Thanks for the specs Al... will let you know about those Pirelli's... will be trying them for SPA in a few weeks.

 

I think I'm going to go 9.5 and 12 too and may venture into a 10 and 12.5. The best size for tires though is 9.5 and 11.5. This is one of the toughest decisions evar because I'm really tempted to try that 10" wheel but do not under any circumstances want to deal with the headaches.

 

 

the stock uprights push the strut angles to less optimum position to allow the correct geometry. with the GT uprights you can rotate the upper mounts to gain more neg camber which will allow more back spacing.

 

Best size for wheels depends on size of the tire. The front tire I'm running really needs more wheel but I'm not going to venture into the 10" arena. If you want to jump in with 12.5 rears, I'll sell you my 2. Silver powercoat. If you aren't running the large turbos like I am they should work just fine with a good fender roll, some stiff springs and adequate rear ride height.

 

IMHO going to a extremely large front tire is a bandaid approach to understeer. Do it right and change sway bars and springs/shocks to dial out understeer and add adjustability to the suspension. Adding more negative camber will not eliminate the rubbing in the fender liner which is a function of tire width. With 250 x 650 18 Hoosier slicks I rub holes in the front liner unless I am very carefull to not turn the steering wheel more than 1/2 way. Even 245/40 will rub lightly.

Peter

 

In my case, I'm not trying to dial out any understeer. I don't have that problem. I am looking for the widest contact patch possible, both front and rear, thus the wide front tire.

 

it seems like trying to wide as possible only limits your ability to do any type of adjustments. trying to increase the widest contact possible would only hinder the handling.

you should have no problem fitting 10" w/ 275's with 5 degree of postive camber and shorter lower control arms.

 

Why would a wider contact patch hinder handling. That's exactly what a wider contact patch is beneficial for. Yes adjustment range is limited, but that's a small price to pay for more grip as the optimal range is still the optimal range when it comes to handling and fortunately the wider tire even helps put you in that range requiring more negative camber than less.


Peter: camber adjustments don't make up for the fact that an 8" tire is paltry with a 11 inch rear tire. The ideal way is to lessen the disparity between the front and rear stagger fitment which in itself causes some understeer. A bigger tire is as much a fundamental resolution as alignment changes, even though it must always be accompanied by a significant stiffening of the springs and sways. But doing all of the above is better than doing any by themself or any combination of only to.

Alignment
Suspension
Wheels

 

imho, going wide as possible and loosing the full potential of adjustablity of your suspension just seem unpractical.

 

you need to talk to cary eisenlohr. I think he went to 10" but reconfigured his total suspension to do it correctly. he had widen the fenders and change out the upright and all the side stuff.

 

Anyone going to a 10" wheel should be a near track only car, or AT LEAST willing to have an extra set of wheels for the street and willing to get alignment changed before and after each track event.

Having the 10" wheel is unpractical, but so is much of the stuff on a track car. Running -2.5 + degrees of negative camber is unpractical as well, but there are many doing it for track days. So is running r-comps on the street. But these are Porsche's, probably the most tracked vehicle on the planet and compromises will be made to be better at the track.

When it comes to the track, it's hard to classify much as unpractical, unless you're a novice and track 1-2 times a year.

 

with out the correct modifications seems like either way track or street it's unpractical.

 

OaK,

The only place I'm limited without front fender well modification is caster and ride height. I'm at 7.5 caster and the car works well with that. I've had camber at -4 in front and -3.5 in rear with no clearance problems with front springs. By checking tire temps it proved too much for my driving style which isn't very aggressive through the corners. I've dropped back to 3.5 and 3.0 but don't have much test data as that event was cut short by tire failure (left rear). I'm not sure what adjustment limitations you think I might have but I feel there is all the adjustment I need to achieve proper handling. The real adjustment hinderance I have is ride height. I don't want mine to be any lower than it is. With the outdated suspension geometry of the 996 it is pretty easy to get the roll centers below the ground which, of course puts them further away from the CG at that linear location. This means more body roll in cornering and necessitates more spring to control it. Even with narrower tires, you still can't really slam these things to the ground like you can a cup car.

Why do the factory GT3RSR's have such big flares on the fender wells? I think it's to enable them to run a fat tire and get the CG as low as is practical.

 

give cary a call.