Well, in front at least. CCW has been talking me into running a 10" C10 front wheel instead of a 9.5, for 275 (or 265) / 35 / 18 tires with sections widths around 10.9". I've been trying to make the 10" wheels (with 7" backspacing) work, but it's just too tight in the fender well. My most recent test drive, after deforming and pushing the fender liner as far away from the wheel as possible, still resulted in the strong smell of melting/burning plastic, after an aggressive test drive. There is about 10mm of clearance between the inner wheel flange and the front suspension lower spring perch, so I could conceivably have them shave 5mm off the mounting pad, but that would be cutting it close.

My setup:
front: -3deg camber (13mm of shims in lower control arm), rear: -2.5deg camber
wheels being tested:
front: 18x10, 7" backspacing, rear: 18x11, 7.57" backspacing

Apparently CCW has a few 996 customers running the 10" front wheel. If any of you are here, I'd love to hear how you make them work.

Al, are you still running the 9.5" wheel with 275 hoosiers, or have you gone wider? Do you think you'd have another 1/2" of clearance between the outside of the tire and the fender liner when turning?

Here's how the 10" wheel with 265/35/18 MPSC looks from the front:

 

That's not what your mother said last night Trebek

 

wow that's wide. what are the benefits of running a wider front tire on the 996tt and how if any does it affect the AWD function?

 

SOOOOOOOO glad you posted this, I've been tossing this back and forth for the longest. I know of at least one person that was running 10" wheels, and on a NB 996 no less. I think his inner wheel wells were cut out though.

The question is are you running adjustable lower control arms and camber plates both? I also found the tire selection to be bad if you are still running AWD, very hard to find the right overall tire heights within 1% at 10".

Here is what I think you will need to make it work, if you have it already or not is the question:

1) Adjustable lower control arms to shim the camber and increase the front track. (widen the lower part of the tire allowing more camber adjustment inwards without getting closer to the spring)
2) Caster pucks to reduce the extra caster that comes with the shimming of the lower control arms (this prevents increased rubbing on the front of the well while turning caused by increased caster)
3) Possibly camber plates (more negative camber is required and if caster becomes too big of an issue, then use the camber plates to help with camber and not effect the caster so much.


I really hope this works for you as I really want to do it myself. Keep us updated. I really want 10" front and 12" rear, maybe even 12.5", but after seeing all the issues that Al has had with cut tires (all rear of the car though) I want to avoid that at all costs.

 

Benefit is a much wider contact patch in the front which increases front grip and reduces understeer. Has no effect on the AWD. Only the diameters have an effect.

 

Hey Heavy, here are the full details of my setup right now.

GT3 lower control arms in front, with 13mm of shims. AWE/mode camber plates on the strut tops, (AWD specific in front), - which themselves only lend about -1 deg of extra negative camber. The 13mm of shims bring the front camber to -3 deg. This is actually the first problem area. The reason some GT3 guys (such as user NJ-GT) seem to be able to use 10" front wheels is that they can get all their negative camber from camber plates alone - up to -5 deg - without using the shimmed lower control arm. Widening the track reduces the clearance by a lot (> 13mm) at the outside of the tire, when it's turned in the wheel well.

I have to get the car up on a lift again and inspect the current rubbing... I already have my radiator ends relocated forward, and the fender liner moved forward about a 1/2". Now, it's been heated and deformed even more to gain clearance. I've stopped shaving my tire now - but under heavy corning loads something is melting/burning. I'll get to investigate more tomorrow morning. I suspect that these wheels are going to go back, and a set of 9.5" (with 7" backspacing) will be sent instead.

I was hoping that shaving 2/10" from the mounting pad (about 5mm) would give me all the clearance I need, but, I think that would only work if I doubled the front spring rate. Right now I use 500 lb springs in front, and 800 in back. I think I'd need to elimiate most of the compression travel, and use 1000 lb springs in front, if I wanted to run this 10" wheel.

There are other options though. The bodyshop started looking at what else can be moved, behind the fender liner, to open up some more space... but, this becomes a never ending cost/effort to try and make more clearance. I'm not sure it's worth the extra 2/10" inch of contact patch and slightly better steering response that the 10" wheel affords over a 9.5" wheel.

Still....it the grip and response are amazing. =)

Oh - regarding castor pucks. I have them, but haven't installed them. The reason is that the wheel is really centered between the front/rear fender liner right now... rubbing is about equal on both sides. Since the GT3 control arms have an offset mounting hole in their bushing, any adjustments can be fine-tuned there by clocking that bushing slightly. Ideally, I'd prefer to not reduce castor and give up the associated camber gain in corners. But for now, reducing castor any further than I have will just push the rubbing from front to back.

 

exactly... And, the diameters of the MPSC 265/35/18 and the 295/30/18 are pretty well matched. So too of the 275/35/18 & 315/30/18 combos out there... (nitto, hoosier, etc)

On a seperate note - in debugging another problem with the car, I've been driving around with the AWD center drive shaft disconnected.... and the difference is quite noticable!

 

Sorry to hear you're having trouble with your new setup, was really hoping to check it out at the PCA event!

Will you be at SP in oct?

 

Thanks Chasen. Unfortuntly I missed the last Time Trial for a different reason. Broken transmission mount. I'm out of points contention now... But, I'll still be at the next event.

 

The Ghey is very strong in this thread

 

 

How does the car feel w/o the 4wd? I want to try to do the conversion, but wouldn't make sense to do it w/o getting an LSD...

My dad got his best time over the weekend, so it was successful.

 

Ducati,

I'm still running the 9.5 CCW's. The 275 Hoosiers were never a problem. I'm now runniing a 265/645R18 Hoosier racing slick. It works fine also. I think I would have trouble getting a 10 under the front. I have 60mm springs on the struts and monoballs with lower shims for camber and the tire is very very close to the spring. The x-section of the 645 is close to the same as the 275 R6. Perhaps with a different offset and more fender rolling a 10 would work.

BTW, I don't advise anyone with large turbos to try running a 12.5 wheel on the rear. I've had nothing but trouble and expense. I think I may finally have the problem remedied but only the next track event will tell.

 

Al... currently running CCW 9.5" front with 265/35/18 and 12" rear with 315/30/18 and the front is tight already, hate to think what a 10" would be like... with the 9.5" I had to get my regular coachwork guys to widen the front fender/wing ever so slightly by around 5mm... the fronts would be ok but it did look a bit stupid with the wheel close the edge of the fender/wing so this is why I done this. I also have the Pirelli slicks and hope they fit ok, we tried the fronts and there was slight rubbing against the rear of fender liner (on the fronts) size of slicks are 265/645-18 with a rolling diameter of 2007mm the rears are 325/650-18 with a rolling diameter of 2007mm, I thought these were one of the smallest sidewall slicks available... do you have the specs for the Hoosier Slicks?

 

Steven,
I'm running the 320's on the rear. I will probably drop back to the 305's after I go through these 2 sets.

Here's the data you requested.
http://www.hoosiertire.com/specrr.htm#ROAD RACING SLICKS- RADIAL