S5 Sportback

quattro: what it does and how it works

Front-wheel or rear-wheel drive has certainly improved thanks to innovations such as electronic stability programmes, anti-lock brakes and traction control. But two-wheel drive cars will, particularly in extreme circumstances, sometimes exhibit certain (and usually undesirable) characteristics. 

Due to the weight of the engine and other assemblies resting on the front axle, front-wheel drive cars tend to be slightly superior to rear-wheel drive cars in the amount of grip they can transmit to the road during wet conditions. 

But in a front-wheel drive car, hard cornering or cornering on a slippery road surface can cause understeer: where the car continues forwards even though the wheels are turned. 

Conversely, rear-wheel drive cars can suffer from oversteer: the driving wheels deliver more power than the road surface can handle, causing the rear end to slide and the car to travel sideways. This can be quite difficult for you to control and traction aid systems and electronic stability programmes will engage quite early.

Slippery surfaces

With quattro, drive is distributed to all four wheels permanently in varying amounts, depending on the road conditions and how the car’s being driven; it’s constantly ‘feeling’ how much grip there is for each wheel. If a wheel loses grip, drive is diverted away to wheels that have better contact with the road. Because the ‘feeling-adjustment cycle’ happens continuously, it’s imperceptible to you and your passengers. All you notice is a firmer, truer driving experience, even in what would ordinarily be potentially dangerous driving conditions.

Cornering

With front-wheel or rear-wheel drive the car is effectively being either pulled or pushed round a bend. Instead, with quattro four-wheel drive, all four wheels work together and drive is delivered to where it’s needed and regulated where it isn’t. This means greater stability, more assured road-holding, enhanced agility and improved steering precision.