Approach Angle

Starting from level ground, this is the degree of slope a vehicle can approach without scraping or hitting the front undercarriage. It's a great indication of the ability to navigate severe off-road terrain like boulders and logs. A short front overhang produces high angles of approach, thus increasing off-road ability.

Articulation

A Trail Rated® suspension is limber like a gymnast. How, exactly? Flexibility is the key to good articulation. The more a wheel can travel, or flex, the better it can maintain contact with the ground and provide the traction needed to cross an array of obstacles.

Axle Articulation

The ability of one axle to move relative to the chassis. It is the measure of the ease with which tires stay in contact with the ground (and retain traction) on very uneven terrain.

Axle Differential

An axle differential is a gear system located in the centre housing of an axle assembly designed to allow the wheels to rotate at different speeds during cornering.

Axle

A shaft that connects the front and/or rear wheels together. The suspension components attach to the axle and to the vehicle’s body frame. 

Brake Traction Control System

Transfers torque from one wheel to another on the same axle when wheel slip conditions are detected.

Breakover Angle

This off-road term refers to the degree of slope that defines the largest ramp or hill that a vehicle can travel over without scraping against the frame or underbody components.

Centre Differential – Geared

A gear system located inside the transfer case of full-time 4x4 vehicles. It is used to distribute drive torque to the front and rear driveshafts and allows the front and rear wheels to rotate at different speeds during cornering.

Clutch Plates

A series of alternating steel plates within the transfer case of many on-demand or automatic 4x4 systems. One set of plates is splined to the clutch assembly hub of the rear driveshaft; the other set is splined to the clutch drum attached to the front driveshaft. The clutch housing is usually filled with a viscous, silicone-type fluid that clings to the discs to help transfer torque to the driveshaft. The engagement of clutch plates can also be controlled electronically.

Coil Springs

A coil of flexible metal that can be compressed or stretched along its centreline axis without permanent deformation. Coil springs support the weight of the vehicle while allowing the wheels to travel up and down over bumps.

Continuously Variable Transmission (CVT)

A stepless transmission that uses a sheave clutch to transmit engine torque.

Crawl Ratio

Essential for serious off-road treks involving steep hill climbs and descents, this is the final drive ratio of a vehicle in low range. It allows Jeep® vehicles to creep along (without depressing the accelerator) at very low speeds. Essentially, the vehicle does all the work. Except with Freedom Drive II® on Patriot and Compass, crawl ratio is determined by this formula: first gear ratio x rear axle ratio x low-range 4-wheel-drive ratio. The higher the number, the better the off-road capabilities. With Freedom Drive II on Patriot, the crawl ratio is a special fixed CVT ratio of 19:1.

Crow Hop

Vehicle shudder and tire scuffing due to a binding condition in the driveline, which is usually caused by operating in basic 4-wheel-drive or part-time 4-wheel-drive modes on dry pavement.

Departure Angle

When returning to level ground from a descent, this angle indicates the degree of a slope from which a vehicle can depart without scraping or hitting the rear undercarriage.

Differential

A gear system that transmits torque to the drive wheels, while also allowing the wheels to rotate at different speeds when cornering. Vehicles with 4-wheel drive have differentials in both the front and rear axles.

Driveshaft

Shaft connecting the transmission output shaft to the differential drive pinion shaft. Vehicles with 4-wheel drive add a second driveshaft from the transfer case to the front differential. 

Electronically Controlled Coupling

Manages the torque split from front to rear with no active driver input needed, for smooth and automatic performance. It responds to throttle position or to front wheel slippage.

Fixed Yoke Output Assembly

Effectively handles the extra output from the transfer case and helps to ensure smooth and durable driveline operation.

