Off-roading Terms

Listed below are some common off-roading terms for those just entering into the 4x4 off-roading world compliments of FourWheeler.com and Woodpark-offroad.com.

ABS. Anti-lock braking system; prevents wheels locking under maximum braking. Works on the principle of braking a wheel until it just begins to skid (this is the point where braking efficiency would drop off dramatically) and then releasing the brake pressure and re-applying the brakes. Wheel speed sensors identify the skid point and trigger a release in brake pressure. The cycle is repeated many times a second -with appropriate 'cobblestone' feed-back on the brake pedal to indicate you are in ABS mode. See also 'Cadence braking'

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

Air Locker: A brand of locking differential from ARB. It acts like an open differential until it’s actuated by compressed air. Then it completely locks, causing both tires to rotate at the same speed regardless of traction.

Approach angle. In side-view, the angle between the ground and a line, ahead of the vehicle, joining the periphery of the front wheel and (typically) the front bumper or other low component. It represents the size or steepness of a slope or obstacle that can be approached or climbed without striking bodywork.

Armor-clad: Slang for a vehicle that is equipped with heavy-duty skidplates for the undercarriage or body protection.

Articulation. The ability of one axle to move - left wheel up, right wheel down or vice versa - relative to the chassis or its fellow axle. It is a measure of the ease with which wheels can stay in contact with the ground - and thus retain traction - on very 'twisty' off-road terrain.

Articulation angle, longitudinal. See 'Longitudinal articulation angle', wheels run within rigid casings without joints to allow vertical hinging as with independent suspension. In an off-road vehicle rigid axles have the advantage of maintaining maximum under-axle ground clearance at all times and always keeping the tyre tread flat on the ground.

Basket Case: An engine or vehicle that is in pieces

Beater: A thrashed and very ugly truck that is usually mechanically sound. In some circles, this is used as a derogatory term, but in four-wheeling it can be a term of respect.

Beefing: A general term used to describe modifying a stock part or vehicle to be stronger. An upgraded part or truck can also be referred to as beefed-up.

BOG: (1) The large pit of mud at a mud-bog race. (2) Running an engine below its intended rpm range by being in a gear that is too high for the speed or load.

Bomber: Another word for a beater, although this usually refers to a poorly running beater.

Biscuit: Slang for body bushings used to lift the body of the vehicle from the frame to gain ground clearance. They are also referred to as donuts.

Bridle. A rope or cable attached to two points - typically the right and left chassis members - of a vehicle and converging to a point of attachment for a tow rope.

Bulletproof: When a truck or part is upgraded or modified so that it is extremely strong.

Cadence braking. A method of manual braking with the foot brake to simulate the action of ABS brakes - see above. Very effective in slippery conditions where brake locking has occurred or might otherwise occur, the driver applies the footbrake in a series of very rapid jabs at the pedal taking the wheels up to the point of brake locking and then releasing them before the inevitable fall-off in braking efficiency takes place. Effects improved braking in any extremely slippery conditions such as ice, snow, wet mud, or rain

Capstan winch. A winch, generally mounted on or just behind the front bumper, usually run from an engagable extension to the engine crankshaft. The active component is usually a slowly revolving drum, about 15 cm in diameter, round which a rope may be wound to effect a winching operation. Has the advantage of being powered by the engine at idling speed and being a very low-stress unit that may be used all day without overheating or high electrical load.

Castor (or caster) angle. When the front wheels are moved right or left to steer the vehicle they each move about a steering axis. The aft inclination of this steering axis from the vertical (when viewed from the side) - about in the case of most Land Rovers - is the angle. Like casters on a tea trolley or office chair, this puts the ground contact point of the wheels the pivot axis and the result is a self-centering action tending to keep the front wheels pointing forward when in forward motion. Note that in deep sand with a 'bow wave' build-up of sand ahead of the wheels the effective ground contact point moves ahead of the steering axis and can give the effect of negative castor with runaway' steering. The same thing happens when vehicle is travelling in reverse - the ground contact point being 'ahead' of the steering axis and again tending to make the front wheels 'run away' to full lock, failed climbing of steep off-road inclines.

