Automotive Technical Terms

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Throughout this site we use many technical terms, and given the breadth of readership our site enjoys, sometimes we are remiss and incorrectly assume everyone knows what we are referring to. For those that do not, here are some explanations of the technical terms use.


Used in conjunction with some coil spring rear axle set-ups. This type of location bracket stops the axle moving back and forward in relation to the body of the vehicle. The 'apex' of the "A" is fixed to the differential while the 'legs' of the "A" are fixed to the axle.


Upper and lower front suspension brackets; more generally termed wishbones. Used in conjunction with coil springs as a front suspension arrangement.


Front-most pillar in vehicle body construction that joins the roof to the lower portion of the body. Successive pillars are called B, C and (with wagons) D.

Accelerator Pump:

Attached to the carburetor body, it performs the specific function of negating the lean-out effect caused by sudden large throttle openings. It is activated directly off the throttle cable (or linkage) via a diaphragm arrangement and nozzle. Sudden throttle openings activate the diaphragm which forces petrol through the nozzle into the carburetor throat. On slow throttle openings, there is a bleed-by arrangement that allows the fuel to return to the pump bowl rahter than being forced through the nozzle.


There are two types, oil and fuel. Oil additives make up about 15% of oil volume and are used to inhibit oil oxidisation (the main reason for oil breakdown) and to clean carbon deposits (detergent additives). The main fuel additive is teteathyl lead which is used for its anti-knock properties; its addition allows octane levels to be dropped without fear of creating mechanically dangerous pre-ignition or pinging.

Advance and Retard:

This refers to the change in ignition timing that is made through both mechanical and vacuum systems to allow for different combustion situations for different rpm and smaller or larger throttle openings. The mechanical system advances the ignition as rpm increases to allow for the decreased time for combustion.


The study of physical forces at work when a body passes through the air. In the automobile world, the term aerodynamic drag is used to describe the resistance that the air exerts on a car moving at speed. By changing the body shape of a car to reduce dynamic drag, the energy output of the engine can be better utilized either in the form of reduced fuel consumption or improved performance. The French auto manufacturer Citroën pioneered the development of aerodynamic passenger cars with the DS19 in 1955, and have remained leaders in this field.


Also termed “wing” or “wings”, these devices were first fitted to race cars to to increase down-force and thus traction at high speed. The greatest benefit, apart from keeping the car firmly on the road, is to allow higher cornering speed.

Air Dam:

An aerodynamic aid placed across the lower nose of the car to prevent the energy consuming and dynamically un-stabilising effect of air being forced under the car.


A device fitted to the engine to convert mechanical rotational energy into electrical energy. This electrical energy is stored in the battery and used to operate the various electrical functions of the car.


An instrument for measuring electrical current and hence the electrical output of the alternator

Anti-Dive Geometry:

A particular type of suspension arrangement that minimizes nose dive and tail-end lift during heavy braking. It produces a more comfortable ride as well as providing higher levels of traction.

Anti-roll Bar:

A suspension aid that increases resistance to body roll without giving a stiffer, less comfortable ride. The centre of the bar is attached to the underside of the body, the ends of the bar are bent through right angles and attached to the suspension control arms.

Aspect Ratio:

Refers to the height of the tire expressed as a percentage of the cross-section profile. Hence a 70% aspect ratio refers to a tire that is 70% as high as it is wide.
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