Expand your four-wheelin’ knowledge with our glossary of terms. The more you know, the more capable you’ll be, whether you’re off the road or under the hood.
A-Arm: An A-arm is a three-sided component that goes into an independent suspension. You might hear this referred to as the upper or lower control arm. The two ends of the “A” pivot on the chassis, while the third end connects to the spindle.
ABS: ABS stands for anti-locking braking system. Anti-lock brakes are designed to avert skidding when you hit the brakes hard; electronics are used to equalize and manage the speed of the wheels. Two-channel ABS manage the rear wheels only. A four-channel ABS manages all four wheels.
Ackerman Angle: The turning angle of an inside wheel is different than the turning angle of the outside wheel, because the inside wheel travels a shorter path. This difference, which is an engineered value, is called the Ackerman angle, also known as toe-out turns.
Add-a-Leaf: This term refers to an affordable technique for lifting a vehicle, which involves inserting an extra leaf to the leaf spring pack. Add-a-leaf achieves the lift, but degrades ride quality.
Aftermarket: Aftermarket describes automotive parts that are not produced by an original equipment manufacturer (OEM).
Amp Draw: Amp draw is the amount of ampere-hours consumed by a piece of electrical equipment during operation. An ampere-hour is a measure of the energy a battery can hold and supply at a specific voltage.
Approach Angle: Approach angle refers to the steepest angle a vehicle can climb before the body, front-mounted equipment, or chassis makes contact with the ground.
Arch: Arch is a synonym for camber. Outside the ‘wheeling world, a camber is a slight curve. The automotive form of the word refers to either the curve in a leaf spring, or the tilt (inward or outward) in the tops of the front tires. If you are looking at a vehicle from the front and the tires are tilted out, this is positive camber. If they’re tilted in, that’s negative camber.
Articulation: Articulation describes the flexibility of an off-road vehicle’s suspension. In other words, articulation is a suspension’s capacity to combine compression and droop on one axle. Ideally, the body remains generally level while the axles work at angles to navigate uneven ground.
Aspect Ratio: Aspect ratio is a tire's height divided by its width, expressed as a percentage. The ratio characterizes the profile of the tire.
Axle Wrap: Axle wrap describes when an axle turns in the opposite direction of the circular torque generated through acceleration. Tension builds in the spring, but it will eventually snap back harshly. This happens more often when towing, and can be destructive to drive shafts and u-joints.
Backspacing: Backspacing is the distance between the inside edge of the rim and the mounting flange.
Bead: On a tire, the bead is the edge of the tire that meets the rim. The belts of the tire attach to high-tensile steel wires that make up the bead. This construction allows the tire to grip tightly onto the wheel.
Bead Seat: The bead seat is the part of the bead where the seal is created between the tire and the rim.
Bead Filler: Bead filler is a wedge of hard rubber compound, placed in the lower sidewall of a tire. Its purpose is to reinforce the portion of the tire near the bead.
Beadlock: A beadlock is a mechanism that maintains the seal between the bead and the rim when the tire pressure is too low. Beadlocks are built into rims.
Beater: Beater is a slang term for a vehicle that’s physically beat up. Often, a “beater” will look worn on the outside, but still run reliably.
Beef: Beef is a slang term for strength.
Binder: Binder is a shortened version of “Combinder,” which describes autos produced by International Harvester Company.
Birfield: A Birfield is a six-ball, constant velocity (CV) joint. These joints are favored by Japanese companies including Toyota. The design dates back to Hans Rzeppa in the 1920s and, later, England’s Birfield Ltd. In the 1960s, the Toyota Land Cruiser brought the Birfield joint into the mainstream. The tooling involved in the production of these joints was notoriously pricey and intricate. Many of these joints on the Land Cruiser were marked with a “Birfield” stamp.
Blip: Blip refers to a swift jab of the throttle.
Bogger: Bogger is a term for a very aggressive tire designed for mud driving. The word can also refer to an off-road vehicle built for mud driving. (See: Super Swamper Tires Bogger)
Bolt clips: Bolt clips maintain the top alignment of spring leaves. Cinch clamps can perform the same function, although they will restrict movement.
Bottom: A vehicle “bottoms” or “bottoms out” when the suspension compresses to the point of hitting the rubber bumpers (bump stops) on the chassis.
Boxing: Boxing is a modification that strengthens the chassis. The open areas of a “C” or “U” section are closed off with extra material.
Built: Built is an adjective that’s used to describe any vehicle that has many upgrades. Built is a short synonym of built-up.