Castor action. Tendency of front wheels to self-centre when the steering wheel is released with the vehicle going forward. NB Opposite action takes place when in reverse - see Castor angle above. Castor action is a basic ingredient of steering feel.

Centre differential. A differential gear device installed at the point where the transfer box splits engine power between the front and rear axles via the front and rear propeller shafts. Working in the same way as the conventional rear axle differential on a two-wheel drive car, it allows differential rotation of front and rear shafts to accommodate the small rotational differences encountered in normal running, going round sharp corners etc. Such a device is essential in a vehicle having - for use on-road as well as off-road - full-time or permanent 4x4. Vehicles fitted with part-time or selectable 4x4 are not fitted with centre differentials and thus cannot be used in four wheel drive on hard roads.

Continuous rolling contact. Description of a wheel in steady rolling contact with the ground without slip, wheel-spin or slide (as with locked brakes). Should be the aim at all times both on and off road.

Cornbinder: Slang for any truck made by International Harvester because the company is known for its farming equipment. These trucks are also referred to as ’Binders.

Crawl Ratio: The lowest gear ratio in a truck, found by multiplying the First-gear ratio times the low-range ratio times the axle ratio.

Cross ply tyre. Tyre in which the sidewall reinforcement plies run diagonally from the bead towards the tread - each layer of textile at a different angle to its adjacent layer. Generally superseded by radial-ply tyres whose thinner, more flexible sidewalls and braced tread yield better grip and lower rolling resistance. Because of thicker, multi-ply sidewalls, not so prone to sidewall damage as radials and can have low-cost applications when operating continuously on rock. However, reduced pressures in soft going can, due to the thick sidewalls, cause overheating and possibly de-lamination of the tyre.

Co-ordinated tow. When recovering a stuck vehicle, the process by which the engine power of both the tug and the stuck vehicle are co-ordinated - usually by a signal from an external marshaller - and the clutches of both vehicles are engaged at the same time to enhance the chance of a first-time recovery.

Corrugations. Deformation of an unsurfaced track taking the form of transverse, close-pitch undulations - ie at right angles to the direction of the track. Sometimes referred to as 'washboard'.

Coupled brakes. Brake system installed with certain large trailers whereby the trailer brakes are applied at the same time as are the brakes of the towing vehicle. Vehicles must be specifically modified to operate this system - with appropriate trailers.

Departure angle. In side view, the angle between the ground and a line, aft of the vehicle, joining the periphery of the rear wheel and (typically) the rear chassis member or other low component. It represents the size or steepness of a slope or obstacle that can be approached or climbed in reverse without striking bodywork.

Diagonal suspension. A manifestation occurring off-road when a vehicle is, for example, diagonally crossing a small but well-defined ridge. When the ridge is so severe that, say, the right front wheel and the rear left wheels are on full 'bump' (ie fully up in the wheel arches) and the other wheels are hanging down to the full extent of wheel travel, the vehicle may be described as being diagonally suspended or on diagonal suspension. Some also refer to this state as being 'cross-axled'.

Diagonal wheel-spin. The wheel-spin that can take place on the fully extended wheels in a condition of diagonal suspension as described above. However, a vehicle need not be in a totally diagonal suspension condition for diagonal wheel-spin to take place; minor off-loading of diagonally opposed wheels or the presence of slippery ground under these wheels can provoke the condition. Can also occur crossing ditches diagonally;

Diff-lock. See first 'Centre differential' above. Locking of the centre differential, activated by moving the transfer gearbox lever to the left and confirmed by illumination of the 'DIFF-LOCK' indicator light, puts the differential function on hold. Where traction conditions or grip are different front and rear there would be a tendency for the centre differential to permit the front wheels, say, to spin ineffectively while they are on wet clay and cause the rear wheels, on grippier ground, to stop rotating. The diff-lock locks the centre differential, thus locking front and rear prop shafts together, ensuring they revolve at the same speed and enhancing traction. Diff-lock is usually engaged for difficult off-road conditions but should never remain engaged on hard grippy roads.

