cid042

Hi all,

At this stage, I need quite urgent help on this : This season, we enter a 996 GT3 (road car) in a championship where Michelin Sport Cup 2 are the mandatory tires. It is highly modded as a racecar : Central lock, stripped interior, and so on. This car was run with slicks till now, and set up with 996 cup springs (240 Nm/mm front & 260 Nm/mm rear). The 996 GT3 RS (Road car) was delivered with 45 Nm/mm front springs and 90 Nm/mm rears.

With the Sport Cup 2, the car bounces and everything proves that the springs are far too stiff.

We have ordered a study to a well known company to define the best spring rate, and thay conclude that it should be 160 Nn/mm front & 220 Nm/mm, and that seems still too high from my point of view. We have not changed anything yet, and do not want to do this 3 times to achieve a good setup. We have as much smooth track as bumpy ones in there (think Dijon, Magny Cours, Ledenon, Paul Ricard, Le Mans...).

Long story short : May anyone help us in choosing the good spring rates for this car ? It is not for an international championship, but as we all know : Do it once, do it well ;-)). The dampers will be revalved 996 cup (early ones, no adjustment).

Key facts :
* Weight : 1455 kg in total, with driver and half a tank
* Weight at the wheels :
* RL : 459 kg
* RR : 436 kg
* FL : 292 kg
* FR : 268 kg
I do not know the motion ratio, but it is the standard 996 GT3 one, if that may help. The car do not have rose joints in the suspension.

Many many thanks for any help !

Kindly yours,

Cedric

Rickard 993 Turbo

lordpantsington

MR should be around 0.98 F, 0.75 R.

cid042

Many thanks for your quick answers & infos !

Rickard, was your GT2 (996, I guess) the same weight that my GT3 ? Not using slicks ?

The Ohlins basic kit (Road & Track) is sold with Front 70 Nm/mm & Rear 140 Nm/mm springs which is far lower than 160 / 220.

I really get lost :-\

Rickard 993 Turbo

AudiOn19s

**non-professional opinion** Ohlins is about the only manufactuer who likes the lager spring split front to rear like that. Most of us who have been running 996 GT3's for years have found a much smaller split seems to work and balance the car better. Forgive the conversion to in/lbs here but most of us are running a spring split of around 100min to 200 max from front to rear.

I also think a lot of the bouncing is going to come back to the dampers more than spring rate. There are forum members with similar weight cars to yours that are running as high as 1900 F / 2000 R lb springs in their cars and running on 100 treadwear tires. They are running pretty advanced motorsport 3 way dampers though.

My personal car is only slightly heavier than yours and i run 750 F / 900 R springs with 100 treadwear tires and feel it's too soft for a dedicated tack setup, but I still drive mine on the street so that's where I ended up. I also have JRZ 3-way motorsport dampers and like to rum them on the softer side compared to others.

I don't think the rates you were given are far off ...they equate to 900 F / 1250 R in/lbs. Again that's a larger split than most use (other than Ohlins) but I don't think the rates in general are all that far off from where you should be.

pete95zhn

I'm running 120 & 160 N/mm, split is IMO quite OK but springs could be a tad stiffer. MPSC2's, weight is more or less the same*. Shocks are revalved Bilstein Cups with 3-way adjustment.

* 75l fuel, 90 kg driver:

cid042

Many thnaks for the inputs, Guess I now have to try this 160 / 220 setup ;-)

AudiOn19s

interested to hear the end results. Again, i'm curious if the damper is more of the problem than the springs when it comes to the bouncing

cid042

I will post my first review after the race at Dijon in June ;-).

powdrhound

People are scared of stiff spring rates. It's all about the shock$ to make it work properly. Made a believer out of me. IMO, if you are getting a lot of bounce then your shocks are not set up correctly or simply don't have the ability to handle the chosen spring rates. What dampeners are you using?

spiller

cid042

Thanks for your feedbacks. I am using stock 996 cup dampers, non adjustable.

Glen

bilstein can revalve for you. I liked adding to the rebound, making car slower to come back up using stock cup spring rates.

Laurence Gibbs

Can't say i have noticed any bouncing in my 02 Cup running MPSC2 . Not had a massive amount of seat time mind you.And this was on Brands Hatch Indy, which is pretty smooth.