David Rotondo

I have a 02 996 coupe w/ 18 inch 5 spokes, & ROW M030. Currently Stock contis 225/285. Can I fit 245's on front to reduce understeer w/out rubbing issues. Is this a good Idea? Also, any benefit to add GT3 Sways?

I do both autocross & DE

Thanks

Russ Murphy

Here's a thread on RennTech (read Loren's post) that should answer most your questions relating to tire sizing.

As far as the GT-3 rear bar, heck ya!. I found it to be a great tuning aid.

996 MBA CFA

Nice link. I'm still a little confused at how much space is available in the front and rear with regard to fender clearance and spacers. Ideally, I could run 235/40/18 in the front and 295/30/18 in the rear. I think that is the GT3 tire size. Of course with spacers that changes the equation a little bit.

10 GT3

David, you won't get the benefit you are looking for because just going to a larger tire isn't going to increase the contact patch. It will change the shape, but not change the size of it. It also will not change the weight transfer. Actually, this move would make your problem worse. This is because the extra sidewall width will allow the contact patch to shift more on turn-in making turn-in slower.

Since you are running a ROW M030, providing you are running the right version for your car then the car should be extremely neutral. The ROW M030 increases the rear sway bar stiffness greater than the front and the rear spring rate and dampening increase around 25%. There are 2 areas you need to improve before adding suspension parts: alignment and tires. What kind of alignment are you running? Start by maxing the camber in front and running a half degree more than this out back. The Contis are the lowest grip of the OEM N rated tries. They are not very well suited to either of the tasks you are looking for them to perform. With DEs and Autocrosses you should be looking to move up to a set of R compound tires. This will improve not only the feel of the car, but also your times substantually.

996, if you are looking to run wider tires then you should be running wider wheels. A 295/30 is designed to run a 10.5-11.5" wheel. Considering the number of wheel manufacturers who make wheels in wider sizes for this car, you just need to get a set with the right offset. There should be no need to run wheel spacers.

David Rotondo

Thanks for the input, however, I have heard from more than one enthusiest on this forum that there is a benefit to increasing the width of the front tire, at least to a 235 (which can easily fit on an 8" rim. It is tough to judge, apparently, many have this type of configuration and are expressing some benefit.(better times etc)

Russ Murphy

One variable that was left out of the contact patch description is tire pressure. If you can lower the tire pressure (which should increase the contact patch area to some degree) versus the narrower tire to an extent that doesn't adversely effect the extent of sidewall flex than you would get an improvement of grip most likely. In a pure physics sense the dynamic 02 Carrera is describing is right on, but tires aren't symmetrically elastic like balloons. There was a previous thread on this specific topic that was very interesting.