Off-Road Terms Glossary

Stands for anti-lock braking system. They are designed to prevent skidding when you hit the brakes hard, but not locking up, but rather a rapid lock release action allows some steering whilst braking.

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.

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 describes automotive parts that are not produced by an original equipment manufacturer (OEM).

The measure of force exerted by the air inside a tire, typically measured in pounds per square inch (PSI), or kilopascals (kPa).

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 refers to the steepest angle a vehicle can climb before the body, front-mounted equipment, or chassis makes contact with the ground.

Aspect ratio is a tire's height divided by its width, expressed as a percentage. The ratio characterizes the profile of the tire.

An Axle Shaft is the part of an axle assembly that is turned by the side gear of the differential and transfers the power either directly to the wheel or to the wheel hub that the wheel is bolted to, depending on the style of axle.

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.

Also known as rearspacing, this is the distance from the mounting pad to the back edge of the rim. Not to be confused with wheel offset.

The even distribution of weight on a mounted wheel and tire.

Ball joints connect the steering knuckle to the axle housing, or arms, and hold it in position while allowing the steering motion.

The part of the tire in contact with the wheel flange. It is made of high tensile steel wires shaped to fit the rim and hold the tire on the wheel. The steel wires are wrapped in woven fabric and held in place by the plies.

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.

The bead seat is the part of the bead where the seal is created between the tire and the rim.

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.

A Bearing provides a low friction surface that allows two parts to move on a single axis.

Beef is a slang term for strength.

A tire constructed with plies laid out in alternating directions in angles about 30-40 degrees to the center line of the tire. The plies form a criss-cross pattern that is typically suited more towards off road driving.

Blip refers to a swift jab of the throttle.

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)

The number of lug holes on the diameter of the imaginary circle that each lug hole is centered upon.

Bolt clips maintain the top alignment of spring leaves. Cinch clamps can perform the same function, although they will restrict movement.

The arrangement of bolt holes on a wheel. Some wheels have more than one bolt pattern on the same wheel to accommodate multiple fitments.

Referred to as a brake caliper, it applies pressure on a spinning disc (rotor) to slow a vehicle.

Also referred to as Vernier Calipers. A tool used to take precise measurements in thousandths of an inch.

The angle of the centerline of a tire and wheel relative to completely vertical.

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.

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.

Sometimes referred to as a Differential Case or Ring Gear Carrier. This unit transfers the motion from the ring gear to the axle shafts.

These are the bearings that ring gear carriers ride on. May also refer to the driveshaft support bearing used in multiple-piece driveshafts.

Wheels that are made from liquid metal poured into a mold. Low pressure casting involves pouring the metal into a mold, while counter-pressure casting involves sucking the metal into a mold like a vacuum. Counter-pressure casting reduces impurities to make the wheel much stronger than a low pressure cast rim.

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 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.

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.

The cross shaft is a hardened pin that transfers a load from the carrier case to the spider gear assembly.

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.

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.

A crossover SUV is an all-wheel-drive car or minivan. This can also include cars that have been converted to all-wheel-drive.

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.

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 is an exaggerated slang term for extreme steering vibration.

Deep gearing is a synonym for low gearing.

Departure angle refers to the steepest angle a vehicle can descend before the body or chassis makes contact with the ground.

An instrument used for tracking precision measurements down to 1 thousandth of an inch.

The differential is a device that usually consists of gears. These gears allow each of the driving wheels to rotate at different speeds, while supplying equal power to each of them.

DOT is an acronym that stands for Department of Transportation. The 10-digit code after the DOT designation provides information such as the week and year the tire was produced, plus the manufacturer, plant, tire line, and size.

Drag is a load or resistance keeping something from turning freely.

A drag link is the steering rod that links the steering box Pitman arm and the tie rod.

The Drive side of the gear refers to the convex or crowned side of the ring gear. This side of the gear is the side of the tooth that the pinion gear pushes off to turn the ring gear when accelerating forward. This holds true in all but standard rotation front differentials where it is reversed.

