Attn Track Junkies...Tire Size and Wear Question...can I run 245 40 18/295 30 18?

Hi guys I currently have factory 18 inch turbo twist wheels on my 99 996. I am running Continental Sport Contact 2 tires size 285 30 18 and 225 40 18. I am preparing my car to do a few open track events. I just got a great deal on two rear tires ( mine are shot). They are Continental Sport Contact 2 size 295 30 18. My front tires appeared to have plenty of tread left (50%) until I examined them closer. They are excessively worn on the inside. I just had the car aligned about 4 months ago by the dealer. Any ideas what the problem is? I have an extra mis-matched tire on my wife's SL that I need to replace. It is a almost new Continental Sport Contact 2 size 245 40 18 with about 95% wear left. Can I buy a mate for it and use it on my 996 without any problems? I plan on upgrading my suspension in the near future to the ROW M030. Thanks for any advice.

wrong tire pressure, possibly ? (for the wear) I don't know about your upsizing, esp in the front, but you will like ROW030.. I sure did... Also, prepare to lower the rear pressures a lot on track... The factory 44 will quickly lead to 50+ pressures, which is insane !

Thanks for the info greg. I'm looking forward to upgrading my suspension. I'm amazed at what a bargain it is.

Without the use of a probe pyrometer and the specifications of your alignment, it is hard to know what the problem may be. The symptom you descibe does NOT sound like tire pressure. Rather, it "sounds" like you have too much camber for your driving style. Loads of camber is great for cornering on the track IF you are driving hard enough that your tires are level when you are going through the corner. If you only drive on the streets or are not driving fast enough, your tires never roll over and you only wear the inside edges, which "sounds" like what may be happening in your case. In the end, though, It is nearly impossible to tell without more information. This taught you a good lesson, though. You really need to be careful when you inspect your tires. I had the same problem with a set of tires when I very first started doing track events, and it caused my to hydroplane very briefly at 100+ mph No harm no foul, apart from the "crap" I caught from my wife when she saw my shorts P.S. Do NOT screw around with mismatched tires. Life is too short and that is too risky. Buck up, open the wallet, and don't skimp on the single most important safety item on your car (and, in my opinion, far more important than anything else apart from, perhaps, the brakes, but then again, brakes don't matter without tires capable of generating negative gs . . . ).

TD thanks for the info on the alignment. I had a similar problem with my Saleen track car when I drove it on the street after having it set up with a track only alignment. I destroyed a set of tires in a few hundred miles. I suspect you are right about too much camber...I did not ask the dealer to align it for the track. I wish I could drive it hard enough on the street to get away with the current settings. I also appreciate the advice on the mismatched tires. I have lost brakes a couple times on the track in my previous car (too much engine...not enough brakes). I don't want to repeat that. I replaced my front brakes with new oem parts. I just ordered new rears yesterday. I am upgrading to stainless lines and better fluid (any recommendations?). The mismatched tires were on our SL when we bought it back in December. It had Pirelli's all around and one Continental on the front. I would love to use the Continental on the front of my 996 along with another new one (if I can). If not, I will buy new fronts also.....should I get 225s or 245s? Thanks again for the help.

No worries. Keep in mind that stainless steel lines are not necessarily an improvement. In fact, many track rats advise against them because they make inspection more difficult. Plus, if the rubber lines are in good shape, they will not contribute to a mushy pedal. I used Castrol SRF in the 996. It is expensive but it is the bomb . . . by far. I always stuck with stock recommendations for tires. There is a reason why they picked them.

Isn't 225/285 the wrong tire combo? IIRC your car should be running 225/265. I would think 225/285 and even worse 225/295 would be giving your car tremendous understeer which will certainly not be any fun on the track. Go back to the stock sizes, or better yet, upsize front & rear equally. Try running 245/35/18 and 285/30/18 and your car will handle better.

Mark, I appreciate your information. I have previously been told by members of this site that the 295s will not be a problem on the back of my car....I'm trying to figure out the correct front size to go with them. I have an almost new 245 45 18 tire that I would like to use. Does anybody know if it will work? For what it's worth, I have been running the 285/225 combo for the past six months. I take the car out on a challenging local road on a regular basis. I have not expereinced any issues with understeer. If anything, the car is prone to oversteer. I have had a couple occasions where the rear tried to overtake the front. Once I countersteered, it was very controllable.

Mfletch, You should also consider your wheel widths when choosing tire sizes. For example, the 18" widths for the 3.4L cars are 7.5" F / 10" R. The factory tire sizes for these wheels are 225/40/18 and 265/35/18. When Porsche upgraded the 996 to the 3.6L engine, they increased the rear tire size to 285/30/18 while retaining the 10" width. However, they increased the front wheel width to 8", while keeping the tire size the same at 225/40/18. When Porsche goes to a 295/30/18, they go to an 11" wide wheel.

Kevin, my 18 inch wheels are off a later car. They are 8 inch in front and 10 inch in the rear. With the 11 inch rear wheel, did they use the 225 in front? Other members told me that they are running the 295s on a 10 inch rear with no problem. I got the 295s for about $200 less then the normal price. I thought I would give it a try. Given the car's appetite for rear tires, if I don't like the size, I won't have to live with it for long. Thanks for the info.

Yes, with the 8" wheel, as on the Turbo. Porsche does specify a 235/40/18 for the 996 GT3 and GT2, but these are mounted on 8.5" wide wheels. The 996 GT3 has 11" rears with 295/30/18's, The 996 GT2 has 12" rears with 315/30/18's.

Kevin, thanks for the info. I really appreciate it.

You're welcome.

Your question is timely as I am just returning from my local tire installer. I tried to put 245/40 - 18's on my fronts (my wheels are 0.5" wider than stock) and they rubbed the front liner on partial lock. The width was fine clearing the fender, but it did rub the front of the liner when I turned the wheel. I'd imagine 245/35 - 18's would just fit with my current offsets (GT3 size wheels). The rears 295/35 - 18's on 11" wheels fit fine in back. Looks like it's back to the drawing board for me. I think I'll end up with 295/30's in back and 235/40's up front. Good luck!!

Thanks Ray. I just got off the phone with Damon from the tire rack. He was very helpful. He told me that the 295s would work great on the rear of my car. He told me to stick with the 225s on the front. He quoted me a price of $170 for the fronts (Continental Sport Contact 2) which I thought was a fantastic price. Now I just have to get the dealer to fix my alignment problem. Good Luck.

I'd go with 235's up front. That way you'll have GT3 sizes all the way around.

Ray, I will certainly check into the 235s when I change the fronts. Unfortunately, that's probably the closest I will ever come to having a GT3. Thanks for the info.