radius arms Brackets used by Ford that locate the front axlehousing on coil-spring suspensions. Dodge and Jeep use similar brackets. Syn. trailing or control arms.
rack-and-pinion A steering system that uses a pinion gear at the end of the steering shaft to engage a horizontal-toothed bar, the rack, which is attached to the tie rods and the steering knuckles.
rake When the frontend of a truck sits lower than the rear.
ramp breakover angle The angle formed by lines drawn from the front and rear tires' contact patches and the midpoint of the wheelbase on the chassis; the greater the angle, the less likelihood of high-centering.
Rat Chevy big-block V-8 engines, normally offered in 396ci, 402ci, 427ci, and 454ci sizes. Named because it was a large companion to Chevrolet's small-block Mouse V-8.
rebound After a suspension spring is compressed by a bump, the spring naturally tries to return to its previous length, extending the suspension upward toward its original ride height.
recirculating ball steering Steering assembly that uses a worm gear on the end of the steering shaft to turn a sector gear that is within the steering box and attached to the pitman arm. Ball bearings are used between the worm and sector gears for smooth operation.
redline Absolute maximum engine speed, expressed in rpm, at which an engine can/should be operated; indicated by a red line on the tachometer. Syn. rev limit.
repro Aftermarket reproduction parts, manufactured to appear, fit, and function as originals. Not the same as OE or N.O.S., which are both factory-issued parts.
restify To build a truck that is basically restored but has been updated with modern convenience and performance enhancements.
retrofit Installing new parts or systems on an older truck for the purpose of upgrading, such as retrofitting a modern fuel-injection system in place of the original carburetor.
rev limiter An adjustable electronic device that restricts engine rpm to a predetermined limit so engine damage does not occur.
reverse-rotation Refers to an axle design where the pinion is positioned above the axle centerline.
ring-and-pinion Gearset that drives the wheels; the pinion is a gear attached to the rear of the driveshaft, and the ring gear is part of the differential that turns the axles.
rock magnet A low-hanging component of a 4x4, such as a ladder bar, that seems to catch on every obstacle.
rock massaging Body damage caused by rocks and other obstacles on the trail.
rocker arm Pivoting valvetrain levers. One end of an engine's rocker arms are moved by the pushrods/lifters and the opposite end's open intake or exhaust valves.
rocker panel The sheetmetal section of a truck's body located below the doors and between the front and rear wheel openings.
Roots supercharger Positive-displacement, beltdriven supercharger; originally designed in 1859 by Francis Roots for use as a water pump.
RTI Ramp travel index, a measurement of suspension flexibility and articulation that's calculated by dividing the distance the hub's centerline travels up a (usually 20-degree) ramp by the vehicle's wheelbase in inches, multiplied by 1,000.
sanitary Well designed, engineered, and constructed; cleanly built; superior mechanical workmanship. Syn. sano.
semi-floater An axle assembly that carries the weight of the vehicle on the axleshafts. These are typically weaker than full-floaters.
serpentine belt Engine accessory drivebelt that is long and follows a snaking path while driving the alternator, water pump, A/C unit, and power-steering pulleys.
shackle Connector between the rear of a leaf-spring pack and the frame; allows the spring to lengthen as the suspension is compressed.
shift kit Package of high-performance components for an automatic transmission that firms the shifts, alters the shift points, and improves overall performance.
shiny-side down When a truck rolls over. Syn. rubber-side up.
short-block An engine block that has a complete bottom end, including the crankshaft, rods, pistons, and camshaft, but without the cylinder heads, intake and exhaust manifolds, water pump, and other accessories.
sidehill A portion of a trail that leads across a steep hill instead of up or down. See off-camber.
single-plane manifold Intake manifold with a single plenum feeding all of the engine's intake runners.
skin Body sheetmetal.
skins Tires.
slickrock A type of sandstone dominant in Moab, Utah. Slickrock actually isn't slick and provides excellent traction.
slushbox An automatic transmission. Syn. juicebox.
small-block A V-8 engine typically having 400 or less cubic inches of displacement.
snatch-block A pulley device used in assisting with getting unstuck; it doubles as a winch cable's pulling power.
snatch strap A thick nylon strap used to pull out stuck vehicles. Syn. tow strap, yank strap.
spool out To pull the winch cable off the drum after releasing the brake.
spotter A codriver who helps guide the driver over obstacles, often using hand signals.
spring rate The force required to deflect a spring 1 inch, expressed in pounds per inch of spring compression or deflection. The higher the per-inch spring rate, the stiffer the spring.
spun bearing A bearing that is either worn or frozen and has rotated in its retainer. In an engine, this causes the bearing to block off its oil passage and results in major damage.
stair-step An obstacle that contains one or more ledges that must be climbed in succession. Stair steps are common on trails that follow washes or creek beds.
stand on it Full-throttle acceleration.
swamped To drown the engine; to drown the entire truck.
synthetic oil Manmade lubricants; they generally have a greater capacity to lubricate and resist heat than standard mineral oil.