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Off-Road Dictionary

A collection of common off-road related terms as presented by TeraFlex.

2WD - 2WD is the normal transfer case position selected when driving on the street and highway.

2WD Low - 2WD Low is an optional low range kit for the NVG 231 transfer case that disconnects the front drive output inside the transfer case offering the slow control of 4WD Low with the turning capabilities of 2WD. This is particularly useful when on tight trails that have a limited turning radius.

4WD High - 4WD High can be selected for all wheel traction at higher speeds (20-45 mph).

4WD Low - 4WD Low is selected for slow moving traction and control. This is the gear generally selected for trail driving and rock crawling.

Anti-Lock Brake System - Anti-Lock Brake System is a factory installed option on many vehicle which uses wheel rotation sensors to provide input to the vehicle computer and a control box. The system is designed to prevent wheel lockup during panic stops and when slowing down on slick surfaces.&

Air Down - To lower the air pressure in the tires to improve off-road traction.

Anti Sway Bar - The anti sway bar, generally referred to as a sway bar, prevents body roll and keeps the vehicle from swaying back and forth at highway speeds, this gives car-like handling characteristics. When off-road the sway bars will reduce articulation unless they are disconnected

Approach Angle - When viewed from the side of the vehicle, this is the angle between the ground an a line running directly to the lowest hanging part on your vehicle (usually the front bumper). This is the maximum angle that a vehicle can climb without hitting the front bumper or other component.

Articulation - Articulation refers to suspension flexibility that allows the vehicle tires to remain in contact with the ground while driving over uneven terrain.

Axle - The completed assembly of differential, shafts, bearings and seals necessary to transfer power from the driveshaft to the wheels.

Ball Joint - Ball joints mount the steering knuckle to the axle assembly inner C-Yoke, or to the IFS control arms. Ball joints allow the knuckle to pivot when steering the vehicle.

Back Spacing - The measured amount in inches from the inside mounting surface of the wheel to the inside lip of the wheel. Less backspacing means the wheel will stick out further from the vehicle.

Budget Boost - An economical way to lift your vehicle by using spring spacers or shackles.

Bump steer - Bump steer is when a vehicle pulls or shoots off to one direction as the suspension is compressed or extended (when going over bumps in the road).

Catalytic Converter - An emissions control unit in the exhaust system that helps to reduce harmful vehicle emissions.

CB Radio - Citizen's band radio allows an easy and inexpensive way to contact other vehicles when off-roading or in a convoy. They help to keep groups together and can be used to call out for help in emergencies.

Center of Gravity - The center position of balance of the vehicle from front to back and from the ground to its highest point. A lower center of gravity increases vehicle stability.

C-clip - The C-clip is used in Dana 35 and Chrysler 8.25” rear axles. The C-Clip is a retaining clip that holds the axle shaft into the differential carrier inside the axle housing. If the C-clip breaks or the shaft breaks, the axle shaft will be able to slide out of the vehicle. This can be very dangerous in off-road situations that are off camber, or vertical.

CJ - The CJ was the original open top four wheel drive vehicle capable of traversing just about any terrain imaginable. It first was introduced to the civilian market in 1945 and went through several model changes, some of which are the CJ-2A, CJ-5, CJ-7 and CJ-8. The last CJ model was produced in 1986 when it was replaced by the YJ Wrangler.

Coil Springs - An alternative to leaf springs for achieving desired vehicle height. Coil springs consist of multiple wraps of steel wire of a specific load rating.

Control Arm - The control arm is what holds the axle underneath the vehicle and keeps it located correctly under torque.

Crawl Ratio - The final low range ratio of your vehicle in 4WD low. This can be found by multiplying the transmission first gear ratio, transfer case low range ratio, and the axle ring & pinion ratio.

Curb Weight - The actual weight of a vehicle when loaded with fuel, driver, and passengers.

CV Drive Shaft - A common term used to describe a driveshaft with a double cardan joint to reduce vibration at steeper driveshaft angles on lifted vehicles.

Departure Angle - When viewed from the side of the vehicle, this is the angle between the ground and a line running directly to the lowest hanging part on your vehicle (usually the rear bumper). This is the maximum angle that a vehicle can descend without hitting the rear bumper or other component.

Differential - The differential transfers power from the driveshaft, through the axle shafts to the wheels. There are many different types of differentials such as; open, limited-slip, locking, etc. See Locker and Open Differential for more details.

DOM - DOM is the abbreviated name given to a specific type of steel tubing. Drawn Over Mandrel refers to the process that is used to manufacture the tubing. DOM tubing has superior strength and dependability characteristics compared to other types of tubing; specifically DOM is seamless.