The drop out refers to a particular type of axle that has a separate gear case assembly that can be removed from the housing (picture A). This is opposed to an axle that has the gears installed into the physical axle housing (picture B).

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 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.

The word Flange is used to describe many different items in a vehicle, but generally it refers to a flat mounting surface to couple two pieces together.

A Gasket is a type of seal between two mating surfaces preventing leaks.

The heal is the part of the ring gear tooth that the pinion contacts first. This is the very outside of the gear tooth.

When the drive shaft does not come into the middle or center of the diff housing, but rather high up and offset.

This term refers to the main body of the axle assembly.

A situation wherein the center bore of the wheel is made to match up with the diameter of the automobile hubs; the wheel is then balanced by the center hold rather than the lug holes.

I.F.S. is short for Independent Front Suspension. This type of suspension allows each wheel to move independently of each other over an obstacle.

Short for Independent Rear Suspension. This type of suspension allows each wheel to move independently of each other over an obstacle.

Inner axle refers to the innermost axle shaft of a two-piece axle assembly.

King pin is a type of steering knuckle pivot. This system shares the same job as a typical ball joint but is believed to be stronger than the ball joint. This system has basically been phased out by ball joints.

The steering knuckle is the main component that allows a solid axle to perform its steering function. The knuckle is usually retained to the housing by the ball joints or king pins.

The Limited Slip is basically a preloaded open differential. Also known as a Posi, these units usually use a set of clutch springs to preload the spider gear set between 150-450 ft. lbs. This preload provides a breakaway setting. This breakaway is the f

Most lockers use a type of ratcheting devise to lock the axles together when power is applied to the unit and allow one wheel to disengage while turning. These units are suited for the more aggressive wheeler as these units do have some drivability concerns. Although minor, these units usually clunk and bang but are better suited for the street than a spool. These units will turn both tires even if one is off the ground.

The locking Hub is a device that allows the wheel bearing hub to be disengaged from the axle shaft. This function is used in part time 4 wheel drive vehicles to reduce the additional drag of the drivetrain when the 4 wheel drive is not needed.

Standing for long wheel base, these usually include most normal and full size pickups and SUVs. In LWB SUVs, they usually have 5 doors, but there are also some LWB SUVs with a panelvan type configuration with only 3 doors. These wheelbases are usually around 110 inches or longer.

Standing for mid wheel base, these are usually longer than short wheel base vehicles, but shorter than long wheel base vehicles. The often combine the best benefits out of both configurations, making for a greatly maneuverable off-roader, with great approach, break-over and departure angles, and still offers great on-road and high speed stability.

The diameter of an inflated tire without any load.

Pattern refers to contact pattern between the gears. This contact pattern is used to see how the pinion gear is contacting the ring gear. By reading this print, you can determine if different shims are required to set up the proper gear mesh.

Pinion angle refers to the angle that the axle yoke is at compared to the drive shaft and the transfer case or transmission.

The pinion gear is the drive gear that turns the ring gear

Pinion Pre Load is the amount of drag that is required to turn the pinion shaft. Drag is a load or resistance keeping something from turning freely

Pinion Yoke is a part that connects the pinion shaft to the drive shaft.

Changing the original stock tire size of your vehicle in order to enhance vehicle performance by allowing for fitment of larger wheels and tires. It is recommended that you keep the overall tire diameter within 3% of OEM tire size to prevent problems with transmission, gas mileage, and braking.

Posi is another name for a Limited Slip. The Limited Slip is basically a preloaded open differential. These units usually use a set of clutch springs to preload the spider gear set between 150-450 ft. lbs. This preload provides a breakaway setting. This breakaway is the force required to allow the axles to differentiate.

Pre load or drag is a load or resistance keeping something from turning freely.

The most common measurement unit for tire pressure that stands for pounds per square inch. PSI is intended to measure the force exerted by the air inside a tire.

RPM is short for Revolutions Per Minute.

The Race, or cup as it is also called, is a press-in hardened surface for a bearing to ride on.

