- R -

Rod-end Bearing

The spherical bearing found at the end of a suspension arm or rod.

Rod-length Ratio

The center-to-center length of a connecting rod divided by the piston stroke.

Rod-to-stroke Ratio

A term used for rod-length ratio.

Roll

1. To turn over and over. 2. To tip or sway side-to-side. 3. The motion of a vehicle body toward the outside of a turn when cornering or changing directions suddenly.

Roll Axis

The longitudinal axis of a vehicle defined by an imaginary line running through the front and rear roll centers.

Roll Bar

A tubular bar behind the cockpit of a race car to protect the driver in case of a rollover.

Roll Cage

A tubular, cage-like structure surrounding the cockpit of a race car to protect the driver in case of a rollover and to add strength to the overall structure of the vehicle.

Roll Centers

The points at the front and rear about which the vehicle's spring mass will roll.

Roll Out

The distance a race car travels in a drag-racing event at the beginning of a run before the front tires clear the stage beam and start the clock.

Roll Steer

The direction and amount that the rear axle may cause the vehicle to steer as it moves through its travel when the body rolls during cornering requiring the driver to oversteer or understeer to compensate for the problem.

Roll Stiffness

The resistance, measured in pounds per inch of spring travel, of a suspension system to the rolling of the vehicle's mass.

Roller

1. A race car offered for sale without an engine. 2. A cylindrical locking element of a one-way roller clutch. 3. A Rolls-Royce.

Roller Bearing

A bearing using rollers within an outer race or ring.

Roller Cam

A camshaft having a small roller at the base of each lifter.

Roller Chain

A timing chain having rollers that engage the gear sprockets.

Roller Clutch

A one-way clutch containing a number of rollers that operate by wedging on a ramp between an inner and outer race to lock up (drive) when the outer race is turned in one direction, and to slip (overrun) when it is turned in the opposite direction.

Roller Lifter

A valve lifter, used in some high-performance engines, featuring a roller which contacts the camshaft to reduce friction.

Rolling Diameter

A term used for tire rolling diameter.

Rolling Radius

The distance between the center of the wheel and the contact points of the tire on the ground under the weight of a vehicle.

Rolling Resistance

The pounds of force required to overcome the resistance of a tire to rotate.