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Motorcycle Glossary of Terms


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Rack-and-pinion - A pinion gear on the end of a shaft that mates with a rack. Sometimes used in clutch operating systems.

Radial play - Up and down movement about a shaft.

Radial ply tyres - Tyre piles fun accross the tyre (from bead to bead) and around the circumference of the tyre. Less resistent to tread distortion than other tyre typres.

Radiator - A liquid-to-air heat transfer device designed to reduce the temperature of the coolant in a liquid-cooled engine.

Rake - A feature of steering geometry - the angle of the steering head in relation to the vertical.

Rat bike - A motorcycle not necessarily kept in pristine condition, often painted matt black. Minimal maintenance and mismatched parts often used.

Rear sets - Racing-style footpegs, an aftermarket product designed for racing. Allows the rider multiple riding positions as they are adjustable.

Rebore - Providing a new working surface to the cylinder bore by boring out the old surface. Necessitates the use of oversize piston and rings.

Rebound damping - A means of controling the oscillation of a suspension unit spring after it has been compressed. Resists the spring's natural tendency to bounce back after being compressed.

Rectifier - Device for converting the ac output of an alernator into dc for battery charging.

Red line - The maximum number of revolutions per minute an engine can run before damage occurs. Typically indicated on the rev counter.

Reed valve - An induction system commonly used on two-stroke engines.

Regulator - Device for mainitaining the charging voltage from the generator or alternator within a specified range.

Relay - An electrical device used to switch heavy current on and off by using a low current auxillary circuit.

Resistance - Measured in ohms. An electrical component's ability to pass electrical current.

Rev counter - displays the amount of revs per minute (rpm).

Road rash - a term used to describe the injury to a person's skin when a rider falls or slides along the road, hence the importance of using adequate protection when riding.

Rotary - Ccommon term for a Wankel engined motorcycle.

Rotary valve - A valve driven from the camshaft for inlet or exhaust and usually a disc or cylinder shape. For either 2 or 4-stroke engines.

rpm - Revolutions per minute

Rubber - tyres.