Four-Wheel Drive

A drivetrain that utilizes a transfer case or Electronically Controlled Coupling to distribute engine power between the front and rear axles in order to drive all 4 wheels. Full-time 4-wheel-drive systems utilize a centre differential, which enables the front and rear driveshafts to turn at different speeds, thereby allowing engagement on dry pavement for normal driving conditions. A part-time system does not employ a centre differential and, during normal driving conditions, must operate only in 2-wheel drive. With a part-time system, the 4-wheel-drive mode is to be used only when off-roading or on wet or slippery surfaces.

Front Axle Disconnect

A mechanical or vacuum-operated component used primarily on 4x4 models to connect and disconnect drive torque to the front axle. When shifting from 4-wheel drive to 2-wheel drive, this system disengages the front axle from the front driveline so that the front wheels aren't turning the front driveline unnecessarily. This reduces unnecessary front driveline wear, noise and fuel consumption.

Ground Clearance

Don't drag your belly through the mud – just clear nasty logs, rocks and uneven ground without sustaining undercarriage damage. Jeep® Trail Rated® 4x4 vehicles feature optimized approach, departure and breakover angles to keep you in the clear.

High-Range

A 4WD mode used for on-road or light off-road use.

Hill Descent Control

This system uses the ABS braking to control the car's motion downhill. It also allows a smooth and controlled hill descent in rough terrain without the driver needing to touch the brake pedal. If the vehicle accelerates without driver input, the system will automatically apply the brakes to slow down to the desired vehicle speed.

Jounce/Rebound

The motion of a wheel that compresses its suspension. If a wheel is at full jounce, it is at the upper limit of its travel. The opposite of jounce is rebound, or wheel movement that decompresses a vehicle's suspension.

Limited-Slip Differential

Provides the same basic functions as an axle differential, but with an added advantage: when the drive wheel begins spinning as a result of being on a slippery surface, a limited-slip differential automatically transfers torque to the opposite wheel to help improve traction. 

Locking Differential

Provides even more traction than a limited-slip differential in tough conditions by locking the axle shafts together. Locking differentials do not allow for wheel-speed differences and must not be used on dry, paved roads.

Low Crawl Speed

The crawl ratio is the lowest gear ratio in a vehicle and is determined by multiplying the first gear ratio by the low-range ratio by the axle ratio.

Low Range

A 4WD mode used for severe off-road conditions.

Manoeuvrability

Athletic. Agile. Trail Rated®. Jeep® 4x4 vehicles have the footwork to navigate narrow gaps, dodge emergency situations and avoid cosmetic damage to underbody sills, thanks to precision steering and optimized wheelbases. 

Neutral

When the shifter is in this position, the front and rear axles spin freely. Sometimes used for towing a Jeep® vehicle behind another vehicle (such as a motor home), so that uncoupling the driveshafts is not required. Also used in the process of shifting into 4WD LOW.

Open-Centre Differential

Located in the transfer case on some full-time 4x4 vehicles, this component works in the same way as an open differential in the axles but is of a more compact design. This component employs a planetary gearset, with planetary gears that revolve around the sun gear and inside the ring gear.

Power-Robbing Friction

Surface resistance to relative motion, as of a body sliding or rolling.

Running Ground Clearance

The distance from the ground to the lowest point between the axles.

Shift-on-the-Fly

The ability to shift from 2-wheel drive to 4-wheel drive while the vehicle is moving.

Skid Plate

Helps protect the undercarriage from damage when driving off-road.

Solid Axle/Coil Springs

Ideal off-road equipment. Instead of each wheel on an axle being sprung separately (like independent suspension designs), a solid axle connects the suspension of 2 wheels. Coil springs then support the vehicle's weight and allow the wheels to travel up and down over terrain.

Suspension Travel

From full jounce to full rebound, this is the amount of vertical wheel movement allowed by the suspension.

Tow Hooks

Heavy-duty forged steel hooks, in the front and rear of a vehicle, that provide attachment points for snatch-em straps and winch cables should you get stuck.

Traction

Traction in 4x4 is equivalent to grip on asphalt. Trail Rated® traction helps you stay in control on untamed terrain, in slippery (wet, mud, snow) conditions, and on steep grades.

