Scrub radius: The distance from the point where the steering axis meets the ground to the longitudinal line passing through the middle of the contact patch of the tyre on the ground.

Saloon: A car with two or four doors, a single compartment with two rows of seats, one at the front and the other at the rear.

Roll angle: The angle through which vehicle body turns about its longitudinal axis while negotiating a corner.

Roll: Turning of a vehicle about its longitudinal axis.

Road isolation: The ability of a vehicle to absorb or isolate road shocks sum the passenger compartment.

Road holding: The degree to which a vehicle maintains contact with the road surface in various types of directional changes, e.g., dip, squat, cornering, etc., and in a straight-line motion.

Ride: Qualitative ability of a vehicle to provide a smooth, comfortable drive on a bumpy road.

Reversible wheel: A wheel whose disc can be mounted on either face to provide 'inset' or 'outset', thus decreasing or increasing the wheel track.

Regenerative braking: Form of braking in electronic or electric hybrid vehicles in which energy of road wheels of moving vehicle is used during braking, to run the electric traction motors as generators for charging battery pack.

Rebound: Wheel motion when it moves down relative to the body.

Ratchet screw driver: A screw driver with a ratchet mechanism.

Ratchet: A feature of a special wrench which allows you to turn the handle in one direction to tighten a nut or bolt, but on turning in the opposite direction, does nothing but position the handle back where you started to continue tightening.

Radius rod or Thrust member: The member connecting the axle casing and the chassis frame in the longitudinal direction, which transmits the driving thrust from the axle casing to the chassis frame and body of the vehicle. This is also called thrust member.

Radial tyre: A tyre which has body cords running at right angles to the tyre centre line. Two or more belts are used to give tread strength. Such a tyre can be identified by its characteristic sidewall budge, when installed on the vehicle.

Propeller shaft: This is the shaft which transmits the drive from the transmission (gear box) to the bevel pinion or worm of final drive in front engine, rear drive vehicles.