DOT Approved - The Department Of Transportation must approve certain safety features of products (such as brake lines) if they are to be used legally on US streets and highways.

Drag Link - The drag link connects the pitman arm to the steering knuckle and enables the vehicle to turn via the steering wheel.

Drivability - This refers to a vehicle’s ability to drive under certain conditions, such as highway, off-road, gravel, dirt, etc. The main issues that are pertinent to drivability are: handling, steering, and ride quality. Depending on the modification, some aspects of drivability will be altered.

Driveshaft - The driveshaft transfers power from the transfer case to the axles.

Driveshaft Angle - The driveshaft angle is the angle that a driveshaft must be at to connect the transfer case to the axle. On lifted, short wheel base vehicles (SWB) the driveshaft angle can often be quite severe.

Full Float - An axle design where the vehicle weight is supported by a spindle and wheel bearing assembly. The axle shaft is used only to transmit power to the wheel through a drive flange or lockout hub assembly.

GVWR - Gross Vehicle Weight Rating is the maximum amount that the vehicle can weigh with full fuel, passengers and gear. This number is provided by the vehicle manufacturer and must not be exceeded.

High Center - High centering happens when all four wheels are off the ground and the vehicle is resting on its center skid plate. A high clearance skid plate like the TeraFlex BellyUP can help to reduce this problem.

High Pinion Axle - A high pinion axle housing design has the pinion shaft entering the housing above the axle tube centerline. The ring and pinion gear teeth are cut in the opposite direction to allow this relocation of the pinion shaft entry point. Sometimes this axle is mistakenly called a “reverse rotation” axle but this is not correct. The ring and pinion still rotate in the same direction but the tooth pattern is reverse cut allowing the driving force to be carried on the stronger side of the ring gear teeth when a high pinion axle is used in the front of a 4 wheel drive vehicle. When used in the rear of a 4 wheel drive vehicle some strength is lost since the driving force is applied to the weaker side of the ring gear teeth. For this reason many people choose to install a Heavy Duty 60 series axle such as the Tera CRD 60 in the rear of a light weight vehicle.

IFS - Independent Front Suspension refers to a vehicle suspension design where the front knuckles mount to the frame through ball joints and some type of upper and lower A-arms. This design allows either side to travel up and down independent of the opposite side. IFS has been used for many years in cars, and is now common in 4 wheel drive vehicles.

Knuckle - The knuckle connects the wheel assembly to the axle housing inner knuckle or C-Yoke through 2 pivot points and creates a mounting point for axle components such as tie rods, unibearings or hubs, brakes, etc.

LCA - The lower control arm is a suspension component that connects the axle to the frame of the vehicle. These can be lengthened and shortened to fine tune alignment and pinion angle.

LCG - Low Center of Gravity.

Leaf Spring - The most traditional suspension design until the mid 1990’s. Leaf springs utilize an arched steel strap that is heat treated and combined into a multiple leaf pack to give the vehicle its intended height. Leaf springs are very stable and offer a relatively stiff ride.

Locker - A locking differential provides equal torque to the vehicle’s wheels by forcing both axles to turn at the same speed. A selectable locker like the TeraFlex T-Locker can be turned on or off with a switch and allows open differential driving while on the road, and a locked differential when off-roading.

Long Arm - Lower long arms increase the arm length by almost double in most cases, and will provide the vehicle with increased on road drivability and off road articulation.

LWB - Long Wheel Base vehicles generally have over 100” of wheelbase. This includes the Cherokee, and Grand Cherokee.

Nodular Iron - Nodular Iron (Ductile) is a cast iron that has been treated while molten with an element such as magnesium or cerium to induce the formation of free graphite as nodules, which imparts a measurable degree of ductility to the cast metal. Nodular iron is commonly used in casting automotive differential housings.

OEM - Original Equipment Manufacturer is the supplier of equipment that came stock on a vehicle or was specified by the factory for production vehicles.

Open Differential - An open differential allows different wheel speeds for smooth turns on high traction surfaces. This is great for driving on the road, but in low traction situations the open differential allows all vehicle torque to be transmitted to the wheel with the least amount of traction.

Pitman Arm - The pitman arm connects the steering box to the drag link. On lifted Jeeps a drop pitman arm is usually needed to restore proper steering linkage geometry.

Ring & Pinion - The ring and pinion transfer power from the driveshaft to the axle shafts. Ring and pinions come in various ratios to allow the wheels to turn at a different rate than the transfer case. Ring and pinions consist of a smaller gear (pinion) which turns a larger circular gear (ring).

Revolver Shackle - The Revolver Shackle is a unique shackle that is hinged to allow additional articulation and down travel. It also will help to reduce leaf spring stress when under articulation.