Differential casing. Not to be confused with the centre differential, each axle, of course, has a normal cross-axle differential at the point where the propeller shaft from the transfer gearbox meets the axle. The size of the crown wheel and pinion plus differential demands a bulge in the axle casing - referred to as the diff casing. It has special significance in off-road vehicles because it is the lowest point of the axle and thus the point of least ground clearance -

Discontinuity of rolling contact. Generic term for wheel-spin and wheel slide - as on locked brakes. See 'Continuous rolling contact' above.

Double-line: To route the winch cable from the vehicle to a snatch block, then back to the vehicle. This doubles the pulling power of the winch but cuts its speed in half.

Droop: Downward suspension travel.

Dropped Pitman Arm: An aftermarket part that extends farther to the steering linkage than the stock arm. It corrects steering geometry by reducing the drag-link angle in relation to the tie rods on lifted 4x4s. A pitman arm connects
the steering box to the truck’s steering linkage.

EAS - electronic air suspension. Introduced in the 1993 model year on certain Range Rover models further to enhance standards of road noise insulation, ride and handling, the system substitutes air bags and a live-line pneumatic system, (ie an electrically driven compressor, air pressure reservoir and associated controls) for the steel coil springs used on the rest of the Land Rover model range. Logic- controlled by an electronic control unit, height sensors and driver controls, the system maintains front and rear self-levelling in the five height modes listed below. These notes show the versatility of the system and the purpose for which it was designed. However, for the casual driver, new to the vehicle, no prior knowledge or expertise is required; FAS will cycle automatically through appropriate modes according to prior programming. The driver need not even know EAS is fitted. On engine start-up EAS assumes the last selected ride height.

Electronic traction control - ETC. ETC is a standard/optional feature, available only on ABS-equipped Range Rovers. It inhibits wheel-spin by applying brake to a spinning rear wheel and thus enhances traction on ice, snow or in severe off-road conditions. It utilises ABS sensors for wheel speed determination and brakes the spinning wheel to, through the axle differential, apply torque to the stationary wheel. Like ABS. it is especially effective in maintaining control when one side of the vehicle is on a more slippery surface than the other - a so-called 'split-p surface. A dashboard light illuminates when the system is operating. The function is inhibited above 50 kph, a speed above which unintentional wheel spin is unlikely to occur..

Engine braking. Vehicle retardation derived from engaging a low gear and taking your foot off the throttle.

Emergency flotation (pressure). Very low tyre pressure (about 60% of normal road pressures), always associated with a low maximum permitted speed (20 kph or 12 mph) used for traversing or recovery from very soft ground. Such low pressures cause extreme tyre sidewall flexing - hence the speed limitation.

Emergency soft. Another name for emergency flotation tyre pressure - see above.

Fatigue life. Number of specified load reversals at which a metal component will fail. In the context of this book see fatigue life of nylon snatch-towing ropes -'Recovery - snatch-towing'.

Flat-top: A piston without a dish or dome, although it usually has valve reliefs machined into the top.

Flotation. Characteristic of a vehicle, by reason of large softly inflated tyres, not to sink on soft going such as mud or sand.

Four-wheel drive (4x4). Vehicle transmission system in which engine power is applied to all four wheels. The term 4x4 (four by four) has the specific connotation that it is a four (wheeled vehicle driven) by four (wheels).

Full-Floater: A rearend design in which the axles don’t carry the weight of the vehicle. This is the preferred setup for ’wheeling because if the axle breaks, the vehicle can still roll freely.

