Four wheel drive, 4WD, or 4x4 ("four by four") is a four-wheeled vehicle with a drivetrain that allows all four wheels to receive power from the engine simultaneously. In the United States, these cars are included in the broader sport utility vehicle category. While many people associate the term with off-road vehicles, powering all four wheels provides better control on many surfaces, and is an important part of rally racing.
The term four-wheel drive describes truck-like vehicles that require the driver to manually switch between two-wheel drive mode for streets and four-wheel drive mode for low traction conditions such as ice, mud, snow, slippery surfaces, or loose gravel. All-wheel drive (AWD) is often used to describe a "full time" 4WD that may be used on dry pavement without destroying the drivetrain (It should be noted that "Full-Time" 4WD can be disengaged, and the center differential can be locked; essentially turning it into regular 4WD. Whereas AWD cannot be disengaged and the center differential cannot be locked.) , although the term may be abused when marketing a vehicle. AWD can be used on dry pavement because it employs the use of a center differential, which allows each tire to receive different amounts of power. This eliminates driveline binding, wheel hop and other driveline issues associated with the use of 4WD on dry pavement. With vehicles with more than four wheels, AWD means all wheels drive the vehicle, to varying degrees of engagement while 4WD means only four of the wheels drive the vehicle continuously. AWD can also be thought of as automatic 4WD, having the car engage all four wheels when conditions warrant and disengage without notifying the driver or occupants about the status of the drivetrain. This shouldn't be confused with the term automatic transmission.
Identical drivetrain systems are commonly marketed under different names for upmarket and downmarket branding, and conversely different drivetrain systems are commonly marketed under the same name for brand uniformity. For example, Audi's Quattro, DaimlerChrysler's 4MATIC used on Mercedes-Benz products, BMW with the xDrive, and Volkswagen's 4motion can mean either an automatically-engaging system with a Haldex clutch or a continuously-operating system with a Torsen differential.
There is often confusion as to the difference between 4X4s and SUVs. This leads to criticisms of 4X4 vehicles in the media that should actually be directed at SUVs (see SUV Criticism).
When powering two wheels simultaneously, the wheels must be allowed to rotate at different speeds as the vehicle goes around curves. When driving all four wheels, the problem is even more complicated. A design that fails to account for this will cause the vehicle to handle poorly on turns, fighting the driver as the tires slip and skid from the mismatched speeds.
A differential allows one input shaft to drive two output shafts with different speeds. The differential distributes torque (angular force) evenly, while distributing angular velocity (turning speed) such that the average for the two output shafts is equal to that of the input shaft. Each powered axle requires a differential to distribute power between the left and the right sides. When all four wheels are driven, a third differential can be used to distribute power between the front and the rear axles.
Such a design handles well. It distributes power evenly and smoothly, and makes slippage unlikely. However, once it does slip, recovery is difficult. Suppose that the left front wheel slips on an icy patch of road with a design that drives all four wheels. The slipping wheel will receive all of the power, causing it to spin twice as fast as desired, while the wheel on the other side stops moving. The average speed remains unchanged, and neither wheel gets any torque. A similar problem occurs between the front and rear axles via the center differential. The front left wheel receives all of the power, again doubling its speed while the rear wheels stop moving; again, the average speed is maintained. The available torque goes to zero, and the left front wheel actually turns four times as fast as it should be turning, preventing the other three wheels from turning. This problem can happen in both 2WD and 4WD vehicles, whenever a driven wheel is placed on a patch of slick ice or raised off the ground. The simplistic design works acceptably well for 2WD vehicles, but since 4WD vehicles are more likely to have a driven wheel on an icy patch, the differential design is less acceptable.
Traction control was invented to solve this problem for 2WD vehicles. When one wheel spins out of control, the brake is automatically applied to that wheel. By preventing one wheel from spinning freely, power is divided between the pavement for the non-slipping wheel and the brake for the slipping wheel. This is an effective solution, although it causes additional brake wear and may cause a sudden jolt that impacts handling. By extending traction control to act on all four wheels, the simple three-differential 4WD design will see limited wheel spin. This design is commonly seen on luxury crossover SUVs.
