mechanical power and torque is transmitted from the rest of the to a (and hence to a  and ).

drive wheel: The wheel or wheels used to transform from the into tractive force, and to transmit that force from the tires to the road, overcoming stationary forces and causing the vehicle to move forwards or backwards; i.e. the wheels that are driven, as opposed to merely rolling under the momentum imparted to them. Vehicles may have any combination of driven wheels; power applied to the two front wheels or two back wheels is (2WD), and power applied to all four wheels is  (4WD). Which wheels are driven is variable in (AWD).

drivebox: See ' and '.

drivetrain:

All of the components of a motor vehicle that are involved in delivering power to the, excluding the or motor that generates the power. The drivetrain typically includes the (if present),, , , and one or more. Contrast.

drop arm: See.

drum brake:

dry clutch:

dynamometer:

E
econometer: An instrument that measures and displays instantaneous fuel consumption or.

economizer:

Any device or system designed to reduce fuel consumption by preventing unnecessary energy expenditure or by repurposing energy that would otherwise be wasted to perform useful functions. The term commonly refers specifically to a system that automatically modifies the ratio of the supplied to the engine in order to save fuel when at constant speed.

electric vehicle:

electronic control unit (ECU):

engine block: The structure, typically cast in one piece, which contains and houses the,, and other components of an. Modern engine blocks usually also have an integrated, as well as passages and.

engine configuration:

exhaust manifold:

exhaust system: The assembly of parts that conveys the gaseous products of the 's combustion reactions (collectively known as exhaust) out of the combustion chambers, away from the engine, and ultimately into the atmosphere. In the most basic design, exhaust gases flow from each of the heads into an and then through one or more, which expel their contents behind, above, or to the side of the vehicle. In modern systems, the exhaust may also flow through a, various control devices (e.g. a ), and/or a  and  (to reduce noise and vibration) before exiting through one or more.

F
fan belt: The endless that transmits rotational motion from the engine to the.

fender: The fixed part of a vehicle body exterior that frames the, with the primary purpose of blocking sand, mud, rocks, liquids, and other that is thrown into the air by the rotating ; or any deflector plate or structure mounted at the front or rear of a vehicle near ground level. A fixed that partially shrouds a tire from view and similarly serves to deflect road spray.

fifth-wheel coupling:

firing order: The numbered sequence in which the of a multi-cylinder are ignited.

flat engine:

flathead engine:

footprint: The shape of the contact interface of a loaded with the ground. See also.

footwell: The lower interior part of the, which accommodates the feet of the driver and the front passenger, as well as the and often other control features on the.

four-stroke engine:

four-wheel drive (4WD): A system in which torque generated by the engine is delivered simultaneously to all four of a four-wheeled vehicle. Thus all four wheels are, as opposed to, in which only one pair of wheels receives power at a time (either the front or rear wheels). Four-wheel drive can provide greater when road conditions are suboptimal, but typically has negative effects on  and  at speed. It may be either permanent or selectable on-demand; in the latter case it is often referred to as.

frame:

friction clutch: A type of in which torque is transmitted by pressure of the clutch faces on each other.

front-wheel drive (FWD): A system in which torque generated by the engine is delivered only to the two  at the forward end of the vehicle, as opposed to  and distinct from.

G
gas pedal: See.

gearbox:

gear stick:

glove compartment:

A compartment built into the of an automobile above the front-seat passenger's, often used to store miscellaneous items such as small tools and paperwork and, traditionally,. The compartment usually closes with a latch and in some vehicles can be locked with a key.

glow plug:

governor:

A device which limits the maximum rotational speed of an, usually by controlling the fuel supply, in order to prevent mechanical damage, overheating, or unacceptable levels of. They are used primarily in.

gradeability: A measure of the ability of a vehicle to ascend an incline of a specified grade.

grille: A grid or grating covering an opening in the body of a vehicle and allowing air to pass through it, especially an ornamental one at the front end of a vehicle designed to ventilate the and engine compartment.

gross axle weight:

The specified maximum carrying capacity of an, as measured at the tire–road interface.

gross power: The total measured power output, typically expressed in watts or, of an intact, unmodified operating in optimal conditions without the burden of any power-absorbing auxiliaries such as electric generators, pumps, or silencers.

gross train weight: The total combined weight of the and of a commercial vehicle.

gross vehicle weight (GVW): The maximum total weight at which a vehicle can be legally operated, including the plus the weight of any payload.