Fullsize: Usually the largest pickup truck a manufacturer makes for the public. The term has been used rather loosely in recent years as vehicles have become smaller. A Toyota T100 is called a fullsize even though many would argue it is not big enough.

Full-time 4x4. A transmission system on a four-wheeled vehicle in which all four wheels are driven by the engine all the time. (As opposed to a vehicle that is normally in two-wheel drive with four-wheel drive selected by a separate lever when required.)

Geometric limitations. A term coined for this book to describe the limitations and extent of approach and departure angles, ramp angle, steering lock, articulation and - an even newer term - longitudinal articulation angle.

Gnarly: (1) A trail that is extremely difficult. (2) Both a positive and a negative description (depending on the context) used by younger generations.

Go-Juice: Gasoline.

Granny Low: An ultralow First gear in a manual transmission, typically between 4.3:1 and 7.0:1. If Granny can pass you in her walker while you are in First gear, you have a granny-low First gear.

Grenade: To blow up a part on your truck. Trannies, rearends, transfer cases, and engines can grenade. This is definitely a bad thing.

Ground clearance. Space between the ground and a given mechanical part of the vehicle. Usually, when quoted for a vehicle, taken as the least for any component on the vehicle - the space under the differential casing. But note difference between under-axle and underbelly clearance.

Ground stress. Term coined for this book to indicate how much strength is being asked of a particular piece of ground in terms of flotation or lateral shear to accommodate traction, braking or acceleration.

Heavy Metal: Slang for a fullsize truck.

Heel and toe wear. Jargon for the uneven front to rear wear on individual blocks of a bold off-road tyre tread when used on roads.

High-centered: When a vehicle is caught on an obstacle near the center, usually on the frame, and is unable to move. This is more common with stock-height vehicles traveling over rough terrain.

High box. Status of the transmission when the two-speed transfer gearbox lever is in the high ratio position - for normal, on-road, day-to-day use.

High ratio. Term to describe the transmission when the transfer gearbox lever is in the high position - high box above.

Hi-lift jack. Versatile lever-operated mechanical bumper jack capable of a lift of a metre or more.

Hi-lo lever. Term sometimes used to describe the transfer gearbox lever. High Load suspension. An option on the Defender 90 enabling payload to be raised by about 150 kg.

Hummer: A vehicle made by AM General. It was originally produced for the military but is now available to civilians. The military uses the designation HMMWV (pronounced Hum-Vee), which stands for High Mobility Multiple Wheeled Vehicle.

Hydraulic D: A nasty occurrence in which the engine sucks water into the cylinders through the intake. Unfortunately, water doesn’t compress well, and the result is usually bent connecting rods and valves, which make the engine unable to turn.

Kerb weight. Unladen weight, ie empty vehicle plus full fuel plus 75 kg driver.

KERR. Kinetic Energy Recovery Rope. Descriptive term coined to describe specially specified nylon ropes capable of stretching during snatch tow.

GVW. Gross vehicle weight - the maximum permitted laden weight of a vehicle including payload, fuel and driver.

Kinetic energy. Energy of motion, proportional to the total weight of the vehicle and the square of its speed. Thus if a vehicle's weight doubles its KE also goes up two times; but if its speed doubles its KE increases by two squared, ie four times. See 'Recovery - snatch-towing'

Kiss: When a truck lightly hits an object such as a rock, but neither sustains damage, as in, Did you hit that rock? No, I just kissed it.”

Laden. Vehicle carrying some or full payload. See also GVW above concerning loading to maximum permitted weight.

Levelled suspension. A means of eliminating the 'squat' of the rear suspension under load by a hydraulic self-levelling unit between the chassis and the centre of the rear axle. Standard on coil sprung Range Rovers, Defender 110 Station Wagons and County; special order on any other Defender 110.

Lift Block: A block placed between the rear axle and leaf springs to gain lift. Lift blocks should never be used on front axles, and such use is illegal in most states.