Bump Steer: Bump steer refers to steering changes that occur when a vehicle hits a bump in the road. When the vehicle makes contact with the bump, the steering wheel will shift and the vehicle’s direction of motion will change. At low speeds, suspension movement can cause bump steer. This is relatively common in 4x4 vehicles. Bump steer can be unsafe if it happens when the vehicle is traveling at high speeds.
Center Axle Disconnect or CAD: Center axle disconnect is a system that uses a splined, sliding collar to disconnect the longer front axle shaft from the differential. On open differentials, this keeps the drive shaft from turning in two-wheel drive. CAD, an alternative to front-locking hubs, permits the differential side and spider gears in the differential to turn. Install a limited slip or locker and the left axle will propel the ring and pinion and drive shaft, which can create shuddering at higher speeds.
Camber: Camber is a synonym for arch. Outside the ‘wheeling world, a camber is a slight curve. The automotive form of the word refers to either the curve in a leaf spring, or the tilt (inward or outward) in the tops of the front tires. If you are looking at a vehicle from the front and the tires are tilted out, this is positive camber. If they’re tilted in, that’s negative camber.
Camber Roll: Camber roll represents how much the camber increases when you steer a vehicle hard to the left or right. Some camber roll is good because it supports traction. Too much camber roll can cause wear on the tires.
Cardan Joint: This is the original name for the universal joint or U joint. Other synonyms for Cardan joint are universal coupling and Hardy-Spicer joint. The joint is named after Jerome Cardan, an Italian mathematician of the 16th century.
Caster: Caster refers to tilting of the steering axis. When the top pivot tilts towards the front of the truck, this is referred to as negative caster. Positive caster tilts the top pivot towards the back of the truck.
Center of Gravity: Center of gravity is the spot on a vehicle where all planes are balanced. For many off-road vehicles, the center of gravity is a foot or two off the ground and slightly forward from the center. A vehicle’s center of gravity influences how easily that vehicle will roll over. A high center of gravity means the vehicle is less resistant to tipping.
Chunk: When a tire “chunks,” it loses tiny pieces of tread. This often results from high temperatures and friction, but chunking can also occur when the tire is driven on rocky terrain or when the tire has been siped.
Compression: Compression is how high the suspension moves up above its static position. Contact Patch: On a tire, the contact patch is the surface that meets the pavement or terrain and creates traction. Tire size and tire pressure influence the size and shape of the contact patch.
Crossover SUV: A crossover SUV is an all-wheel-drive car or minivan. This can also include cars that have been converted to all-wheel-drive.
Crossover Steering: In a crossover steering system, the drag link and tie rod are individually connected to the knuckle on the passenger side. At the wheel ends, the steering knuckles are brought together with the tie rod.
Cross-Axled: A vehicle is cross-axled when the front axle and rear axles are articulated in different directions. If you are looking at a cross-axled vehicle from the front, the axles form a low x shape.
Crawl Ratio: Crawl ratio, also called final drive ratio, is a vehicle’s lowest possible gear ratio.
CV-Joint: CV stands for constant velocity. CV joints are used on drive shafts and steering axles to transmit power smoothly without chatter. There are several types of CV joints, including the six-ball types (Rzeppa and Birfield), the four-ball Bendix, and the Herrington, which is comprised of two U joints.
Dead-Man: A dead-man is an anchor point in a winch operation. Trees or other vehicles are common anchor points, but the dead-man can be anything strong enough to remain stationary as force is applied against it.
Death Wobble: Death wobble is an exaggerated slang term for extreme steering vibration.
Deep Gearing: Deep gearing is a synonym for low gearing.
Deflection: Deflection is the compression of a tire when it’s carrying a load, versus carrying no load. More specifically, this is the change in a tire’s radius between when it has no load and when it has a full load. The term can also be used more generally to mean the contraction of a spring.
Departure Angle: Departure angle refers to the steepest angle a vehicle can descend before the body or chassis makes contact with the ground.
Directional Stability: A vehicle or tire has directional stability when it can travel straight, despite pits or other abnormalities in the road’s surface.
Drag Link: A drag link is the steering rod that links the steering box Pitman arm and the tie rod.
Droop: Droop is synonymous with jounce. Both words refer to suspension compression below the truck’s typical ride height.
Drop Pitman Arm: On a lifted vehicle, a drop Pitman arm can be used in lieu of a Pitman arm to fix steering issues (such as bump steer) resulting from the lift.
Duty Cycle: Duty cycle represents how long a piece of equipment can run before it becomes damaged. The cycle is time in operation relative to time the equipment is shut off.
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