Tire Sizes

I've got a 2000 996 with 18" Sport Design wheels and the following tire sizes: Front 225 40 18 Rear 285 30 18 First, I'd like to try 285 35 18 on the rears. Is this acceptable? Is there any reason why I wouldn't want to? I'd also like to use a wider front tire (maybe 245). Any issues with that? Thanks guys.

What is your objective in changing the tire sizes? I am no expert, but I think that going to a wider front tire with the same rear width is going to increase understeer. Going to a taller rear tire is going to give you more top end but less acceleration. Is that what you are trying to achieve?

Also, I believe you'd need new wider front rims to take the 20mm wider tire. That's almost an inch. If you're just lookking for a better "look" in front ie wheels closer to exterior, try spacers. For the cost of 4 tires plus 2 wheels you could probably lower the car and get a nice look that way. Just a thought.

The 35 series rear tire would be about 3/4" (3%)taller. It should ride smoother and quieter, and would be less likely to bend a wheel on a bad pothole. You could run lower pressure for an even smoother ride. The speedometer would register 3% lower, which would make it MORE accurate. Visually the tire would fill the wheel well more and the rear of the car would sit about 3/8" higher. Breakaway at the cornering limit should be more gradual and predictable. However on the track the car may be slower. Because of the taller gearing acceleration would suffer slightly, and the car would tend to be more loose/sloppy and scrub off more speed in corners. The tail might overshoot a little in quick transient menuvers. You could probably tune out most of the minor handling issues with more air pressure though. The wider front tires may stick better. They would be more likely to hydroplane. They may follow grooves more and give more steering kickback.

Thanks guys. I appreciate the comments. Don, I have lowered the car already with H&R coilover kit. One of the main reasons for the question about sizes is because I want to try some other tire manufacturers (like Yokohama) and they don't make the 285 30 18. As for the wider front, I just thought it might look better and give a bit more traction. Maybe a 235 on the front?

Why would a wider tire on front increase understeer? if anything, I'd have thought the wider fronts would just hold on better, and increase the likelihood of oversteer.

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica"> Why would a wider tire on front increase understeer? </font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Well, first off, by increase, I of course meant decrease <img border="0" title="" alt="[Wink]" src="wink.gif" /> . Like I said, I am no expert, but the tire offset (smaller in front, larger in the rear) has been described in many places as designed for understeer, less of a street/track issue, more of an autocross problem. My freinds who autocross (I do not) seem to follow two dictums: 1. Put as much rubber as you can on the road. Since the body design allows wider tires on the rear, they go as wide as they can without rubbing. 2. Minimize the differential front-to-rear by putting as wide a set of tires up front as you can(but see above on rubbing/rolling the fenders, etc.) to minimize the understeer. My original question was motivated because I thought he might be a budding AX guy, inwhich case a wider front tire would make sense.