Lifted: A truck that is raised by either a suspension or a body lift or both.

Line: The positioning and maneuvering of a truck over an obstacle. The line a driver takes can be the difference between success and stuck.

Locked In: Manual locking hubs set in the lock position are said to be locked in.

Locked Up: (1) A 4x4 that has locking differentials at both ends is locked up. (2) A hydraulic’d motor is usually locked up.

Locker: A differential that allows engine power to be delivered to both wheels, giving maximum traction. This is helpful during situations when one wheel is off the ground.

Longitudinal articulation coefficient (CLA) single number that conveys the off-road, 'twisty ground' potential of an off-road vehicle. A given max wheel movement enhances this capability more on a short wheelbase than on a long wheelbase vehicle. (CLA) is a non-dimensional parameter, provisionally coined, (higher values mean better articulation) that takes account of both wheel movement and wheelbase; it relates to the angle between the ground and a line joining the front and rear hubs (or tyre periphery) when one wheel is on full bump and the other fully

Low box. Status of the transmission when the transfer gearbox lever is in the low position - for difficult off-road conditions demanding greater traction or low speed control.

Low Gears: Gears with a numerically higher ratio; 4.56 gears are lower than 3.73 gears.

Low ratio. Term to describe the transmission when transfer gearbox lever is in the low position.

Massaged: (1) Modifications usually to an engine or body. (2) Sheetmetal damage that occurs from hitting rocks or other obstacles during four-wheeling.

Meats: Tires. Also referred to as donuts, treads, or rubber. Generally used when referring to oversized tires.

Mondo: Large, huge, or massive.

Marshalling. ('Marshaller' derived from ground-crew who marshal aircraft on airport aprons.) In the context of off-road operations, taken to mean the detailed direction of a vehicle by a marshaller outside the vehicle who is able to see all four wheels and also the difficult ground being traversed. Marshalling should be undertaken when there is the danger of damaging tyre sidewalls or the underside of the vehicle on rocks or other obstacles.

M+S tyres. Mud and snow tyres. A generic term for 4x4 tyres with a road-oriented, not especially bold, tread pattern suitable for mild snow and mud conditions.

Mud tyres. Bold, open-tread tyres optimised for mud with disadvantages on hard roads.

Multi-purpose tyre. Combination / compromise between on-road and mud tyres.

NATO towing hook. Large, robust, four-bolt attachment towing pintle with top-closure and, usually, 3600 rotational capability about the longitudinal axis originally specified for NATO 7.5 tonne military vehicles. Suitable for off-road towing albeit, due to the fact that a trailer towing eye will not be a close fit over the hook, it generates quite a bit of 'goods train' fore and aft banging.

Nose load. Trailers should be nose heavy; the nose-load is the amount of nose-heaviness (sometimes called trailer preponderance') measured at the tow-hitch and must be considered part of the towing vehicle's payload.

Off Camber: When the trail is on a sideways incline, usually very steep. Off-camber trails increase the likelihood of a rollover.

Off-Road: A misnomer for driving on established dirt trails. Unfortunately, in recent years this term has become politically incorrect because it implies leaving the trail and bounding through the countryside. The correct term is “off-highway,” but most people (including us) still use off-road to refer to driving on dirt roads.

On-foot recce. Inspecting a difficult off-road obstacle on foot before committing your vehicle to it.

Overrun brakes. Trailer brakes activated by the tendency of the trailer to overtake -or overrun - the towing vehicle when the vehicle brakes or slows down.

Over-torque. Used in this book to convey the concept of applying too much torque (or power) to the wheels so that they break their grip with the ground and spin.

Open Differential: A differential that usually comes stock on 4x4s. It directs power to the wheel with the least resistance to spinning. One-leggers and peg-leggers are slang terms for open diffs.

Paperweight: A part that is broken beyond repair.

