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.


Alternatively 'knock.' Engine noise caused by pre-ignition (see Detonation).


Passage in cylinder head for gas flow either from or to a combustion chamber. Flow is controlled by the movement of the valves.

Power-to-Weight Ratio:

Ratio of a vehicle's power to its curb weight. Generally expressed as kilowatts per kilogram.

Power Steering:

A steering system where engine manifold vacuum other assistance (more increasingly via electrical motor) is applied to the steering to decrease steering effort.


A long thin metal rod, one end of which contacts the camshaft through follower “buckets”; the other end operates overhead valves through rocker arms.

Quartz Iodine Halogen:

Special type of headlight filament that uses a quartz element in either iodine or halogen atmosphere and produces a light at greater intensity than incandescent globe.

Rack-and-Pinion Steering:

A simple but effective and precise steering arrangement that consists of a small cylindrical pinion gear that engages a flat tooth rack.

Radial Ply:

A type of tire construction where the plies are layered radially across the tire Generally gives superior road holding and ride-comfort levels.

Rear Brake Proportioning Valve:

A valve that proportions brake pressure between the front and rear wheels, preventing rear wheel lock-up.

Recirculating Ball Steering:

A type of steering mechanism typically found on earlier Japanese passenger cars. Favored by the Japanese because it greatly reduced the steering effort required, the trade-off being that it also provided vague steering response.


Pivoted laver that actuates inlet and exhaust valves by transmitting the reciprocating motion of a push-rod or the eccentric motion of a camshaft.


Alternatively "Revs", refers to engine speed in revolutions per minute.

Running Gear:

Mechaniocal components attached to frame and body shell. Includes suspension, axles, wheels and brakes.
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