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.

Shock Absorber:

Alternatively 'damper', generally a hydraulic device that minimises unnecessary road spring oscillations.


An electrical device that consists of a sliding iron bar within an electrical coil. Used to transfer electrical energy into mechanical motion. Main automotive application is in starter motors.

Spark Plugs:

Screwed into the combustion chamber and used to ignite the compressed air-fuel mixture.

Steering Ratio:

Steering systems are geared down, usually in the ratio 3:1 to 5:1 to reduce the steering effort. The ratio indicates how many times the wheel is turned to move the road wheels from one lock to the other, and so a ratio of 3:1 would require three complete rotations of the steering wheel to complete a lock to lock transition.


The piston stroke from top dead centre to bottom dead centre.

Swing Axle:

Independent rear suspension favored by the European manufacturers through the 1950's to late 1960's, typically found in the Volkswagen Beetle, some Mercedes models and rear-wheel drive Renault's. It consists of independently sprung shafts that are attached directly to the gearbox.


A function of a gearbox that allows gears to engage without noise.


An instrument that measures engine speed in revolutions per minute.


Part of a rocker assembly that actuates both inlet and exhaust valves and has a facility for valve clearance adjustment.

Torque Tube:

A tube that fully encloses a propeller or drive shaft that helps relieve the rear springs of driving and braking forces. A superior but older design, most commonly found on the Peugeot 404.

Torsion Bar:

A type of spring commonly used in automotive suspension that consists of a high tensile steel bar that is fixed solidly at one end while the other end is attached to the suspension arm or wishbone. The springing effect is created by twisting the bar around its own axis.


The lateral distance between the wheels of a vehicle. Most cars have different front and rear tracks.

Trailing Arms:

A type of indepoendent suspension found on the rear of many front-wheel-drive vehicles. Consists of a single arm per wheel that moves parallel to the longitudinal axis of the car.


A mechanical component that consists of the gearbox, clutch, differential and final drive gears combined in one unit. Originally found in the VW Beetle and rear-wheel-drive Renault's, then in the Porsche 924 and Alfa Romeo Alfetta's.

Transistorised Ignition:

An ignition system that utilises magnetic induction or other electronic means to make and break the low-tension ignition circuit, it has today replaced the use of control breaker points.

Tuned Length:

Refers to an exhaust or inlet system that has a specific length designed to optimise performance in a specific rev range, usually at higher revs.

Twin Choke:

A type of carburetor that has two chokes or throats instead of the usual single throat. Several types are found including those whose throats open simultaneously and progressive types where the second throat opens after the first throat is approximately two-thirds open.
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