Rock Crawler - A purpose built 4x4 vehicle to crawl over rocks and boulders.

RTI - RTI or ramp travel index is a measurement of a vehicle’s suspension flex or articulation. This can help to show areas that need attention before the vehicle is taken off-road, or to measure for new components such as shocks or brake lines.

Semi-Float - An axle shaft that transmits the vehicle’s power or torque to the wheel, and carries a portion of the vehicle’s weight. A semi-float axle shaft is held into the axle housing with a wheel bearing retainer plate or C-clip.

Short ShaftA slip yoke eliminator or short shaft kit replaces the transfer case output shaft with a much shorter shaft that accepts a fixed yoke and seal assembly. This allows the use of a CV driveshaft that is longer and can handle a more severe driveshaft angle caused by increased vehicle lift.

Solid Axle - A solid axle refers to the complete differential housing that is rigid from axle flange to axle flange (or knuckle to knuckle). The solid axle has many features that are desirable for off-roading such as increased articulation potential.

Spring Rate - Spring rate is measured by the force required to compress the spring one inch. For instance a spring with a spring rate of 220 requires 220 lbs. to compress the spring one full inch.

Steering Box - The steering box transfers the movement of the steering wheel to the wheels through the pitman arm, drag link and tie rod.

SWB - A short wheel base vehicle has less than 100” of wheelbase. This includes TJ and YJ Wranglers and CJs.

Tie Rod - The tie rod is part of the steering linkage, connecting both knuckles on a steering axle allowing the vehicle to turn. A bent tie rod is a common failure on the trail and results in your tires being excessively ‘toed-in’.

Triangulated Suspension - A suspension design that uses control arms that when viewed from the top appear in the shape of a triangle. The opposing direction of the arms controls the side to side movement of the axle and allows the track bar to be eliminated.

TJThe TJ Wrangler has been produced since 1997. It features coil springs, and arguably a better on road and off-road ride. It replaced the YJ Wrangler.

Torque - A force that turns or twists resulting in rotation. Torque is measured in ft. lbs. (US)

Track Width - The measurement from right tire to left tire centerline. Track width can be modified in several ways, some of which are new axles, new wheels, and wheel spacers. A wider track width can help to make your vehicle more stable on side hills and uneven terrain.

Track Bar - The track bar locates your axle side to side underneath the vehicle. The track bar must be modified or relocated when the vehicle is lifted to compensate for the additional lift. If it is not re-located the axle will be offset from the center of the vehicle and can result in adverse handling characteristics.

Transfer Case - A gearbox that allows the power from the transmission to be transferred to both the front and rear axle equally. It also allows the driver to shift from 2WD high to 4WD high, and 4WD low

Turning radius - This is a measurement of how sharp a vehicle can turn. The smaller the number the tighter the vehicle can turn. This can be very important on some trails that have very little room to move.

UCA - The upper control arm connects the frame to the axle and can be lengthened or shortened to fine tune the alignment and pinion angle.

U-Joint - Short for universal joint, the u-joint is a coupling device that connects the drive shaft to the yoke and allows the drive shaft to operate at an angle. U-joints are also used in front steering axles to connect the inner axle shaft to the outer axle shaft or stub shaft, and allow the vehicle to turn and still transfer power to the wheels.

Wheel Base - Wheelbase is the measurement from the center of the front wheel to the center of the rear wheel in inches.

Wheel Travel - The measured amount that each wheel can travel between full extension and full compression.

WJ - The WJ Grand Cherokee is a redesigned version of the ZJ Grand Cherokee and has been produced since 1998. It features a coil spring suspension front and rear.

XJ - The Cherokee was one of the original sport utility vehicles (SUV) and arguably created the SUV market that exists today. The Cherokee was produced in the XJ form from 1984 until 2001. It featured a front coil spring suspension and a rear leaf spring suspension. It remains one of the most popular off-road vehicles for modifications today.

YJ - The YJ was manufactured from 1987 through 1995. It replaced the CJ line of open top off road vehicles, and was replaced by the TJ wrangler. It has a leaf spring suspension.

Yoke - Yokes connect the drive shafts to the transfer case and axles via u-joints. 2 yoke styles are used. One style uses straps and small head bolts and the other uses u-bolts with washers and nuts to secure the u-joint.

Z-Box - The Z-Box replaces the factory leaf spring mount on the vehicle frame. The Z-Box opens up during axle droop and works in conjunction with the Revolver Shackle to reduce spring stress and maintain proper driveshaft angles. The opposing construction allows only one side to open at a time.

ZJ - The ZJ Grand Cherokee was produced from 1993 until 1997 when it was updated and introduced as the WJ. The ZJ features a coil spring suspension front and rear making it very capable on and off-road.

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