H
handbrake: Any operated manually by a hand lever, but especially a.

handling:

headlamp:

headlight:

heat soak:

hidden headlamp:

hood:

The hinged cover over the compartment of a motor vehicle. Hoods can be opened to allow access to the engine and most other power and accessory components for maintenance and repair.

horsepower (hp):

hub:

hubcap:

hybrid vehicle:

I
idle port: An opening in the body through which the dispenses fuel while the engine is, i.e. while the throttle is otherwise fully closed.

idle speed:

The rotational speed of an unloaded engine at the minimum setting.

idler arm:

idling: Running a vehicle's engine while the vehicle is not in motion, without any loads except the engine accessories, e.g. while waiting at a traffic light.

ignition coil:

ignition switch:

inline engine:

An layout in which all are aligned in one row without any offset, i.e. in a single plane of the  axis. Inline layouts tend to be simpler in design and easier to build than or  layouts, smaller in physical dimension, and more broadly compatible with various engine designs because they can be mounted in any direction.

instrument panel:

intake manifold:

internal combustion engine:

J
jacking bracket:

jump lead:

One of a pair of heavy-duty electrical leads by which a vehicle with a discharged battery may be connected to an external source of power, such as a charged battery in another vehicle, in order to recharge the dead battery, a process known as a.

jump start:

A procedure of starting the engine of a vehicle with a discharged or depleted battery by using from a charged battery or other external power source.

K
kerb weight:

The total mass of an unladen vehicle including standard equipment and all consumables necessary for operation, including water,,, , , etc., and (sometimes) a full tank of fuel, but excluding passengers and cargo. The precise definition varies by location. Compare.

keyless entry:

kickdown:

A system that enables a driver to select a lower gear than the one automatically engaged by an, e.g. when accelerating rapidly, usually by depressing the pedal fully.

kingpin:

The vertical or inclined shaft about which a assembly pivots. The main fastening member between a and.

knock rating: See.

knocking:

knockout axle: A type of detachable, usually on a, the removal of which allows further lowering of the loading bed.

L
leaf spring:

lifting axle:

limited-slip differential:

locking differential:

longitudinal engine:

lugnut:

M
main drive belt: See.

make: The manufacturer of a particular vehicle.

manual transmission:

manumatic:

marque:

model: The specific style, size, and/or type of a particular vehicle produced by a particular manufacturer; the set of features and design elements which unify a particular class of vehicles produced by a manufacturer. See also.

moonroof:

motor oil:

Any of various viscous liquids used to lubricate the mechanical components of an, with the primary purposes of reducing friction and wear on moving parts, cleaning and preventing the accumulation of and, improving the static seal created by and , and cooling the engine by carrying heat away from the moving parts. Modern commercial motor oils typically consist of a mixture of base oils produced from crude petroleum and enhanced with various additives, including, , and other chemical protectants, which is then circulated under pressure through in the.

muffler:

multivalve engine: An having more than the conventional one and one  in each, a design intended to increase the flow of fuel-air mixture into the cylinders and of exhaust gases out of them.