Plumbing: Any hose on a vehicle, such as the brake lines.

PTO: Power Take-Off. An output shaft on the transfer case or transmission that sends engine power to accessories like a PTO winch. A PTO-driven accessory is not very common on noncommercial vehicles.

Pump Gas: 85- to 93-octane gas available at filling stations.

Pumpkin: The centersection of a front or rear differential housing. This can also refer to a removable centersection such as the kind used in a Ford 9-inch or a Toyota rear differential housing.

Radial ply tyre. A type of tyre construction in which sidewall structural plies run radially out towards the tread instead of criss-cross diagonally. With their thinner, more flexible sidewalls, radial tyres have lower rolling resistance than cross-ply tyres (yielding better fuel consumption) as well as giving longer tread life. They can accommodate the use of low inflation pressures without overheating, due to their flexible sidewalls, but are sometimes more prone to sidewall damage when operating in rocky or stony conditions. Because radial tyres invariably also have a braced tread area of great dimensional stability, they 'track-lay' the tread (like a bulldozer), do not suffer from 'tread shuffle' and so achieve more traction in limiting off-road conditions.

Ramp angle. A measure of vehicle under-belly clearance or the
ability to drive over a sharp ridge or ramp without touching the underside of the vehicle on the obstacle. The ramp angle is the angle measured from the lowest part of the chassis at mid-wheelbase down to the periphery of front and rear wheels. Obviously a short wheelbase vehicle with large wheels will have the smallest ramp angle and best under-belly clearance; a Defender 90 will be better than a Defender 130 in this respect.

Ramp breakover angle. The fuller title of 'Ramp angle' above.

Range change. Term sometimes used for the transfer gearbox lever.

Reduced inflation. Lowering tyre pressures to increase flotation in soft ground conditions such as mud or soft sand.

Rockcrawler: A 4x4 built specifically for maneuvering through rocky terrain.

Sand ladders. A pair of aluminium ladders, about 170 cm long, specially made with rungs closer than normal, to lay beneath the vehicle wheels in soft sand to give grip and flotation.

Sand tracks. Generic name sometimes given to any item fulfilling the role of a sand ladder. May be PSP (pierced steel planking).

Sand channels. Term often interchangeable with sand tracks, channels were used for this purpose. Can include articulated sand planks.

Sand tyres. Term often used to mean desert tyre - implying an ability to cope with desert rock and stones as well as sand. These tyres are characterised by tread blocks of a gentle, shouldered profile with no bold, right-angled edges such as a mud tyre would have. Radial construction is far more suited to the low inflation pressures sometimes used in sand. Despite their appearance, 'balloon' tyres with circumferential groove treads are considerably less effective in sand than a radial such as the Michelin XS.

Salt flat. Salt marsh of very unreliable consistency and bearing strength found in desert regions and characterised by a top crust of varying thickness and strength with soft salt mud of great depth beneath it.

Selectable four-wheel drive. A four-wheeled vehicle which proceeds normally in two-wheel drive but on which, by means of a lever control, four-wheel drive may be selected. It is important to remember that such vehicles in four-wheel drive do not have the benefit of a centre differential

Self centring. The characteristic of front (steered) wheels to resume the straight-ahead position due to castor angle (See 'Castor angle') when the steering wheel is released. This characteristic can be utilised to enhance safety when driving in deep wheel ruts on slippery ground.

Sidewall. The external 'walls' of a tyre between the tread and the bead or wheel rim. This area is particularly vulnerable on radial ply tyres to damage in off-road operations from oblique rubbing contact with side-swiping sharp rocks. Driver awareness essential.

Sidewall awareness. Awareness by sensitive drivers of the susceptibility to damage of the tyre sidewall. An attribute worth developing.