Transfer Case

Mounted behind and driven by the transmission on most 4x4 vehicles, the transfer case transmits power to the front and rear driveshafts in 4x4 Jeep® vehicles and offers high and low range. Compass and Patriot 4x4 use an Electronically Controlled Coupling instead of a traditional transfer case.

Transmission

A mechanism that transfers torque into usable driving power, usually through the use of gearsets. These gearsets multiply engine torque in varying amounts to meet specific driving demands. An exception is a Continuously Variable Transmission (CVT), available on Compass and Patriot, which instead operates by varying the working diameters of 2 pulleys, transmitting torque by means of an immensely strong, steel-segmented push-belt.

Two-Wheel Drive

When the shifter is in this position, the front axle spins freely while power is sent to the rear axle and wheels, which then drive the vehicle.

Viscous Coupling

A speed-sensitive device located in the transfer case that transmits drive torque between the front and rear driveshafts when wheel slip occurs. Viscous couplings are typically used on all-wheel-drive vehicles and vehicles with automatic and on-demand 4x4 systems.

What is the difference between full-time 4x4 and part-time 4x4 systems?

Full-time 4x4 systems utilize a centre differential, which enables the front and rear driveshafts to turn at different speeds, thereby allowing engagement on dry surfaces for normal driving conditions. A part-time system does not employ a centre differential and locks the front and rear driveshafts together. With a part-time system, 4x2 mode should be used during normal driving conditions and 4x4 mode is to be used only when off-roading or on wet or slippery surfaces.

Why can't you use part-time 4x4 on dry surfaces?

Part-time 4x4 systems effectively lock the front and rear driveshafts together, forming a single driving unit that does not allow for differential action between the front and rear driveshafts. Driveline noise and binding (Crow Hop) may occur when operated excessively on dry surfaces or in turns. This binding can lead to heat buildup and early part failure.

Why does Crow Hop occur?

When a vehicle turns, each wheel rotates on a different radius to the turning circle, thereby travelling different distances at different speeds. If the vehicle's front and rear axles are locked together and are turning on dry surfaces, the difference in wheel speed sometimes results in driveline binding that is released with a bang or vehicle shudder when one of the tires loses traction.

Can I shift into 4WD high range at any speed?

Shifting into 4WD high range can be done with the vehicle stopped or in motion. If the vehicle is in motion, shifts can be made up to 88 km/h (55 mph).

How long can I drive in 4WD high range?

With a part-time system, prolonged driving in 4WD high range is recommended only for wet, loose or slippery road surfaces. With a full-time system, you need not worry about switching to 2WD mode when road surfaces improve.

How fast can I drive in 4WD high range?

You should not go faster than road conditions permit.

What is 4WD low range?

4WD low range is a mode specifically designed for temporary use when additional traction and maximum pulling power are desired. Front and rear driveshafts are locked together and engine power is sent through another set of gears to multiply torque. Avoid attempting to engage or disengage low range with the vehicle moving faster than 3–5 km/h (2–3 mph), and do not use this mode for normal driving.

Can I shift into 4WD low range at any speed?

No. With the vehicle rolling at 3–5 km/h (2–3 mph), shift an automatic transmission to Neutral or depress the clutch pedal on a manual transmission. While the vehicle is coasting at 3–5 km/h (2–3 mph), shift the transfer case lever firmly through Neutral and into the low range position.

How fast can I drive in 4WD low range?

Do not exceed 40 km/h (25 mph).

Can I shift into 4WD low range when stopped?

Shifting into or out of 4WD low range is possible with the vehicle completely stopped; however, difficulty may occur due to the teeth of the gears not being properly aligned. Several attempts may be required for clutch teeth alignment and shift completion to occur. The preferred method is with the vehicle rolling at 3–5 km/h (2–3 mph). Avoid attempting to engage or disengage 4WD low range with the vehicle moving faster than 3–5 km/h (2–3 mph).