N
nave: The hollow or dished center part of a road wheel on which the is mounted. The face of a road wheel that is bolted to the.

nave cap: See.

neutral (N): A position in which no gear is engaged, such that there is no transmission of torque between the input and output shafts of the. The neutral position effectively disconnects the between the engine and the wheels. Power may still be generated by the engine, but it cannot be delivered to the wheels; unless prevents it, the wheels of a vehicle in neutral are still capable of rotating in either direction under the momentum imparted by any external force.

north-south: Describing an engine layout in which the are arranged along the vehicle's longitudinal axis, from front to rear, as opposed to an layout.

noseweight:

O
octane rating:

odometer:

off-road vehicle: Any vehicle capable of or specifically designed for traveling on unpaved, uneven, and/or low-traction surfaces such as gravel, sand, mud, snow, rocks, or other natural terrain, especially a vehicle having, long, high , and specialized such that it performs well on these surface types, with lesser risk of being damaged or immobilized than an ordinary street vehicle.

oil filter: A filter designed to trap and remove particulate contaminants from,, hydraulic oil, or any other lubrication system.

oil gallery: Any space or passage within an,, or through which is intended to flow under pressure.

oil gauge: An instrument that measures and displays the instantaneous pressure and/or temperature of the circulating within a lubrication system, especially.

oil level indicator:

A long, flexible metal rod with graduated markings that is manually inserted into and then removed from the motor oil reservoir in order to give an approximate measure of the amount of oil in the reservoir.

oil pan:

oil pump: An electrically powered device which pressurizes and distributes to all parts of a lubrication system. When not otherwise qualified the term usually refers to the pump.

on-board diagnostics (OBD):

overdrive:

overhead valve engine (OHV):

overspeed governor: See.

oversteer:

P
parking brake:

A mechanism used to keep a vehicle securely motionless when parked, generally consisting of a cable connecting two conventional wheel (usually on the rear wheels) to a pulling mechanism in the vehicle's cab, typically either a hand-operated lever or handle located near the or a foot-operated pedal near the other pedals.

piston:

platform: A set of common design, engineering, and production efforts, as well as major automotive components, shared between a number of outwardly distinct vehicle models and even different vehicle classes which are often manufactured by different though usually related. Auto manufacturers commonly introduce new models based on existing platforms in order to reduce the costs associated with the development of entirely new products.

play:

Free movement or looseness within a mechanical system, especially when not intended by the mechanism's design, e.g. any motion of a before the respond by turning.

power locks:

power steering:

power stroke:

The of a reciprocating engine during which the is forced outward by the immense pressure generated by the combustion of fuel in the, typically considered to include that part of the cycle during which the piston moves from  to.

power windows:

powertrain:

powertrain control module (PCM):

R
rack and pinion: A type of linear actuator comprising a circular gear (the pinion) engaging a linear gear (the rack), which operate together to translate rotational motion into linear motion or vice versa: rotating the pinion causes the rack to be driven linearly, and driving the rack linearly causes the pinion to rotate. Rack-and-pinion mechanisms have been employed in many different automotive systems and components, as in.

radiator: A heat exchanger that serves to cool the by pumping spent (previously heated by the engine) through a system of tubes which are then exposed to relatively cool air from the vehicle's exterior, often by way of a  blowing air over them, thereby transferring excess thermal energy from the engine to the air.

radiator fan: One or more sets of fan blades situated behind the which serve to move air from the exterior around the tubes of the, thereby dissipating heat from the engine block.

rear-view mirror:

rear-wheel drive (RWD): A system in which torque generated by the engine is delivered only to the two  at the rear end of the vehicle, as opposed to  and distinct from.

redline: The maximum rotational speed, in revolutions per minute (rpm), at which an or and its components are designed to operate without causing damage to the components themselves or to other parts of the engine assembly. The redline of a particular engine depends on various factors such as,, and the mass, composition, and balance of the engine components. The term is derived from the red-colored line or colored sector of a display which indicates the maximum allowable sustained engine speed. To operate a vehicle above its engine's redline. Straying above the redline usually does not mean instant engine failure, but may increase the chances of damaging the engine.

remote keyless system (RKS):

remote start:

roadworthy:

Describing a vehicle which is in suitable operating condition to be safely used on public roads, in which all parts are mechanically sound such that no part contravenes accepted standards for safe driving or transport of people or cargo or any other road transport regulation. The term often implies that the vehicle is.

rolling ratio:

S
scuttle:

semi-automatic transmission:

siping:

sludge:

soak time:

solenoid switch:

solid injection: See.

