quattro

Front wheel drive

Front wheel drive allows the car to be pulled which increases the amount of tractive force it can transmit to the road compared to  rear-wheel drive. The weight of the engine and other assemblies rests on the front axle and thus increases traction to the driving wheels. If they start to lose traction, the front-wheel drive vehicle understeers and tends to continue straight ahead although the front wheels are turned. This is a relatively mild effect that the driver can normally control by simply lifting their foot off the accelerator.

Traction aids such as ASR and EDL are fitted as standard on all Audi front-wheel drive vehicles. Additionally the ESP Electronic Stability Programme greatly enhances what is already a high level of safety.

Rear wheel drive

The vehicle is pushed along by the driven rear wheels. As an initial situation, this is fundamentally less stable than with front- or all-wheel drive. If the driven wheels spin, the rear-wheel drive vehicle tends to oversteer and its tail may then slide sideways.

To guard against this situation arising, which the driver may find fairly difficult to control, the corrective action of traction aid systems and electronic stability programmes takes effect quite early. The vehicle can be kept moving safely, but traction is reduced by the need to apply the brakes at individual wheels, so that driving the vehicle becomes less pleasant.

quattro permanent all-wheel drive

Permanent all-wheel drive offers an unusually high level of active safety. In terms of tractive force, acceleration and hill-climbing ability on a poor surface it is unbeatable. By distributing the power input from the engine between two axles, higher lateral locating forces can be absorbed when cornering. This enhances lateral acceleration and at the same time ensures the highest possible level of safety.

To transmit their full potential onto the road, sporty vehicles like the Audi RS 6 and Audi R8 need a driveline to match. 

And the latest, enhanced version of quattro, featuring asymmetric/dynamic distribution of torque for the first time in an Audi, has set new standards in handling, agility and steering precision.

Asymmetric/dynamic torque distribution, with a rear-biased split, allows the exceptional driving forces produced by powerful engines to reach the road even more efficiently. It reacts to conditions on the road more responsively. And with more agility on tight bends, it delivers a more exhilarating performance than ever.

Once again, quattro raises the benchmark in high-performance engineering.  

Example 1: Ideal driving conditions

If more traction is required – when towing a trailer, for example – quattro offers real advantages by offering greater tractive force in proportion to the vehicle’s weight.

Example 2: Only 50 percent grip

In conditions where tyres experience reduced grip – as on a wet road – the advantages of quattro immediately become apparent. Whenever one wheel loses traction the others can compensate, so the car remains stable and continues to grip the road.

Example 3: Only the front wheels have grip

quattro continually adjusts to road conditions to permanently distribute power between the front and rear wheels precisely where and when required. It means the vehicle stays responsive even if only one axle has enough grip. By contrast, if front- or rear-wheel drive vehicles lose grip at the driven axle, they can no longer transmit the engine’s power onto the road.

The self locking centre differential sits at the heart of quattro on models with the engine positioned lengthwise along the car’s centreline, such as the Audi A4, A6, A7, A8, Q5 and Q7.

Operating entirely mechanically, it continually reacts to road conditions and responds to any differences in the rotational speeds between the wheels. This ensures more power is always transmitted to the wheels with a better grip.

In addition, the Electronic Differential Lock (EDL) can act when needed to prevent the wheels from spinning. Excess power at one wheel is diverted to the other wheels that have more grip, maintaining traction in virtually every situation.

To ensure the optimal distribution of engine power for each model, Audi uses specially configured all-wheel drive systems that vary in design.

The Haldex clutch is an electronically-controlled multi-plate clutch. It performs the function of the Torsen centre differential in cars with transverse engines, such as the Audi A3, A3 Sportback and Audi TT.

It ensures that engine power is permanently distributed between the front and rear wheels as and when required.

The Haldex clutch works by reacting to differences in the rotating speed between the front and rear wheels. This causes variations in the system’s hydraulic pressure, which in turn compress the clutch plates together to balance the distribution of power between the front and rear wheels. So if the front wheels begin to lose traction, the Haldex clutch channels power to the rear. And the greater the difference in rotational speed, the higher the pressure applied to the plates – which means that more engine power can be transmitted to the rear wheel.