Locking differentials temporarily lock together a differential's output shafts, causing all wheels to turn at the same rate, providing torque in case of slippage. This is generally used for the center differential, which distributes power between the front and the rear axles. While a drivetrain that turns all wheels equally would normally fight the driver and cause handling problems, this is not a concern when wheels are slipping.
The two most common locking differentials use either a computer-controlled multi-plate clutch or viscous coupling unit to join the shafts, while older differentials generally used manually operated locking devices. In the multi-plate clutch, the vehicle's computer senses slippage and locks the shafts, causing a small jolt when it activates, which can disturb the driver or cause additional traction loss. In the viscous coupling differentials, the shear stress of high shaft speed differences causes a dilatant fluid in the differential to become solid, linking the two shafts. This design suffers from fluid degradation with age and from exponential locking behavior. Some designs use gearing to create a small rotational difference, which hastens torque transfer.
A third approach to limiting slippage is the Torsen differential. A Torsen differential allows the output shafts to receive different amounts of torque. This design does not provide for traction when one wheel is spinning freely, where there is no torque, it provides excellent handling in less extreme situations. A typical Torsen II differential can deliver up to twice as much torque to the high traction side before traction is exceeded at the lower tractive side.
Finally, many lower-cost vehicles entirely eliminate the center differential. These vehicles behave as 2WD vehicles under normal conditions. When the drive wheels begin to slip, one of the locking mechanisms discussed above will join the front and rear axles. Such systems distribute power unevenly under normal conditions, and thus do not help prevent the loss of traction, instead only enabling recovery once traction is lost. Most minivan 4WD/AWD systems are of this type, usually with the front wheels powered during normal driving conditions and the rear wheels served via a viscous coupling unit. Such systems may be described as having a 95/5 or 90/10 power split.
The true inventor of four-wheel drive is not really known; the history of such was not well recorded. Ferdinand Porsche designed and built a four-wheel driven Electric vehicle for the k. u. k. Hofwagenfabrik Ludwig Lohner & Co. (at Vienna) in 1899, presented to the public during the 1900 World Exhibition at Paris. The vehicle was powered by an electric hub at each wheel, a design later used by NASA in the Lunar rover. Although clumsily heavy, the vehicle proved a powerful sprinter and record-breaker in the hands of its owner E.W. Hart. Due to its unusual status the so-called Lohner-Porsche is not widely credited as the first four-wheel driven automobile.
The first ever four-wheel drive car (as well as hill-climb racer) with combustion engine, the Spyker 60 H.P., was presented in 1903 by Dutch brothers Jacobus and Hendrik-Jan Spijker of Amsterdam. The two seater sports car, which was also the first ever car equipped with a six-cylinder engine and featured, as another novelty, brakes for all four wheels, is nowadays exhibit of the Louwman Collection (the former Nationaal Automobiel Museum) at Raamsdonksveer in The Netherlands.
Designs for four-wheel drive in the U.S., came from the Twyford Company of Brookville, PA in 1905, six were made there around 1906; one still exists and is displayed annually. The second U.S. four-wheel drive vehicle was built in 1908 by (what became) the Four Wheel Drive Auto Company (FWD) of Wisconsin. FWD would later produce over 20,000 of its four-wheel drive Model B trucks for the British and American armies during World War I.
Daimler-Benz also has a history in four-wheel drive. In 1907 the Daimler Motoren Gesellschaft had built a four-wheel driven vehicle called Dernburg-Wagen, also equipped with four-wheel steering, that was used by German colonial civil servant, Bernhard Dernburg, in Namibia. Mercedes and BMW, in 1926, introduced a rather sophisticated four-wheel drive, the G1, the G4 and G4 following. The 1937 Mercedes-Benz G5 and BMW 325 4x4 featured full time four-wheel drive, four-wheel steering, three differential lockers, and fully independent suspension. They were produced because of a government demand for a four-wheel drive passenger vehicle. The modern G-series/Wolf such as the G500 and G55 AMG still feature some of the attributes, with the exception of fully independent suspension since it hinders suspension articulation. The Unimog is another Mercedes truck.
