mdrums

cbzzoom...the 245-40 and 305-35 in 18" is right at the same overall diameter as stock 19's. This is what I would go with and what I personal use at the track and have for the last 4 years. I did the 255-35 and 315-30 on 18's before and this works out great but the car needs to be lowered.

What you need to keep in mind is that the ratio bewteen the front and rear needs to be with in 4% so that ABS and PSM is not bothered.

cbzzoom

"I don't think matching the stock tire circumference is all that important, unless you're really concerned about the accuracy of your speedometer/odometer on the track"

- not at all, but I've heard it's important to get the ratio of front & rear sizes pretty close for PSM (and for the 4WD for me). Not sure if that's true or just heresy / wives tales. I guess if you're racing you're turning PSM off anyway.

.. but on your main point I'm definitely with you, the car is set up out of the factory to understeer, so I'd like to dial that out as much as possible. I think 245/295 might be the way to go.

stevencr

johnwb,
I have the same heavy lobsters on my 2006. I'm considering the 18 in. lightweight OZ wheels through tire rack. Have you looked at these?

Nugget

I've got a set of 18" O.Z. Alleggerita wheels I use for the track. They're light, but I hear they bend easily. I've got about 1,400 track miles on them so far and they're all still round and true. They're dramatically lighter than my factory wheels, for sure. I'm happy with them, and they were cheap. Fronts (8.5") weigh 18.166lbs and rears (12") weigh 23.446lbs.

I run 245/35 and 315/30 Hoosiers on them. Not sure what size would be available for R Comps. I've thought about trying a set of Nitto NT01s just to change things up one of these times.

utkinpol

what 12" allegeritas are you talking about? I was under impression OZ have only 11" wide allegeritas in the offset that fits narrow body cars?

What is that offset of those 12" allegeritas you got? Or do you have c4 car?

mdrums

Actually matching the stock sixe overall diameter is very important since the car has sensors that read wheel speed and g-forces (yaw ect). PSM either turned on or off will be affected and ABS will be affected. Smaller diameter tires will cause the computer to think the car is going faster than it really is and for example in a turn this could and will activate PSM differently than stock or how it was designed .

Also turning PSM off on a Carrera or Carrera S or Turbo car does not fully deactivate PSM and it will come back on. I have this happen under threshold braking and into trail braking or sometimes at the exit of a turn....I see the PSM orange light flicker on the rpm gauge telling me PSM was active. I have spoke with Porsche a lot about this and on these cars PSM is never fully turned off.

Nugget

Yes, I have a widebody (but not c4) car. I wasn't aware that the narrowbody offset wheels are a different width. That's a bummer.

utkinpol

tirack shows 11" alegeritas for my car with 63mm offset, damon I think wrote me once that 12" allegeritas have 68mm offset so it will require 7mm spacer to run on them but I am not going to buy light wheels to put spacer on them not to say I do not think tracking wheels should be mounted on spacers to begin with.

essentially 12" rim for narrowbody C2 or C2S should have somewhat about 60mm offset, maybe 58mm, but not into other way. And yes it is quite a bummer as I am looking for such wheel for quite a while now without much success.

Nugget

The stock rear wheels on my (widebody) car are 19x12 offset 51 (with 5mm spacer yielding an effective offset of 46). The 18x12 alleggeritas are the same offset (I use the factory spacer with them).

I shared your aversion to tracking with the spacer, but I figure Porsche probably knows better than I do and obviously they're fine with it.

mdrums

Call John at CCW in Daytona Beach. The GT3 C2 Narrow body set up is what you want. Offsets are perfect.

cbzzoom

A really extreme big front option would be :

265/35/18 Diameter: 25.30 in - wants 9.5" rim
295/35/18 Diameter: 26.12 in
ratio : 1.032

the ratios and diameters are good. 265 in the front will surely rub without a lot of suspension work though.

utkinpol

What did you mean with 'GT3 C2'?
Do you mean 996 GT3 wheels fit well into 997 C2? Do you know exact offsets values?

mdrums

Sorry I ment GT3 and C2 or C2S.

Off sets will change with various wheel widths. For 18" though I would go with 9x18 and 12x18. I believe the front offset is 50 and the rear is 63...John at CCW knows these exact and back spacing too.

utkinpol

yep, i think 50 front is right and for rear axle anything in 58-63mm should sort of fit... with 61 or 63 is probably to be the optimal one.

utkinpol

for those who is wondering about tires selections I actually found old very informative posting:

https://rennlist.com/forums/997-gt2-...-a-997-nb.html