Quote:
Originally Posted by LAP1DOUG
OP, I am running pretty close to the same set-up as Stone, which looks like good advice to me. I will add a few points that I have found:
1- Ride height, camber, and toe are all highly inter-related with this supension geometry. If you are running coilovers, then you must fix ride height & corner weights first before even thinking about camber, caster, and toe.
2- If you go too low on the rear, you will have too much negative camber, and run out of toe adjustment. This is one of the reasons that some people use rear adjustable toe links on these cars. I feel it is better not to go that low, but the after market toe links are still good to eliminate rubber bushing deflection, and be able to shim the upright attachment to adjust bump steer.
3- Optimum front to rear tire stagger is a function of what you do to optimize camber. If you don't modify camber to get near -3 deg as Stone suggested, then the optimum tire stagger will be close to "square". (something like 255 F / 265 R). However, if you crank in enough negative camber to optimize the front tire, then you will need more stagger - something like 255 F / 285 R, with the appropriately correct wheel sizes of course.
4- A GT3 front bar is the best mod you can make if you do nothing else. If you get it set at just the right roll stiffness, it will help reduce understeer by reducing the amount of positive camber in roll that all McStrut designs (911 or 986) experience. However, if you you think a little is good, then a lot is better, it will understeer like a pig.
5- If you use coilovers, go with fairly high spring rates to better control dynamic camber and toe changes. If you use a significantly higher spring rate in the rear, you may not need much or any rear bar. It is a fine balance with these cars, and sometimes a relatively small change in roll stiffness at one end can result in major oversteer or understeer. I suggest testing all new set-up changes on an auto-x course before heading to a track.
Hope to see you at a Southeast track sometime this year.
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Well thank you for the write up. This is what I'm looking for. I am using coilovers (H&R) but not going crazy for just DE's.
I've not run mid engine cars before on track. My race car was a water cooled GTi. Stiff as you could rear and I always ran soft front, the car was on rails.
The 993 was similar but I cooked tires without enough camber. I'm thinking this time about adjustable camber plates for the front to dial in 3 degrees (or as close as possible).
I'll be running 8" hollow 996TT 18" wheels with Yoko slicks and thinking 35-40mm spacers with studs (questions, concerns?) to get effectively 9.5 width without all the weight of 9.5" rolling weight.
Figure I'll start there. Look forward to your responses. And I will be at VIR with Zone 2 PCA mid March. If you're there, love to meet in person. You won't miss my car
(more to come)
Thanks