It was not until "go-anywhere" vehicles were needed for the military that four-wheel drive found its place. The Jeep, originally developed by American Bantam but mass-produced by Willys and Ford, became the best-known four-wheel drive vehicle in the world during World War II. Willys (since 1950 owner of the Jeep name) introduced the CJ-2A in 1945 as the first full-production four-wheel drive passenger vehicle. Possibly beaten by the 1941 GAZ-61.
It was in 1948 that the Land Rover appeared at the Amsterdam Motor Show, originally conceived as a stop-gap product for the struggling Rover car company, and despite chronic under-investment succeeded far better than the passenger cars. Land Rover developed a luxury 4WD with the Range Rover in the 1970s, which unlike some offerings from other manufacturers, was capable of serious off-road use. The inspiration was from a Willys MB that was frequently offroaded on the farm belonging to chief engineer Maurice Wilks, and was felt that it needed some refinement.
Kaiser Jeep introduced a 4WD wagon called the Wagoneer in 1963. It was revolutionary at the time, not only because of its technical innovations such as an independent front suspension and the first automatic transmission with 4WD, but also because it was equipped and finished as a regular passenger automobile. The Super Wagoneer (1966 to 1969) was powered by Rambler or Buick V8s. Its high level of equipment made it the first "luxury" SUV. American Motors (AMC) acquired Kaiser's Jeep Division in 1970 and quickly upgraded and expanded the entire line of serious off-road built 4WD vehicles. The top range full-size Wagoneer Limited continued to compete with traditional luxury cars. It was relatively unchanged during its production, even after Chrysler's buyout of AMC, all the way through 1991.
Jensen applied the Formula Ferguson four-wheel drive system to their 1966 Jensen FF marking the first time 4WD was used in a production sports car. However, with a total of 320 build units this did not sell in appreciable numbers. The first manufacturer to develop four-wheel drive for road-going cars was Subaru, who introduced the mass-produced 4WD Leone in 1972. This model eventually became the best-selling 4WD car in the world. Subaru's success in marketing AWD vehicles has led to an AWD-only lineup in almost all of its markets outside of Japan. By 1998, Subaru discontinued all two-wheel drive vehicles in North America, where it remains the only brand to be exclusively AWD.
American Motors introduced the innovative Eagle for the 1980 model year. This was the world's first complete line (sedan, coupe, and station wagon) of permanent automatic all-wheel drive passenger models. The new Eagles combined Jeep technology with an existing and proven AMC passenger automobile platform. They ushered a whole new product category of "sport-utility" or Crossover SUV. AMC's Eagles came with the comfort and high level appointments expected of regular passenger models and used the off-road technology for an extra margin of safety and traction.
The Eagle's thick viscous fluid central differential provided quiet and smooth transfer of power that was directed proportionally to the axle with the greatest traction. This was a true full-time system operating only in four-wheel drive without undue wear on suspension or driveline components. There was no low range in the transfer case. This became the forerunner of the designs that followed from other manufacturers. The automobile press at the time tested the traction of the Eagles and described it as far superior to the Subaru's and that it could beat many so-called off-road vehicles. Four Wheeler magazine concluded that the AMC Eagle was "The beginning of a new generation of cars."
The Eagles were popular (particularly in the snowbelt), had towing capacity, and came in several equipment levels including sport and luxury trims. Two additional models were added in 1981, the sub-compact SX/4 and Kammback. A manual transmission and a front axle-disconnect feature were also made available for greater fuel economy. During 1981 and 1982 a unique convertible was added to the line. The Eagle's monocoque body was reinforced for the conversion and had a steel targa bar with a removable fiberglass roof section.
The Eagle station wagon remained in production for one year after Chrysler Corporation acquired AMC in 1987.
