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.

Ball Joint:

Common name for ball-and-socket joints used on steering arm ends and suspension components where two-directional movement is required between joined components.

Beam Axle:

Used widely before the advent of independent front suspension, beam axles became more prevalent as part of the rear suspension set-up of front-wheel-drive cars through the 1970’s and 1980’s. They are a one-piece solid transverse members usually suspended on coil springs, but in the case of heavy commercial vehicles they are used as a front suspension component in conjunction with leaf springs.


European term used to describe sedan or saloon body styles, before becoming used by GMH in Australia to define their mid-luxury Commodore variant. Other European terms describing sedan style include Berline and Berlinetta.

Bias Belted:

A tire construction technique developed in the US that consists of a mixture of cross-ply and radial-ply construction. It is aimed at producing a superior ride comfort level than that found with a radial ply tire without sacrificing any road-holding capabilities. The bias-belted tire fell from favor during the late 1970’s.


Hand preparation and assembly of an engine or other mechanical components to ensure correct tolerances are achieved and thus optimum performance obtained. Can include x-ray type techniques used to determine minor imperfections not detectable to the human eye. Commonly includes; Block - Align hone main saddles, parallel boring and honing with deck plates, equal-distance decking; Pistons - Checked for size and dome height and then pin fitted; pistons are notched where necessary for valve clearances, Crankshaft - Magnafluxed, indexed, machined; oil holes radiused, journals micropolished. The compression ratio is calculated for maximum performance; Balancing - The entire rotary assembly is precision electronically balanced.

Big End:

The connecting point of the connecting rod to the crankshaft.


Colloquial term to describe a super-charger or turbo-charger.


Originally a French term, but now used widely by all manufacturers to describe soft-top or convertible style automobiles.


Driven off the crankshaft, the camshaft consists of a series of machined eccentric lobes that open and close the valves, thus controlling gas flow in and out of the cylinder head.

Compression Ratio:

A calculated ratio that relates the uncompressed volume of the cylinder with the piston at bottom dead-centre to the compressed volume of the cylinder with the piston at top dead-centre. Hence a 9:1 compression ratio means that the air-fuel mixture is compressed to one-ninth of its original volume before being ignited. The compression ratio bears little relationship to the actual effective pressure created in the cylinder.


Short for “connecting-rod”, it joins the piston assembly to the crankshaft and is an essential component in power transmission.

de Dion:

Refers to French auto designer de Dion and his independent rear suspension that utilizes a connecting tube.


Also called “pinging”, refers to the mechanically dangerous situation where combustion is uncontrolled and not a function of ignition. Generally a result of an incorrect air-fuel mixture or too high a compression ratio for the octane level of the fuel.


Gear assembly that transmits power from the drive shaft to the wheels.  The name is derived from the provision that allows one wheel to turn at a different rate to the other wheel.


Swept volume of a cylinder or a group of cylinders comprising an engine. Formerly expressed in cubic inches (cu. in), it is now measured in cubic centimeters (cc) or liters (L).


Shaft-driven mechanical device that controls a low-tension ignition circuit by making and breaking contact.


Double overhead camshafts. Originally only found in high performance engines, they have become common-place on all modern engine designs.

Drive Line:

Transmission shaft that takes power from the gearbox to the differential. Usually incorporates two universal joints to allow for suspension movement.
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