spare tire:

spark ignition: A system that uses a high-voltage electrical arc or "spark" to ignite a fuel/air mixture.

spark plug: An insulated plug that supports the electrodes between which the electrical arc or "spark" passes to initiate ignition of a engine.

speedometer: A gauge that measures and displays the instantaneous speed of a vehicle. Universal in modern automobiles and typically mounted on the behind the.

spoiler:

steering column:

steering wheel:

stick shift: See.

straight engine: See.

strangler: See.

street-legal:

stroke:

subframe:

sun visor:

supercharger:

suspension:

T
tachometer: An instrument which measures the rotational speed of a shaft or disk, as of an engine, and/or the analogue dial or digital device which displays this measured speed, usually in (RPM).

tailgate:

tailpipe:

The rearmost pipe of an, downstream of the rear, by which most or all of the vehicle's gases exit the system. The term is also sometimes used to refer to intermediate pipes. Large vehicles may have more than one tailpipe.

telematic control unit (TCU):

telematics: The range of electronic signals, displays, controls, and information provided to drivers so as to make driving easier and safer, whether inside the vehicle, on other vehicles, or on the roadside; or the interdisciplinary field that studies the implementation of these technologies. Examples include,, , digital , and any of the wide variety of features offered by systems, such as and.

throttle:

tie rod:

tire:

tire balance:

tire pressure:

tire rotation: The practice of periodically moving the and of an automobile from one position to another on the same vehicle in order to ensure that all of the vehicle's tires receive approximately the same amount of wear over time; i.e. that no particular tire wears out more quickly than any other. This is a consequence of the fact that a tire's lifespan is often strongly biased by its particular position on the vehicle (e.g. front or rear, driver's side or passenger side) because the masses supported by and the forces applied to different parts of the vehicle are often uneven; for example, in vehicles, the front axle typically supports a much greater load than the rear axle, meaning the tires on its wheels experience different forces that may cause their  to wear out faster than the tread on the rear tires.

torque:

traction:

traction control system (TCS):

trafficator:

transaxle:

transbrake:

transfer case:

transmission:

transmission control unit (TCU):

transmission fluid:

transmission tunnel:

transverse engine: An mounted inside a vehicle so that the axis of the is perpendicular to the direction of travel. This is common in  passenger vehicles. Contrast.

trim level:

trunk:

The primary storage or cargo compartment inside an automobile, especially a large interior space at the rear of the vehicle that is accessible from the exterior by one or more dedicated doors or hatches.

turbocharger:

turn signal:

two-stroke engine:

two-wheel drive (2WD): A system in which torque generated by the engine is delivered to only one pair of at a time, either the  or  wheels. Thus there are exactly two, while the other two wheels merely roll under the momentum imparted to them and do not create tractive force of their own. This is in contrast to (4WD), in which all four wheels receive power simultaneously. Some vehicles are only capable of two-wheel drive such that it is permanent, while in others it is a, with the vehicle capable of switching between two-wheel drive and four-wheel drive on-demand.

U
undercarriage: The wheels, axles, and system of a vehicle, particularly a commercial vehicle; more generally, all of the parts of an automobile accessible from the underside of the vehicle.

underdrive pulley:

understeer:

unsprung mass:

V
V engine:

valvetrain:

vehicle identification number (VIN):

W
wheel alignment:

wheel well: See.

wheelbase: The longitudinal distance between the front and rear wheel axes of a vehicle.

wheelfight: A rotary disturbance occurring in the that is produced by forces acting on the steered wheels.

whistle tip:

windshield:

The front window of an automobile, providing visibility in the forward direction of travel while protecting the occupants from the elements. Modern windshields are usually made of laminated safety glass, consisting of two curved sheets of glass with a plastic layer laminated between them, which is bonded to the window frame.

windshield wiper:

wing: British English for.

wing mirror:

wiring harness:

Y
Y pipe: A two-branch connecting the exhausts of a to form a single exhaust.