Audi also introduced a permanently all-wheel driven road-going car, the Audi Quattro, in 1980. Audi's chassis engineer, Jorg Bensinger, had noticed in winter tests in Scandinavia that a vehicle used by the German Army, the Volkswagen Iltis, could beat any high performance Audi. He proposed developing a four-wheel drive car, soon used for rallying to improve Audi's conservative image, the resulting rally bred Audi Quattro was a famous and historically significant Rally car. This feature was also extended to Audi's production cars and is still available.
In 1987, Toyota also developed a car built for competition in rally campaigns. A limited number of road-going FIA Homologation Special Vehicle Celica GT-Fours (otherwise known as Toyota Celica Turbo All-Trac in some markets) were produced. The All-Trac system was later available on serial production Toyota Camry, Toyota Corolla, and Toyota Previa models.
Some of the earliest mid-engined four-wheel drive cars were the various road-legal rally cars made for Group B homologation, such as the Ford RS200 made from 1984-86. In 1989, niche maker Panther Westwinds created a mid-engined four-wheel drive, the Panther Solo 2.
4WD in road racing
Bugatti created a total of three four-wheel drive racers, the Type 53, in 1932, but the cars were legendary for having poor handling. Ferguson Research Ltd. built the front-engined P99 Formula One car that actually won a non-WC race with Stirling Moss in 1961. In 1969, Team Lotus raced cars in F1 and the Indy 500 that had both turbine-engines and 4WD, as well as the 4WD-Lotus 63 that had the standard Cosworth engine. Matra also raced a similar MS84, while Team McLaren tested its design only. All these F1 cars were considered inferior to their RWD counterparts and the idea was discontinued, even though Lotus tried repeatedly.
Although in the strictest sense, the term "four-wheel drive" refers to a capability that a vehicle may have, it is also used to denote the entire vehicle itself. In Australia, vehicles without significant offroad capabilities are often referred to as All-Wheel Drives (AWD) or SUVs, while those with offroad capabilities are referred to as "four-wheel drives". This term is sometimes also used in North America, somewhat interchangeably for SUVs and pickup trucks and is sometimes erroneously applied to two-wheel-drive variants of these vehicles.
The term 4x4 (read either four by four or four times four) is used to denote the total number of wheels on a vehicle and the number of driven wheels; it is often applied to vehicles equipped with either full-time or part-time four-wheel-drive. The term 4x4 is common in North America and is generally used when marketing a new or used vehicle, and is sometimes applied as badging on a vehicle equipped with four-wheel drive. Similarly, a 4x2 would be appropriate for most two-wheel-drive vehicles, although this is rarely used in the USA in practice. In Australia the term is often used to describe a pickup truck that sits very high on its suspension. This is to avoid the confusion that the vehicle might be a 4x4 because it appears to be otherwise suited to off-road applications.
Large American trucks with dual tires on the rear axles (also called duallys or duallies) and two driven axles are officially badged as 4x4s, despite having six driven wheels because the 'dual' wheels behave as a single wheel for traction purposes and are not individually powered. True 6x6 vehicles with three powered axles such as the famous "deuce and a half" truck used by the U.S. Army has three axles (two rear, one front), all of them driven. This vehicle is a true 6x6, as is the Pinzgauer, which is popular with defense forces around the globe.
Another related term is 4-wheeler (or four-wheeler). This generally refers to all-terrain vehicles with four wheels and does not indicate the number of driven wheels; a "four wheeler" may have two or four-wheel drive.
Unusual four-wheel drive systems
Prompted by a perceived need for a simple, inexpensive all-terrain vehicle for oil exploration in North Africa, the French motor manufacturer Citroën developed the 2CV Sahara. Unlike other 4x4 vehicles which use a conventional transfer case to drive the front and rear axle, the Sahara had two engines, each independently driving a separate axle, with the rear engine facing backwards. The two throttles, clutches and gearchange mechanisms could be linked, so both 12 bhp 425 cc engines could run together, or they could be split and the car driven solely by either engine. Combined with twin fuel tanks and twin batteries (which could be set up to run either or both engines), the redundancy of two separate drive trains meant that they could make it back to civilization even after major mechanical failures. Only around 700 of these cars were built, and only 27 are known to exist today. Enthusiasts have built their own "new" Saharas, by rebuilding a 2CV and fitting the modified engine, gearbox and axle onto a new, strengthened chassis.