Sidewall deflection. Outward movement of the tyre sidewall in the region of the ground contact patch due to low inflation pressures or hitting a sharp bump with excess speed. It is important not to run tyres at less than recommended inflation pressures for given maximum speeds and loads since by doing so you will exceed the manufacturer's specified limits for sidewall deflection and thus cause overheating and serious damage to the tyre

Shock loading. In the context of this book, taken to mean the arrest of mechanical motion in an excessively abrupt way or the application of sharp load reversals in a such a way as to risk structural failure. For example, the application of the handbrake whilst the vehicle is in motion can cause unacceptable shock loading of the rear axle half-shafts. Engaging diff-lock whilst one or more wheel is spinning could also result in severe and damaging shock load to the transmission

Show Truck: A customized truck that is built specifically for competing in shows and for looks. These trucks rarely see use.

Small gear lever. Don't be embarrassed if you can't remember the name for the transfer gear lever..!

Snatch tow. A method of recovering a stuck vehicle in which the towing vehicle is in motion before taking up the slack in the tow rope. Use only using special-purpose stretch ropes and specified procedures for this,

Snatch Block: A winching device used to double-line or to change the winch’s direction of pull. It usually consists of a hook, or some other method of attaching the device to an anchor, and a pulley for the winch cable.

Steering lock. The extent to which the steering wheel may be moved to the right or left. Thus 'full lock' implies movement of the steering wheel as far as it will go right or left.

Stretch limit (KERR ropes). The extent to which a kinetic energy recovery rope will stretch before it is in danger of breaking. A gnide for the Marlow Ropes Recovaline is 40% stretch; this limit should NEVER be approached.

Sucking Sand: If you are following a vehicle on a dry dirt road with the windows open, you are sucking sand.

Swamped: (1) When a vehicle becomes stuck while submarining and fills with water. (2) An engine that has either stalled or hydraulic’d during a water crossing.

Taco D: A frame or other part such as an axle that has been severely bent, usually when the truck has been jumped too high.

Tag: To hit an obstacle with some part of the truck, as in “I tagged my bumper on that ledge.”

Tail Gunner: The last vehicle in a trail-ride caravan. The tail gunner is usually responsible for making sure everyone finishes the trail.

Tall Gears: Gears with a numerically lower ratio; 3.73:1 gears are taller than 4.56:1 gears.

T-Case: Short for transfer case. A device usually attached directly to the transmission. The transfer case is a gearbox that splits engine power to the front and rear axles. You can select two-wheel-drive or four-wheel-drive high or low range with most transfer cases.

Thrased: When something has been used far beyond its limit. For example, when a truck has been beaten with wreckless abandon on a trail it had no business being on in the first place, it is said to have been thrashed.

Three-Wheeling: A term used to describe when one tire has left the ground while wheeling. For example, if the driver-side front tire drops into a large enough hole, the passenger-side rear tire will lift off the ground.

Todius: A term our colleagues at 4-Wheel & Off-Road dreamed up, and we intend to use it shamelessly. It means huge, massive, or enlarged. For example, 44-inch Mudders are todious meats.

Trail Boss: The trail leader on a trail ride.

Trailer Queen: Something you will not see in this magazine. It’s a 4x4 that pretends to be trail-ready, but it’s really just a show truck carted around on a trailer.

Tranny: Short for transmission.

Traction. In the context of this book the concept of achieving grip between the wheels and the ground without slip, skid or sinkage.

Traction Control. See 'Electronic Traction Control, ETC'.

Traction controls. Here taken to mean the lever controlling the transfer gearbox and centre differential lock.

Tractive effort. The amount of 'pull' exerted by a vehicle as a result of traction.

Trailer preponderance. Sometimes used to denote down-load on the vehicle towing hitch.

Transfer box. Originally the name implied the transfer of power from the main gearbox to the front axle as well as the rear axle on a four-wheel drive vehicle. In all Land Rover products a two-speed transfer box is fitted so it has the additional role of permitting power from the gearbox to go to the axles at normal 1:1 gearing (high ratio) or geared down by nearly 2:1 (low ratio).

