Apex Late

Here is what I am going to shoot for........
Front camber -3.0
Front Caster Max
Front 1/8 toe OUT EACH SIDE
Front sway bar middle position
Front ride height lower 1/2"

Rear camber -2.75
Rear 1/8 toe IN EACH SIDE
Rear sway bar full stiff
Rear ride height lower by 1/2"

Wing: 8° AOA
Cup Car front Splitter (do you have a part number for this????)
Rear Cup Car toe links
Solid motor mounts (leaving tranny mount Cadillac sponge rubber for now)

I will first admit that I'm not really up to speed on toe and how it is calculated but isn't 1/8 per side a lot of toe? I think that I'm running 1/8 total or 10 min total in the rear right now and its VERY stable.

lawjdc

The increased rear width of the RS could very well be contributing to the low speed push. Is there room in the front to add the 5mm spacers? That might balance the car better in the low speed corners.

insite

if you're really fighting push, why not go 1/16" toe per side in back? also, lower the front a full inch if you can, but leave the rear at 1/2" lower. this rake will fight understeer. also, what is 'max' caster on a 997 GT3?

suprisingly, i haven't heard a single person mention tire pressure in this thread. someone did mention that the rear tires for the 997 get more contact patch than the 996 did, but the fronts are the same. try dropping your rear pressures and upping the front.

doc2s

remember unitah had -2.75 camber front and front sway bar was not full soft and had a hint of understeer he might have been able to dial the understeer out witht the bar. increasing front camber to -3 and dropping the rear to -2.3 will hopefully make the rear loose and then play with sway bars on the track if needed.

let us know how things turn out and what the "current" specs will turn out to be.

frayed

lawjdc, this is affecting Bob's RS and the other two 3s as well so it appears not to be limited to an RS issue. Also, my experience playing with spacers and offsets shows very moderate, if any, change in balance of the car. 10mm extra track over the full length of the track is really small.

Insite, I think Apex said above he already fiddled with pressures.

Interestingly, NJ-GT's experience in Bobby's RS didn't reveal heinous understeer in low speed tight corners (autox). OTOH, early reports on the car were of unyielding understeer. Strange.

https://rennlist.com/forums/showthre...ight=911+world

Bob Rouleau

A few comments - annoying understeer was present on 2 RS and a GT3. It is not unique to the RS with it's greater rear track.

We played with tire pressures. The Cup tires usualy like 32F 34R on a 996GT3. I went higher and lower and increased the differential between front and rear pressures without a lot of success. Ron went so far as to lower the front hot pressures into the 20's to try and cure things. He felt a slight improvement.

Insite once tires are within the acceptable pressure window (range) lowering the pressure normally increases grip. Lower pressure in the rear would have made matters worse I think.

Lower pressure in front (within the acceptable range) would increase the front contact patch and decrease understeer.

I went higher in the rear but it don't help. Mine was the worst case since I have an as delivered alignment and my front bar was one from soft and the rear was one from stiff.

Here's a question: The suggested race alignment in the manual is zero toe in front with neg 2.5 camber. In back toe is 16 mins - is that total or per side I wonder? Rear camber is neg 2.3.

I am leary of too little toe in back since the car might get skittish under braking.

best,

AllanJ

Peanut gallery comment here: Rad is a professional autox-er. I figure he could tell the difference between 0.00002 degress of camber from side to side.

Something I've found in autocrossing my 996 GT3 is when driven poorly, it'll understeer like a typical FWD econobox. However, drive it right and the turn-in is amazing and you'll have a ton of grip.

I'm not fiddling with my car anymore....I'm going to fiddle with the nut behind the wheel.

[ edit: The 997 GT3 is going to be a slightly different animal from the 996 GT3 so my guess is folks might need to relearn how to drive it when pushed to its limits as you guys are doing. ]

Cheers,

Apex Late

No disrespect here but this set up won't work on the 997. Firstly the rake you are talking about is not compatable with the PASM. By implementing what you are suggesting the car will bounce like crazy on any small bumps and come clear off the ground on big ones. As for the Tire pressures we have been using 32/34 and have tried a number of combinations. BUT increasing the rears as you have suggested would only make a push worse. I think you may have meant dropping the front.

Apex Late

Hey AllanJ,

Although I would never suggest that I could feel .00002 degrees of camber I think that I do an ok job of driving cars correctly. That being said I too can "fiddle with the nut behind the wheel" and I'm constantly doing that in a effort to become a better driver (that is why I believe in PCA DE's and participate there on a regular basis). If myself, Bob or Ron felt that the problem was driving style (or the nut) I assure you we wouldn't be on here looking to the community for answers. You see you can't start to work on the nut behind the wheel until you get a car that does what its told to do by that nut.

In this case these nuts have more than a little driving experience not only with Porsches but performance cars and race cars alike. Although we are not Pro Autox-er's (I didn't even know you could go pro in this regard) I believe that we have all competed in Professional Race series and have held the credentials necessary to do so.

doc2s

at least for street front toe is quoted as total (6') rear is quoted per wheel (13'). i assume it would be the same for the suggested track setup. rear toe is increased fo added high speed stability.

my manual show -2 camber fr and -2.5 rr for track.

AllanJ

Completely understood and I meant no disrespect. My comment was more about Rad playing with a car. From everything I've read about him he's got some serious talent.

If you compare autox to track, in autox there are way more turns going on and way more places where the car is transitioning from side to side. The suspension is settled, then not, then back to settled again, all in a very short period of time. In autox you might have 20 turns done in the same time it takes you to do 4 or 5 at a track. To master that - consistently - takes a lot of skill and Rad has that.

I sure don't have it. BTW, the "nut" comment was about me, not you guys.

Cheers,

Apex Late

No worries Allan. We are all "nuts" to be doing this stuff with such expensive toys! Enjoy the ride!

Racerron

I don't know what you would have to do to make a 996GT3 understeer as badly as an RS..........maybe remove the front tires completely!

Crazy Canuck

Would the Traction Control and/or LSD contribute to the understeer you guys are experiencing in low speed corners?

Bob Rouleau

Chris - all of tried button pushing - TC on Off, suspension hard - normal and sport mode on/off. The understeer remained. The LSD on the 997s is less aggressive than the 996 according to the specs. I suspect that there is an intercation between the LSD and TC which requires less lock up on cars so equipped.

I am confident that the problem is related to suspension settings. Since the new GT3s are far more street friendly than the previous model I think Porsche dialed in understeer to prevent specious lawsuits from people who crash because hey can't drive and blame the car instead. Apex and I are experimenting with different setups after consulting with race teams running the 997 Cup. I'm testing mine at Tremblant tomorrow. Apex is testing his at Calabogie today. We'll post our results.

Just in case anyone has missed the point, the RS and 997 GT3 do not understeer at moderate speeds. On the other hand since the back end of the car is planted in bedrock, one should be able to go faster. That's when the push happens. Driving too hard you say? Well perhaps, but explain why a 996 GT3 pulls 5 forking car lengths on us in the same corner!

Best,