Eliminating the Dreaded Audi RS Understeer – Part 2

In Part 1 of this series, we identified the hurdles that our C6-generation Audi RS6 will have to overcome to become an agile cornering machine. After our thorough test-drive, we identified these issues:

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

We decided the best course of action was to install a few key upgrades in the areas where the biggest improvement to handling could be achieved.

The C6 RS6’s biggest dynamic flaw is understeer when cornering hard. The understeer is most noticeable during the mid-corner and corner-exit phases, which makes the car frustrating to drive quickly.

The second issue the C6 RS6 suffers from is its heavy weight. Weighing in at over two tonnes does the RS6 no favours in the handling department, and immediately put us at a disadvantage when trying to improve the handling.

Whilst removing the RS6’s understeer is our primary goal, upgrading parts can also be a smart choice when looking to give an older car a new lease of life. Our RS6 is a 2009 model, and even with careful use and maintenance, a 14 year-old car will not be as fresh or tight as it was when new. This challenge would provide us with a chance to improve and refresh our RS6’s suspension.

The first upgrade was to install uprated front control arm bushes. The RS6 features a multi-link front suspension layout which is effective for kinematics and packaging, as it does not take up much space. We changed the bushes in the upper control arms for uprated offset bushes from SuperPro. When installed correctly, the offset holes in these bushes change the geometry of the front suspension, increasing negative camber and increasing positive caster.

Whilst these bushes have a relatively small range of adjustment, the additional negative camber and positive caster makes a huge improvement to the RS6’s handling.

Increasing negative camber is an effective method of eliminating understeer. When cornering, the car will roll onto the tyre’s contact patch when cornering – this rolling onto the tyre forces the outside tyres flat onto the tarmac, which generates the maximum amount of grip available from the tyre. As the outside tyres deal with the majority of the cornering forces, this more effective use of their contact patches greatly increases cornering grip.

An increase in positive caster is another good way of improving cornering performance. Positive caster is useful as less negative camber is required (which means improved straight line stability and braking performance) to achieve the same cornering performance. Positive caster creates a self-aligning torque. This torque increases straight line stability and also steering feel, making it easier to place a car more accurately in a corner. The increased positive caster creates dynamic camber gain when cornering; the outside wheel will gain negative camber during cornering, and the inside wheel will gain positive caster. This effectively leans the car into the corner, helping to put the largest available contact patch to the tarmac. 

The second issue we wanted to address was the performance of the original springs and dampers. Whilst Audi’s Dynamic Ride Control (DRC) is clever and offers a variety of suspension settings for different circumstances, in terms of outright performance, the system is not the best for outright cornering performance. Another issue with the DRC system is that installing aftermarket suspension components is difficult as the system needs to be bled of hydraulic fluid before the shocks can be removed.

Unfortunately, the C6-generation RS6 did not sell in huge numbers, therefore aftermarket suspension options are limited.

We opted to fit a set of KW V3 coilovers to our RS6. The KW V3 is an excellent all-round coilover; they feature 2-way independent adjustability (16 clicks of rebound, 12 clicks of compression), ride-height adjustability, and are stainless steel plated for protection from water and salt. The uprated springs and dampers on the KW V3s help to improve every aspect of the RS6’s performance, with improved body control and directional stability, more traction and increased braking stability too.

The higher performance springs and dampers generate more grip as the springs contain the excessive movement of the mass of the car more effectively. The uprated KW dampers control the movement of these springs more precisely, especially when using the independent compression and rebound adjustment to fine-tune the characteristics of the handling. When installing the KW V3s to our RS6, we made sure to tweak the both the bump and rebound characteristics in order to help chassis rotation when cornering.

As KW V3s are fully ride-height adjustable, we can also benefit from altering the ride height in order to improve vehicle dynamics. The first change is to lower the overall ride height. A reduced ride height helps to improve body control and stability. By reducing the ride height, the suspended chassis and body has less inertia during all aspects of driving. 

After lowering the ride height we also put positive rake into the RS6’s chassis. Positive rake is achieved by lowering the front ride height more than the rear. This lower front ride height helps to reduce nose-diving during heavy braking, and also improves turn-in, thanks to the reduced weight transfer during the initial phase of the corner. The final dynamic improvement we looked to achieve was to apply a full corner weighting and alignment setup to our RS6.

Corner weighting is the process of adjusting the ride heights on the coilovers at each of the four corners of the car. The ride heights are altered very slightly in order to balance the mass of the car and driver evenly across all four tyres. This is to ensure each of the four tyres is generating the maximum amount of grip each. If done correctly, corner weighting improves cornering, acceleration and braking performance, making it the most effective way of maximising the potential of aftermarket coilovers.

Alongside corner weighting our C6 RS6, we also applied a full fast road geometry alignment. The settings we applied will make the steering more responsive and positive during turn-in; they will help to reduce understeer and increase mid-corner grip thanks to the increased negative camber; and they will improve acceleration as each tyre is working evenly to develop maximum amounts of grip.

With the upgrades fitted and the RS6 fully set up, there was only one thing left… to take our new-and-improved C6 RS6 for a full shakedown and test drive.

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