Suzuki Motors introduced the Suzuki Escudo Pikes Peak Edition in 1996. Though actual numbers were never released, this twin-engined vehicle is believed to weigh around 1760 pounds and produce nearly 1000bhp. The engine is a twin-turbo charged 2.0L V6 mated to a sequential 6-speed manual transmission.
Nissan Motors has developed a system called E4WD wherein the rear wheels in a car that is normally front-wheel drive are driven by electric motors. This system was introduced in some variants of the Nissan Cube and Tiida.
Most recently, DaimlerChrysler's Jeep Division debuted the twin engine, 670 hp Jeep Hurricane concept at the 2005 North American International Auto Show in Detroit. This vehicle has a unique "crab crawl" capability, which allows it to rotate in 360 degrees in place. It also has dual Hemi V8s.
4WD and AWD systems by design type
NOTE! Subaru's "Symmetrical AWD" system is actually 4 different systems based on drivetrain choice, see below.
Center differential with mechanical lock, or other torque transfer features
- Ford - Escort and Sierra Cosworth, Sierra and Granada 4x4 models
- H1 & HMMWV NVG 242HD AMG open center differential, locked center differential, Neutral, low range locked. Also Torsen1 differential at the front and rear axle, The H1 moved to Torsen2 when ABS was added. The H1 Alpha had optional locking differentials in place of torsens
- Land Rover Defender
- Range Rover
- Land Rover/Land Rover Discovery/LR3
- Hummer H2, H3 40/60 planetary with lock
- Lada Niva - full-time 4WD using worm gear limited-slip center differential
- Subaru Basic manual transmissions have a 50/50 center differential with viscous clutch, performance models have a planetary differential with computer regulated lockup. Automatic transmission models have ~45/55 planetary with computer controlled lock up
- Mercedes-Benz G-Class (locking center and lockers on both front- and rearaxle)
- Mercedes GL-Class
- Jeep Grand Cherokee, Commander (Quadra-Drive 2 version only for both vehicles)
- Jeep Liberty (Select-Trac) NVG 242 transfer case-rear drive, open center differential, locked center differential, Neutral, low range & locked
- Porsche Cayenne (Porsche Traction Management) 38/62 planetary with lockup clutch pack
- Volkswagen Touareg -double pinion 50/50 with lockup clutch pack
- Suzuki Grand Vitara -full-time 4WD using limited-slip center differential, off-road 4WD with selectable center differential lock and low range transfer case, traction control and electronic stability control
- Toyota Land Cruiser
- Toyota Sequoia (Multi-mode)
- Lexus RX350 -viscous coupling on center differential
- Lexus LX470 -open with lock
- Mercedes-Benz Unimog (locking center and rear with up to 10 low range gears).
- Mitsubishi Pajero (also known as Montero or Shogun)
- Nissan Pathfinder/Armada (All-Mode) multi clutch based with locking center differential
Note of the above vehicles all have a low range transfer case except some Subaru models.
Torsen Center diff
- Audi A4, A6, A8, S4, S6, S8, R8, Q7 (center) (quattro)
- Bentley Continental GT, Flying Spur Torsen1
- Chevrolet Trailblazer SS (center)(limited slip rear) Torsen3
- Lexus GX470 (center)(limited slip rear) Torsen3 with lock
- Toyota HiLux Surf or 4Runner (center) (also locking rear) Torsen3 with lock
- Toyota FJ cruiser (center) (only manual models) (also locking rear) Torsen3 with lock
- Volkswagen Phaeton (center)
Center diff no locking
- Cadillac Escalade, STS AWD, SRX AWD (The first two generations had a viscous clutch on the center differential)
- Chrysler 300C AWD
- Dodge Magnum, Charger AWD
- GMC Yukon Denali, XL Denali, Sierra Denali
- Mercedes 4MATIC cars, R class, and ML class (note some MLs had low range)
The above systems function by selectively using the tracton control system (via ABS) to brake a slipping wheel.
