Eliminating the Dreaded Audi RS Understeer – Part 1

The Audi RS performance range is synonymous with two things: big power and lots of traction thanks to Audi’s famous Quattro AWD system. Unfortunately, Audi RS cars, from the S1 to the R8 supercar, are also renowned for possessing a third characteristic which is much less desirable: understeer.

This understeer exists for a reason – it works as a safety net, telling drivers when they are pushing their luck when driving fast. Audi has a duty to make sure their cars are safe for all drivers and using understeer as an early warning system makes sense. The key reason is that understeer tends to be more easy to recover from, compared to oversteer.

For enthusiastic drivers that really enjoy pushing the limits of their Audis, the understeer safety net becomes an annoying obstacle, as it limits cornering speeds and forces drivers to slow down to eliminate it.

Here at Suspension Secrets we are often tasked by our Audi customers to help reduce understeer and to improve the chassis balance.

Whilst reducing the understeer in Audi RS3s and TTs is quite easily achievable, with some easy tweaks such as camber adjustable ball joints and a stiffer rear anti-roll bar, we wanted a challenge. After a quick debate here at HQ, we opted to take up a challenge: to take the most dynamically flawed fast Audi available and make it handle well.

There was one clear choice when it came to deciding which Audi has the biggest tendency to understeer: the twin-turbocharged V10-powered C6-generation Audi RS6. Weighing 2100kg and measuring 4.9 metres in length, the C6 RS6 was never going to be the best handling car ever made, especially as the entirety of its 571 bhp 5.0 Litre twin-turbocharged V10 engine sits ahead of the front axle. The mighty V10, designated BUH internally, weighs in at 278 kg and you don’t have to be a chassis engineer to recognise that having over a quarter of a tonne of metal ahead of the front axle is not the best recipe for nimble handling.

Driven by their desire to make the C6 RS6 far more powerful than its in-period rivals (the 507 bhp BMW E60 M5 and the 518 bhp Mercedes E63 AMG), Audi’s engineers persevered with their 5.0 Litre twin-turbo V10 and elected to use advanced technology in an attempt to make the C6 RS6 at least somewhat capable on a twisty road.

To improve the handling of the C6 RS6 Audi fitted the car with their Dynamic Ride Control (DRC) suspension. DRC features 3 selectable modes: comfort, dynamic and sport, with each mode making the dampers progressively stiffer. Stiff dampers are one way of managing the mass of a car, and Audi decided to take this a step further. The DRC dampers on the RS6 were hydraulically interlinked. This allowed the car to pump fluid to the individual dampers that were experiencing the most dynamic load, in order to stiffen the ride. As the RS6 entered a right hand corner, the system would pump fluid to the left-hand shock absorbers in order to keep the chassis flat and level.  This system effectively worked as a hydraulic anti-roll bar, ensuring the car remained somewhat composed during high-speed cornering. 

With all hardware analysed there was only one thing left to do: head out on a comprehensive test drive.

Firstly, let’s make one thing clear: the C6 RS6 remains an absolute powerhouse of a machine. 571 horsepower and 479 lb ft of torque give the RS6 a real elasticity when accelerating in any gear, and the way the car piles on the speed when into its stride has to be felt to be believed – it’s seriously fast and the hollow howl of the V10 defies those that claim turbocharged engines can’t sound exciting.

Whilst we were impressed by the speed of the RS6, it was time to get down to business and see how the big beast handled the twisties. One section of corners was chosen to put the RS6 through its paces; a fast third-gear left hander quickly followed by a short straight, which then suddenly plummets down into a challenging late-apex left that transitions into a tight second-gear right hander at the bottom of the dip that unwinds uphill into a long, fourth-gear left hander.

This corner complex tests body control; steering accuracy and communication; and chassis balance and it was time to see how the RS6 fared. On the approach to the third-gear left, one dynamic shortcoming became apparently clear: the brakes, or lack thereof. The brake pedal goes numb as the 390mm front discs do their best to slow the RS6’s massive momentum.

The heavy braking sends the mass forwards to the nose, and into the third-gear left the RS6 immediately feels uneasy and vague as the outside front tyre becomes loaded up and begins to scrub, with the understeer quickly becoming apparent. At this point the only option is to lift the throttle, dial in some more steering lock and wait for the Quattro system to grip and tug the nose back into line.

With the pace the RS6 carries, the short straight between the third-gear left and the upcoming downhill late-apex left hander vanishes almost immediately. The RS6 remains relatively composed through the left, but the second-gear right at the bottom of the dip that follows almost immediately highlights the heavy weight of the RS6, as it struggles for body control and feels tied in knots when asked to quickly change direction. 

The front washes out through the tight right hander, and as the throttle is fed in for the climb back up the hill, the front tyres scrabble for grip as the weight shifts rearwards. The Audi understeer re-emerges at the top of the crest, and another small lift off the throttle is required to get the nose back into line before applying full power onto the straight at the exit.

We ran this sequence of corners in both directions a few times and the feeling was the same. Even when experimenting with variables, such as reducing corner entry speeds and accelerating less aggressively, the Audi understeer was still present.

With our test drive complete, we were satisfied that the C6 RS6 had lived up to our expectations: it was massively fast but quickly got out of its depth when pushed hard in the corners. 

This is exactly what we wanted, and it made our mission clear. If we can make this beast handle with a neutral chassis balance and be able to exploit its power through the corners, then improving the handling of any other RS Audi would be a piece of cake.

Our analysis of the car’s chassis revealed the following:

• Understeer is most prominent at corner-exit when reapplying the throttle. 
• The understeer at turn-in is less pronounced than the corner-exit understeer.
• Finally, the most complicated understeer is during the mid-corner phase as the AWD system is working hard to keep the front wheels in check, whilst also sending power to the rear wheels.

The key factor to take into account is that if the turn-in understeer is removed, then the speeds during the mid-corner phase will be higher, which will subsequently increase understeer in the middle of the corner and at the exit. This means a comprehensive solution is required – simply reducing turn-in understeer is not enough. We need to ensure the RS6 handles nicely through the whole corner, and to do this we’ll be looking at making the chassis far more neutral and balanced compared to standard.

In Part 2, the RS6 will be in the workshop, where we’ll detail the upgrades and setup changes that we will make to the car. This’ll be followed up by a comprehensive test drive after the upgrades have been fitted to investigate how our changes have altered the dynamics of the car and whether or not we succeeded in achieving our mission.