Common terms and definitions ...

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4-Wheel Drive

Also, 4WD. A drive train in which all of the wheels of the vehicle are driven simultaneously. While '4-Wheel Drive' (4WD) and 'All Wheel Drive' appear functionally the same, they are not. There are two primary points of distinction. 4-Wheel Drive's additional gear reduction besides that supplied by the transmission and the machanical restriction of 4-Wheel Drive systems to loose or slipery surfaces.

4-Wheel Drive systems can be split into two general catagories: part time and full time. Part time 4WD systems utilize a method to lock the front and rear axles in sync, thus operating in a simalar fashion to the Locking Differential in an axle. Full time 4WD systems are effectivly 'All Wheel Drive' with additional gear reduction besides that supplied by the transmission. Full time 4WD systems are an attempt to provide the best of both worlds - All Wheel Drive on the highway with true 4-Wheel Drive off road.

9 Inch

Slang. A term used to refer to the Ford 9-Inch differential. '9 Inch' refers to the width of the ring gear in inches.

10 Bolt

Slang. A term used to refer to the General Motors (GM©) 10 bolt differential. '10 Bolt' refers to the number of bolts that attach the differential cover.

12 Bolt

Slang. A term used to refer to the General Motors (GM©) 12 bolt differential. '12 Bolt' refers to the number of bolts that attach the differential cover.

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A/T

1. Acronym. All Terrain. A term used to describe a type of tire primarily designed for state and federal highway use but agressive enough for moderate use off road. All Terrain tires are designed to provide better manners (longer life, lower noise, lower vibration, plusher ride) on the highway while sacrificing off road performance.

2. Acronym. Automatic Transmission.

Air Down

The process of decreasing tire pressure to increase traction, improve flotation and improve ride quality when off road and traveling over rough terrain. Traction and flotation are improved by increasing the tire's 'Contact Patch' area. Traction improvements are also seen as the result of the tire's increased ability to 'wrap' around an object.

All Wheel Drive

A drive train in which all of the wheels of a vehicle are driven simultaneously. While 'All Wheel Drive' and '4-Wheel Drive' appear functionally the same, they are not. There are two primary points of distinction. All Wheel Drive's lack of additional gear reduction besides that supplied by the transmission and All Wheel Drive's ability to be used continuously on any road surface.

Anti-dive

A measurment of how well a vehicle's front suspension resists 'Dive'.

Anti-squat

A measurment of how well a vehicle's rear suspension resists 'Squat'.

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Contact Patch

The area of a tire in contact with the ground. For example, if a tire were lifted off the ground, machinists dye was painted on the tread, a sheet of paper was then sliped between the ground and the tire, and the vehicle was then lowered back to the ground, the area on the paper delineated by the dye would be the 'Contact Patch'.

Crawl Ratio

The combined gear ratio of an off road vehicle. The 'Crawl Ratio' is calculated by taking the lowest ratio of all the gear reduction systems in a vehicle and then multiplying them together.

Crawl Speed

The time in seconds or minutes it takes an off road vehicle to travel X distance in feet or inches.

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Differential

An assembly of gears arranged to allow at least two shafts to turn at different speeds. The term is most commonly used to refer to the 'pumpkin', or differential assembly in a 'Solid Axle' or 'Independent Suspension' assembly.

Dive

The tendency for the front of a vehicle to nose down or 'dive' durring compression braking such as on steep decents or when braking normally on the street or trail.

DOM

Acronym. Drawn Over Mandrel.

DOT

Acronym. Department of Transportation. Generally used to refer to the Federal department.

Doubler

A preassembled product or kit installed between the transmission and transfer case used to further multiply the gear ratio over the lowest ratio available in the transmission. This is not a transfer case as it has no front output, only one gear ratio and is typically either engaged or disengaged. The term 'doubler' is somewhat misleading since rarely is the gear ratio actually 'doubled' or 2:1. The term 'doubler' it commonly used to refer to D&D Machine's Doubler products.

Drag Link

Part of the steering assembly. The link that runs from the Pitman arm on the steering box to the steering arm on the axle or the tie-rod in the case of Y or T steering systems.

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ECM

Acronym. Engine Control Module. See also 'ECU'.

ECU

Acronym. Engine Control Unit. The computer module responsible for ingesting the data from the various engine sensors; then uses the data to control the various operations of the engine such as timing and fuel control. In error, the terms ECU/ECM and PCM are often used interchangably. An ECU is responsible for engine functions, while a PCM, in addition to handling engine functions, also manages power train functions which may include such things as ABS, traction control, and transmission control. See also 'PCM'.

Effective Gear Ratio

The final gear ratio as measured at the ground. The calculation is based on the transmission, transfer case, reduction box (if present), differential and tire size.

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Farm Jack

Slang. A term sometimes used to refer to a Hi-Lift Jack© style jack.

Floatation

A measurment of how well a tire will travel over soft terrain such as snow and sand without sinking in.

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Hi-Lift

The name of the company that produces the Hi-Lift Jack©. Also, a common abbreviation of Hi-Lift Jack©.