Multiple Clutch systems
- Acura MDX SH-AWD & VTM4
- Acura RL, RDX (SH-AWD) Right and left axleshaft
- Honda Pilot
- Honda Ridgeline
- Mitsubishi GTO MR/3000GT VR-4
- Mitsubishi Lancer Evolution Series
- Nissan A31 Cefiro SE4 (ATTESA E-TS)
- Nissan Skyline GT-R (ATTESA E-TS and ATTESSA E-TS-PRO) front axle coupling, rear differential locking
- Nissan Skyline GTS4 (ATTESA E-TS)
- Porsche 959 PSK front axle coupling, rear differential locking.
Clutch pack coupling
- Audi A3, TT (also Haldex)
- BMW 3series, 5series, X3, X5 (the initial X5's had a 38/62 planetary center differential)
- Chevrolet Equinox (GMPCA)
- Chrysler Pacifica (BorgWarner ITM3e) (on 2007 model)
- Dodge Caliber
- Dodge Nitro (Quadra-Trac 1)
- Jeep Grand Cherokee & SRT8 NVG 249, 247
- Ford Escape, Freestyle, Edge, Fusion, Five Hundred (Freestyle, FiveHundred Haldex based)(Escape Control Trac II, based)
- Jeep Compass (Freedom Drive)
- Honda CR-V, Element
- Infiniti G35x, M35x
- Lamborgini AWD variants VT series (viscous traction)
- Land Rover LR2 (also Haldex)
- Lincoln MKS, MKZ
- Mazdaspeed6 (a power takeoff unit linked to clutchpack with torque sensitive rear differential.)
- Mazda Tribute, CX-7, CX-9 (tribute Control Trac II, based)
- Mercury Milan, Montego, Mariner (Montego Haldex based)
- Mitsubishi Outlander (current generation)
- Nissan Murano automatic with manual lockup swithch
- Pontiac Torrent (GMPCA)
- Porsche 911 Awd variants (a version of BorgWarner ITM3e) -excluding the 964 series Porsche 911 carrera4 31/69 planetary center differential
- Subaru Legacy, Outback, Impreza, Forrester, Tribeca automatic transmission models: mechanical front drive, clutch coupled rear axle.
- Subaru low powered automatic transmission models
- Suzuki SX4, XL7, Aerio
- Toyota Rav4 (latest model, not older generations)
- Volkswagen Haldex based cars
- Volvo S40, S60, S80, V50, V70, XC70, XC90 (all Haldex based)
Note the above all function like 2wd when clutch pack not engaged, and like 4wd highrange in a part time 4wd system when the clutch is engaged (usually by computer although some allow manual control). Some in this category have varying degrees of control in the torque distribution between front and rear via allowing some of the clutches in a clutch pack to engage and slip varying amounts. An example of a system like this is the BorgWarner i-Trac(TM) system. Note the Haldex based car list was created from the list on Haldex corporate web site: | Haldex Cars. Interestingly a version of the BorgWarner ITM3e system is used on 2006 and up Porsche 911TT's. These Borg Warner systems were for runner of the popular Volkswagen DSG gearbox.