Tires built with perpendicular plies across the crown of the tire, effectively strengthening the tread for street driving. These tires also require belt plies going circumferentially around the tire for solidarity purposes.

A ratio is a quantity that denotes the proportional amount of one quantity relative to another.

The reverse rotation gear set was developed for use in front axle applications. The standard gear, when used in a front application, is running in reverse. This means the coast side of the gear is being used as the drive side. The convex (Drive) side of the gear is capable of carrying more load than the concave (coast) side. On a reverse ring and pinion, this problem has been corrected to create a stronger axle assembly. This was also done to help with driveline angles and reduce vi

The distance between bead seat to bead seat at bead seat radius.

The measurement between the flanges of a rim.

The Ring Gear, also known as a Crown Gear, is the gear that is bolted to the carrier and driven by the pinion gear, thereby turning the carrier.

The Root, or Flank, of a gear tooth is the very bottom or base of the tooth that spans the gap between the teeth.

Referring to a brake rotor, this is the part that the brake caliper clamps down on to slow the vehicle.

Run out is an undesired movement of a part through its motion, or wobble.

The distance between the sidewalls at the widest point of an inflated tire not under load.

A semi-floating axle is one that is supported at the inner spline end then is supported by a bearing before the outer end, carrying vehicle weight.

A shim is a thin piece of material used to fill small gaps or spaces between objects. Shims are typically used in order to support, adjust for better fit, or be used as spacers to fill gaps between parts.

The Side Gear is an internally splined gear that receives the axle shaft. The spider pinion gear then drives this gear.

The side portion of a tire between the tread and bead.

The Spanner is also known as a side bearing adjuster. This adjuster is used to move the carrier assembly side-to-side to set back lash.

A normal wrench with one open end and one closed end for fastening bolts or nuts.

Splines are the raised portions that look like teeth. Splines provide a strong and effective way of easily joining two parts together that will need to be removed at a later date. Splines are usually seen as an external (male) and internal (female) receiver variety.

A spool is used to permanently lock axles together. Spools are usually used in competition vehicles that require no differential action between the axles. Spools are not recommended for street use.

The steering knuckle is the main component that allows a solid axle to perform its steering function. The knuckle is usually retained to the housing by the ball joints or king pins.

The Stub Axle is the outer most axle shaft of a multiple shaft assembly.

Standing for short wheel base, usually found in either pickup trucks or SUVs with 3 doors, this refers to shorter wheel base vehicles where the distance between the front and rear wheels are around 90 inches. This often provide more maneuverability off-road, shorter turning circles and better break-over angle, but also are usually less stable on-road and at speed.

Also referred to as Drop Out. The drop out refers to a particular type of axle with a separate gear case assembly that can be removed from the housing (picture A). This is opposed to an axle that has the gears installed into the physical axle housing (picture B).

The Toe of the gear tooth is the inner half closest to the carrier. This is the part that sees pinion contact last.

Torque is the rotational force needed to move an object. In our case, it refers to the amount of force needed to turn a bolt or pinion. Torque is measured with a special tool called a Torque Wrench.

A Torque Wrench is a special tool that is used to measure the amount of force required to turn a bolt. This torque is measured in either in foot pounds or inch pounds depending on the quantity of force needed. There are a variety of different types of torque wrenches, but the two most common are the bar graph and the click types.

The distance from the top of the tread to the grooves in a tire. The measurement is taken at the centerline of a tire and is measured in thirty-secondths of an inch.

The arrangement of grooves, blocks, sipes, and channels on the tread of a tire that provide a varying degrees of effects on traction, tread life, and other tire factors.

The measured distance that extends from one bead seat to another across a wheel. The wheel diameter must be exactly the same as the tire rim diameter. Always make sure that the diameter stamped on the wheel and tire match exactly.

The distance between the inside of the rim flanges rounded to the nearest half inch that helps to ensure that the wheel width is the appropriate size for your tire. Each tire has a minimum and maximum wheel width limit.