Rack and Pinion Steering
A steering gear in which a pinion on the end of the steering shaft merges with a rack of gear teeth on the major cross member of the steering linkage. When the steering wheel is turned, the pinion gear turns, moving the rack to the left or right, thus steering the wheels.

Residual
A conservative projection of the market value of a vehicle at the end of a lease. Residual values are provided by major auto manufacturers or independent companies that specialize in auto valuation.
A higher residual value will lower the monthly payment. However, the vehicle must be resalable at the residual amount or the lessor will lose money. Conversely, adjusting the residual too low will increase the monthly payment and may make the lease payment unattractive. Adjustments to residual may be made for excess mileage or wear and tear.

Resonator
A small auxiliary muffler that assists the main muffler in reducing exhaust noise.

Ring-and-Pinion Gear
Any gear set consisting of a small gear (the pinion gear) which turns a large-diameter annular gear (the ring gear). Used in rear-drive differentials (rear ends) to transfer power from the driveshaft to the axle and wheels.

Rolling Radius
Tire-rolling radius is the distance from the center of the wheel to the road. Static radium applies when the vehicle is standing still. Dynamic rolling-radius described wheels in motion. The latter is used to measure tire revolutions per mile and is usually slightly higher than static radius.

Rolling Resistance
This is motion resisting force that is present from the instant the wheels begin to turn. On normal road surfaces, rolling resistance decreases with increased tire pressure and increases with vehicle weight. Rolling resistance can also be affected by tire construction and tread design.

RPM
Rotations per minute.

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