Off Road Drive (no center diff) (aka part time 4wd)
- Chevrolet Tahoe Z71, Suburban Z71, Silverado Z71, Colorado Z71
- Chevrolet Trailblazer and GMC Envoy
- Dodge Nitro (Quadra-Trac 2)
- Dodge Powerwagon (a ram version with front and rear lockers)
- Dodge Ram, Dakota
- Ford F series FX4, Explorer, Expedition, Sport Trac (all control trac 1)
- Ford Ranger (torsen rear diff)
- GMC Yukon Z71, Sierra Z71
- Infiniti QX56 (All-mode 4wd) Autoengages 4wd with slip
- Isuzu i-series
- Jeep Cherokee (Quadra-Trac 2)
- Jeep Liberty (Comand-Trac)
- Jeep Wrangler (Rubicon has a locking front as well as rear)
- Lincoln Mark LT
- Lincoln Navigator (Has slip sensing which can auto place into 4hi)
- Mazda B-series
- Mitsubishi Raider
- Nissan Armada, Pathfinder (All-mode 4wd) Autoengages 4wd with slip
- Nissan Titan, Xterra, Frontier (rear locker an option)
- Subaru Loyale, GL/DL, Brat Front/4wd/4wd lo, Justy
- Toyota FJ cruiser (auto trans models), Tacoma
- Toyota Tundra TRD
Note Off Road Drive systems may not be driven in 4wd mode on dry pavement as damage to the transfer case will occur
Drivetrain capability Table by type
|Drive train type||Dry road||On road light snow and rain with dry spots||Deep Snow||Off road capable|
|Rear Wheel Drive||Yes||Not well||Not well||No|
|Front Wheel Drive||Yes||Yes||Not well||No|
|Part-time 4WD||Only in RWD mode||Only in RWD mode||Yes||Yes|
Note!: For above table: AWD has no low range, Part-Time 4wd has no center diff but has low range, Full-time 4wd has a center diff and low range. Also note that ground clearance and breakover angles can play a large role in deep snow. Note the above table assumes locking, torsen, or limited slip differential in center and rear where applicable. Alternatively, brake-based traction control systems may be utilized in AWD or 4wd. Source info derived from: http://www.4x4abc.com
Note the reason that part time 4wd can not be used in dry conditions or where there are large dry areas with ice is the fact that under dry conditions when accelerating, decelerating, or turning the speed of the wheels will vary from side to side and front to rear. Because part-time 4wd has no center differential it forces the front and rear wheels to turn at the same speed even on dry tarmac. This causes tremendous stress to both the transfer case and the drive train. This paragraph based on info from http://www.4x4abc.com/4WD101/def_turnpart.html.
Common 4wd clearance dimensions
|Vehicle Name||Ground Clearance (in)||Approach Angle||Departure Angle||Ramp Over Angle|
|Land Rover Defender||9||51°||48°||?|
|Mitsubishi Pajero R||8.8||36.7°||34.8°||25.2°|
|Jeep Wrangler Rubicon||10.2||44.3°||40.4°||25.3°|
|Jeep Wrangler Rubicon UL||10.1||44.4°||40.5°||20.8°|
|Jeep Grand Cherokee||8.3||34.1°||27°||20°|
|Toyota FJ Cruiser||9.6||34°||30°||27.4°|
|Toyota HiLux Surf or 4Runner||9.1||30°||26°||??|
|Toyota Tacoma (TRD4x4)||9.4||35°||26°||21°|
|Land Rover Discover series3||12.4||37.2°||29.6°||27.9°|
|VW Touareg||6.3 to 11.8||33°||33°||27°|
|Mercedes GL class||7.9 to 10.9||33°||27°||°|
|Ford Expedition EL||8.7||24.1°||20.9°||18.7°|
|Subaru Outback 2.5xt||8.7 no typo||19°||23°||21°|
|Mercedes Unimog 132in||17||27° (bumper dependent)||47°||38°|
(Table information was derived from the maximum values as reported by manufacturer. Trim options and age may change actual values per vehicle)
- Category:All wheel drive vehicles
- Limited slip differential
- Off-road vehicle
- Sport utility vehicle
- Dune bashing
- Rock crawling
- Jeep four wheel drive systems
- Christini AWD Motorcycle - Quick Ride - by MotorcycleUSA.com
- Great Lakes 4x4 Interaction Forum
- 4x4 Off Road SUV - All about it
- All about 4WD, 4x4 and SUVs - tips, reviews and huge off-road community
|FF | FMR | FR | MF | RMR | RR | F4|
|Front-engine | Mid-engine | Rear-engine|
|Front-wheel drive | Rear-wheel drive | Four-wheel drive | Six-wheel drive|
- according to Car and Driver Vol52No8 Feb 07 page 110