Transfer Gear Lever. The small gear lever in the cab next to the main gear lever. It controls whether the transmission is in 'high ratio' or 'low ratio' in the transfer box. The same lever also controls the engagement of the diff lock - see above -except in the Range Rover where a viscous coupling fulfils this requirement automatically.

Transmission brake. The handbrake on all Land Rovers operates by gripping the rear propeller shaft at the point where it leaves the transfer gearbox and is thus called a transmission brake. It should be used as a parking brake only and should never be operated whilst the vehicle is in motion except in emergency -

Transmission wind-up. Read first 'Centre differential',. A 4x4 with no centre differential or one driven with the centre diff locked (ie in both cases the front and rear propeller shafts locked together) is unable to accommodate the small differences in distance normally travelled by the front wheels compared to the rear wheels. The diff-lock ensures both propeller shafts rotate exactly the same amount despite the small differences in distance actually travelled. This results in some wheel slip and skid which, on loose ground, can take place without any harm. On hard roads, however, the superior wheel grip makes it difficult for the wheels to slip much and in the process of trying to do so considerable torsional stress builds up in the transmission. This is known as transmission wind-up and can sometimes exert so much stress that the diff-lock gears will not disengage when so selected. You will also sense very heavy steering. If this occurs due to your forgetting to de-select diff-lock on hard ground (or at any other time) and the diff lock will not disengage, the solution is to reverse the vehicle some distance until the diff-lock warning light extinguishes.

Tree-Hugger: Derogatory term for an extreme environmentalist; not to be confused with Tree-Saver (see below).

Tree-Saver: A nylon strap designed to go around a tree to protect it while it’s being used as an anchor point for winching. This is much better than wrapping the cable around the tree, which ruins the cable and the tree.

Tweak: (1) Modifying something to enhance performance, usually called tweaking. (2) To incur body or component damage, as in “I tweaked my bumper when I hit that rock.”

Unladen. Vehicle carrying fuel, driver but no payload or other load - see 'Kerb' above.

Viscous coupling unit (VCU). A unit fitted as standard to all Range Rovers across the centre differential (not instead of it) automatically to effect locking of the differential when a significant speed difference between front and rear propeller shafts is sensed. Conceptually it comprises a cylinder attached to the rear prop shaft into which an extension of the front prop shaft is introduced. Discs are attached alternately to the front prop shaft and the inside of the cylinder so that they interleave very closely within the cylinder. The cylinder is sealed at both ends and is filled with a special silicone fluid which has the characteristic of markedly increasing its viscosity when stirred. Thus when one prop shaft rotates relative to the other one - the situation of front (or rear) axle wheel-spin - the fluid increases its viscosity enough to lock the shafts together. When relative rotation ceases the viscosity changes back to its original value and the shafts are unlocked. The viscous coupling unit (VCU) has the advantage of being automatic on both engagement and disengagement and its action is gradual and without shock-loading to the transmission.

Wading plugs. Oil drain holes are provided in the bottom of the clutch housing (and the camshaft drive-belt housing on Tdi and 2.5D engines) to preclude the possibility of the clutch or cam belts becoming contaminated in the event of oil leaks from the adjacent bearings. Wading plugs should be fitted to block these holes when driving through water over 30 cm deep and subsequently removed.

Wheel Travel: The total distance a wheel can travel up and down. As a general rule, the more wheel travel, the better.

Yank Strap: A large nylon strap used for pulling out stuck vehicles. Also referred to as a tow strap.








Article Sources:
Four Wheeler. 4x4 Dictionary. 2011. http://www.fourwheeler.com/techarticles/71038_4x4_dictionary_terms/index.html and Wood Park Off-Road. Off-Road 4×4 Glossary. 2011. http://www.woodpark-offroad.comhttp//www.woodpark-offroad.com/off-road-4x4_glossary.php