4x4 Tyres Limited is a specialist 4x4 Alloy Wheel, Tyre & Accessories supplier with over 40 years experience, supplying both retail and wholesale clients including : Ministry of Defence & other Major Blue Chip companies.
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About 4x4's:
Four-wheel drive, 4WD, 4x4 ("four by four"), or AWD ("all wheel drive") is a four-wheeled vehicle with a drivetrain that allows all four wheels to receive torque from the engine simultaneously. While many people associate the term with off-road vehicles, powering all four wheels provides better control in normal road cars on many surfaces, and is an important part of rally racing.
In abbreviations such as 4x4, the first figure is the number of wheels; the second is the number of powered wheels. 4x2 means a four-wheel vehicle in which engine power is transmitted to only two wheels: the front two in front-wheel drive or the rear two in rear-wheel drive[1].
There is often confusion as to the difference between 4x4s and Sport Utility Vehicles. This leads to criticisms of 4x4 vehicles in the media that should actually be directed at Sport Utility Vehicles (see criticism of sport utility vehicles).
The term four-wheel drive describes truck-like vehicles that may allow the driver to manually switch (or automatically if fitted) between two-wheel drive mode (if available) for streets and four-wheel drive mode for low traction conditions such as ice, mud, snow, slippery surfaces, or loose gravel.[2]
All-wheel drive (AWD) is often used to describe a "full time" 4WD that may be used on dry pavement without destroying the drivetrain, although the term may be abused when marketing a vehicle.[3] AWD can be used on dry pavement because it employs a center differential, which allows each tire to rotate at a different speed. ("Full-Time" 4WD can be disengaged and the center differential can be locked, essentially turning it into regular 4WD. On the other hand, AWD cannot be disengaged and the center differential cannot be locked.[4][5]) 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.
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. Audi's quattro, Mercedes-Benz's 4Matic, BMW with the xDrive, and Volkswagen's 4motion, for example, can mean either an automatically-engaging "on-demand" system with a Haldex Traction clutch, or a continuously-operating permanent 4WD system with a Torsen (torque-sensing) differential.
When powering two wheels simultaneously the wheels must be allowed to rotate at different speeds as the vehicle goes around curves. The problem is even more complicated when driving all four wheels. 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 independently 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. Once it does slip, however, recovery is difficult. If the left front wheel of a 4WD vehicle slips on an icy patch of road, for instance, the slipping wheel will spin faster than the other wheels due to the lower traction at that wheel. Although the amount of torque applied to each wheel will be identical, the amount of traction at each driven wheel will be limited to that of the wheel with the least traction (at least one wheel on ice in this case). This problem can happen in both 2WD and 4WD vehicles, whenever a driven wheel is placed on a surface with little traction or raised off the ground. The simplistic design works acceptably well for 2WD vehicles. It is much less acceptable for 4WD vehicles because 4WD vehicles have twice as many wheels to lose traction, increasing the likelihood that it will happen. 4WD vehicles may also be more likely to be driven on surfaces with reduced traction.
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