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IAC

Acronym. Idle Air Control. The valve that regulates idle speed on a fuel injected engine by controling the the amount of bypass air ingested by the engine.

Independent Suspension

A suspension system wherein the two opposing wheels are independently attached to the chassis thereby allowing each wheel to act independently of the other.

IFS

Acronym. Independent Front Suspension. Opposing front wheels can move independently of each other irrespective of the terrain.

IRS

Acronym. Independent Rear Suspension. Opposing rear wheels can move independently of each other irrespective of the terrain.

ISC

Acronym. Idle Speed Control. See also 'IAC'.

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Jacking

Also, Chassis Jacking. The effect of one end of the chassis/body of the vehicle being forced up, away from it's respective axle by the driving force applied to that axle. Typically seen in vehicles utilizing some type of link or radius arm suspension.

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Live Axle

The drive axle in a vehicle equipped with 'Solid Axles'.

Locking Differential

Also, Locker. A 'Differential' with the capability to machanically connect or 'lock' both outputs together so that the driving force is distrubuted to each output evenly. Unlike a standard or 'Open Differential', if one output is allowed to free wheel the opposing output will continue to turn.

Locking Hub

A device used to connect/disconnect the axle shaft from the wheel. There are two types of locking hub - manual and automatic. The manual hub requires a person to exit the vehicle and engage or disengage the hub by hand and are generally found on vehicles without 'shift on the fly' 4-wheel drive. The automatic hub locks and unlocks without user intervention when the vehicle is shifted into and out of 4-wheel drive and is commonly part of a 'shift on the fly' 4-wheel drive system.

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M/T

1. Acronym. Mud Terrain. A term used to describe a type of tire primarily designed for off road use but still legal for use on state and federal highways. Mud Terrain tires are designed to provide better off road performance while sacrificing highway manners (more noise, lower traction, lesser life span, more vibration, harsher ride).

2. Acronym. Manual Transmission.

MAF

Acronym. Mass Air Flow. A sensor used to measure the amount of air being ingested by an engine.

MAP

Acronym. Manifold Absolute Pressure. A sensor used to measure the pressure inside an engine's intake manifold.

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Off-camber

A trail that tilts either to the left or right. i.e. Not horizontal.

Open Differential

The most common and most basic type of 'Differential'. The driving force is distrubuted to each output evenly until either output free wheels, at which point the driving force is directed to the free wheeling output.

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Panhard Bar

A component of a suspension system that provides lateral location of a 'Solid Axle'.

PCM

Acronym. Powertrain Control Module. The computer module responsible for ingesting the data from the various engine and powertrain sensors, units that may control such things as ABS, transmission shift points, traction control, etc.; then uses the data to control the various operations of the engine such as timing and fuel control, and other functions such as traction control and the transmission. See also 'ECU'.

Pull-down Winch

A small winch attached to the front or rear of the chassis of a vehicle. The cable or rope of the winch is then attached to the axle. Used to prevent or control chassis 'Jacking'.

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Rolling Radius

The radius of a tire measured from the ground to the center of the axle shaft with the vehicle on the ground, the tire mounted and installed on the vehicle and inflated to the desired operating pressure.

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Shelf Road

A narrow road or trail with a vertical or near vertical wall on one side and a sheer drop on the other side.

Shift on the Fly

A 4-wheel drive system that allows the driver to shift into and out of 4-wheel drive without stoping the vehicle.

Slick Rock

A term used to describe any large expanse of relatively smooth, unbroken rock but is most commonly used to describe the expanses of sandstone in and around southern Utah - more specifically, in and around Moab, Utah.

The term was originally coined by Mormon settlers navigating the Mormon Trail to describe the unending expanses of slipery, bare rock they needed to cross with their wagons. The steel rimed wagon wheels had almost no traction on the rock and slid around (at times) uncontrolably, hence the term 'Slick Rock'.

Snatch Block

A pulley-block that can be opened to receive the bight of a rope. An important piece of recovery equipment primarily used for complex pulls or for multiplying the pulling capacity of a winch or Hi-Lift Jack©.

Snatch Strap

A recovery device. Typically a long nylon web strap with reinforced loop eyes at each end. Not to be confused with tow strap which typically has hooks at each end and is shorter per 'DOT' specifications.

Solid Axle

Opposing wheels are directly connected to each other via a solid housing, thus the terrain an opposing wheel is traversing at the moment directly affects its opposite.

Spooled Differential

A 'Differential' with both outputs machanically connected, or 'locked' together so that the driving force is distributed to each output evenly. Unlike a 'Locking Differential', a Spooled Differential can not be unlocked.

Squat

The tendency for the rear chassis/body of a vehicle to sink or settle towards the ground durring accelleration or when making steep accents.

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Tie Rod

Part of the steering assembly. The link or links that connect or 'tie' the wheels into the steering.

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Wheel Recession

When the front wheels are placed against a vertical face, the tendency for the wheels to want to dig under the face rather than climb over.

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