The automobile or drivetrain layout describes where on the vehicle the engine and drive wheels are found. There are many different combinations of engine location and driven wheels -factors influencing the design choice include cost, complexity, reliability, packaging (location and size of the passenger compartment and boot), weight distribution, and the vehicle’s intended handling characteristics.
Layouts can roughly be divided into two categories: front- or rear-wheel drive. Four-wheel-drive vehicles may take on the characteristics of either, depending on how power is distributed to the wheels.
Most cars these days are front-wheel driven – cheaper layout, safest and lightest with the best interior space. Rear-wheel driven cars will provide higher sporting performance, usually found only in higher powered cars, and good for fast laps or powersliding. With modern vehicles, most people will not really be able to tell the difference.
In most traditional 4WD vehicles, the drive from the engine is sent to the rear wheels by default, through a box known as a transfer case.
All-wheel drive (AWD) doesn’t use a transfer case, but uses a system that delivers torque to where it’s needed most, still allowing for individual axle speeds. In many AWD systems the engine drives a front-mounted gearbox, which drives the front axle through the front differential first. Some of them power the centre differential first which can then send most of the torque to the rear axle – so not all AWD vehicles are the same.
An on-demand AWD vehicle runs in two-wheel drive (normally front wheels) by default – but when the front wheels begin to spin, sensors detect the loss of traction and redirect torque to the other axle to ensure maximum grip. The reduced friction of driving two wheels most of the time will use less fuel that a full-time AWD system.
In most Australian road conditions, all you need is a two-wheel, front-wheel drive. If you want to race in a high powered vehicle, you will choose a rear-wheel drive.You would go for an AWD vehicle if you need the safety of all-wheel traction in conditions like dirt roads, snow or wet and cold mountain roads, and then a constant all-wheel system is best, with next-best being the on-demand systems. True 4WD systems are really only needed for really rough terrain, or extremely muddy conditions.