Porsche Boxster S 986 Race Car set up advice please
Discussion
I would really appreciate some help in setting up the suspension geometry on my Porsche Boxster S 986 race car. I race the car in CSCC Modern Classics. The engine is stock. It runs generally on Dunlop Direzza or Toyo R888R’s. Cold pressures are 24psi and 29 psi hot. The dampers are Gaz adjustables. I am currently running with the rear anti roll bar disconnected.
I am really struggling to find a good set up that gives grip at the rear. On fast corners the rear breaks away under relatively light loads and when braking from high-speed the rear dances all over the place. The front-end grip and turn in has always been excellent. I am however really struggling to find a good set up that gives grip at the rear. On fast corners the rear breaks away even at relatively light loads. You can’t lean on it at all which means it is only on a partial throttle from the apex until it is near pointing straight again. When braking from high speeds the rear dances all over the place. The car seems to be generally using its tyres quite well. There is no obvious wear on the inside or outside both front and rear.
The car is ideal for my son and I to race together but I just can’t get any confidence in the grip of the car. When it does let go (and it does at relatively low levels of lateral force) there is little chance of getting it back.
I am reasonably used to the quirks of Porsche handling and I have run my 996 GT3RS on track (track days not racing) with none of this drama.
I would really appreciate some guidance on where to start with front and rear camber and toe.
Thank you.
I am really struggling to find a good set up that gives grip at the rear. On fast corners the rear breaks away under relatively light loads and when braking from high-speed the rear dances all over the place. The front-end grip and turn in has always been excellent. I am however really struggling to find a good set up that gives grip at the rear. On fast corners the rear breaks away even at relatively light loads. You can’t lean on it at all which means it is only on a partial throttle from the apex until it is near pointing straight again. When braking from high speeds the rear dances all over the place. The car seems to be generally using its tyres quite well. There is no obvious wear on the inside or outside both front and rear.
The car is ideal for my son and I to race together but I just can’t get any confidence in the grip of the car. When it does let go (and it does at relatively low levels of lateral force) there is little chance of getting it back.
I am reasonably used to the quirks of Porsche handling and I have run my 996 GT3RS on track (track days not racing) with none of this drama.
I would really appreciate some guidance on where to start with front and rear camber and toe.
Thank you.
When is it happening? Can you split the corner up into sections and describe the car’s behaviour in each? Fast, medium and slow corners? How much rear camber are you running?
Try re connecting the rear anti roll bar and increasing the bump and rebound on your front shocks as a start. If the car is as bad as you say it is you have a fundamental set up or hardware problem
Try re connecting the rear anti roll bar and increasing the bump and rebound on your front shocks as a start. If the car is as bad as you say it is you have a fundamental set up or hardware problem
Your problem is a complex one.
Because the rear suspension is a Macpherson strut it dramatically alters the rear toe as the suspension rises leading to bump steer. This is minimised in front suspension because the wheel also turns in and changes geometry as a result but at the rear it is a serious problem.
Also because the rear is not a double wishbone - the camber changes a lot as the suspension rises and that alters the surface area of the tyre that is in contact with the road and the more it rolls the more the camber changes and the less tyre you have gripping.
Furthermore - the more you lower the car the greater the camber change alters as the suspension rises.
What you can do about it depends upon the regulations you are racing within and your budget.
As the front grip is good despite having no rear ARB it suggests that the front is too soft compared to the rear. You need to stiffen the front (to put more load on the back - but then with no rear ARB you will get into bump steer again - so you also need to replace the rear ARB and possibly lighten the springs.
If you suspension has adjustable compression damping - this can help cheat the suspension into thinking the springs are stronger and that can help find the right direction to go in.
The easiest way forward would be to discuss the set-up of similar cars that are handling well with their owners.
Raising the rear higher than the front can also minimise the bump steer problem.
The same issues apply to the Cayman race cars - shame they didn't have the 991 double rear wishbones fitted - it would have made life much easier.
Good luck with it.
Baz
Because the rear suspension is a Macpherson strut it dramatically alters the rear toe as the suspension rises leading to bump steer. This is minimised in front suspension because the wheel also turns in and changes geometry as a result but at the rear it is a serious problem.
Also because the rear is not a double wishbone - the camber changes a lot as the suspension rises and that alters the surface area of the tyre that is in contact with the road and the more it rolls the more the camber changes and the less tyre you have gripping.
Furthermore - the more you lower the car the greater the camber change alters as the suspension rises.
What you can do about it depends upon the regulations you are racing within and your budget.
As the front grip is good despite having no rear ARB it suggests that the front is too soft compared to the rear. You need to stiffen the front (to put more load on the back - but then with no rear ARB you will get into bump steer again - so you also need to replace the rear ARB and possibly lighten the springs.
If you suspension has adjustable compression damping - this can help cheat the suspension into thinking the springs are stronger and that can help find the right direction to go in.
The easiest way forward would be to discuss the set-up of similar cars that are handling well with their owners.
Raising the rear higher than the front can also minimise the bump steer problem.
The same issues apply to the Cayman race cars - shame they didn't have the 991 double rear wishbones fitted - it would have made life much easier.
Good luck with it.
Baz
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