Hi all,

I run Nitron R3's on a 996.2 GT3 using 255/35/18 295/30/18 RE71-RS tires on 110/140 f/r N/mm springs. I run 2mm total toe in front, 4mm total toe in rear.

When the tires are new/fresh, when I brake hard in a straight line the car is rock solid and doesn't wiggle. It's when the tires are getting worn and have a decent amount of heat cycles does the car start to wiggle a lot under hard braking and the rear end doesn't feel that stable. Of course I adjust by being a lot more sensitive to brake pressure but ideally this doesn't happen.

Should I:

1) Add front compression. If yes, is it HS or LS? What damper velocity range is threshold braking?

2) Add rear rebound.

3) Do 1 and 2 at the same time?

Thanks!

 

Because every driver’s control input timing and amplitude is different, it’s going to be best to do some testing of the sweep, or range, of adjustments and note the result.

The slow rise time of most driver’s initial application to peak pressure from initial application makes the pitch change occur on the LS side.

You can go up in front compression damping in the front, but a “nervous rear,” if the driver is anywhere close to optimum rise time on the brakes, is usually more effectively addressed by reducing rear damping to allow quicker droop, hence keep the rear tire contact and loading higher.

I really would recommend doing a rather large sweep in multiple steps; a) just adding front compression damping from lower to higher, b) then reducing rear rebound damping from more to less, then c) go through the range parallel with both.

The problem is tuning the car on worn tires. If it’s working with new tires, it’s probably pretty good.

 

Reduce rear rebound? Wow that's opposite of my intuition. I would think I want to make it harder for the rear to go into droop and "pull the rear down."

Thanks for the recommendations.

But yeah I think you're right that if the car feels good when the tires are fresh then maybe I shouldn't mess around too much. I'll try front compression first.

 

I wouldn't not recommend to chase your setup after worn tires but rather see how you can get better rear tire wear. I assume you are running a LSD? 996/997 rear tire wear is very sensitive to rear toe changes.

 

Bias is the prime determinant for pulling both ends down at once. The split for street cars is almost always too much bias forward, for safety, IMO. The rears rarely are enough to pull the rear down with the front.

I think if you UP the rebound damping, on the initial pitch change, it pulls the rear tire compact patch up reducing tire load. But I think your plan to up LS compression in the front is a good first step on worn tires.

Just remember to set it back with new rubber.

I hate trying to dx shock issues without data. There is so much going on with the platform and the topography that it's super valuable, really mandatory, to be able to sort that out with discrete info with shock speeds and displacement is the only way to do it right.

The fact that you are evaluating that the car is good and settled, the way you drive it, with new or near new tires, sounds like it's pretty darned good.

 

Yes the car comes with a 40/60 accel/decel LSD, although I think mine is quite worn. I have a new one sitting here which is waiting to get installed.

 

Whats your rear camber? Im running 3.1* and 3mm of total toe and im seeing more wear in the inner edge them most 6-gt3s. U was gonna try 2.8* and a little less toe but my car is pretty stable under breaking as long as im smooth into the peddle. Im running standard r&t ohlins and a 315 rear hossier r7 tire with pagid yellows. Not the same set up but maybe it helps?