275/35/18 vs. 265/35/18 on 2000 C4

Time for new tires all around. I've got 7.5" fronts, so I don't want to go to 285/30s on the rear, since I can't go wider than 225 on the fronts. Problem is, the current PZero Assymetrico 265s leave about 1/4" of the inner rim exposed, so I'd like to go a bit wider on the rear (or mount a 265 that fits better than the PZeros). Given that my car is AWD, would I be asking for trouble going with 275/35s? The tires I've looked at are all within 4% of the original diameter and also 4% of the front diameter.

You can use 285s on the rear.....2002+ cars have those on the rear and maintained 225s up front. In fact, the C4S has 225s up front and uses 295s on the rear. Don't sweat it: get the 285s. It's my plan next year and you'll find a ton of drivers use them on their cars in this forum.

FYI....the tolerance should be inside of 3% variance. Go with the 285/30 on the rear. If you go with the 285/30 as a replacement for the 265/35 you will have a variance of 2.3%

Thanks for the input, guys. One concern I have about the 285/30s is they would put the rear slightly lower than the fronts (and lower than the 265/35s. Conversely, the 275/35s would put the rears slightly higher (by the same amount). Seems like the latter would be preferable to the former and would give a little more cushion (presumably at the tradeoff of a slightly softer sidewall).

The diameter is negligable. Here are the diameters of the 3 265/35 25.3 275/35 25.7 285/30 24.7

Hey Dell, that got me thinking about the RoW M030 suspension again since the ride hide would be corrected with that mod after putting on the 285s. Having driven my father's C4S yesterday, would you say that the suspension on the 996S is approximately similar to the RoW upgrade? I didn't find it too hard and in corners the reduced sway and tilt was immediately noticeable.

I would have to say no since the RoW option is available on the C4S as well. All I can say is my car feels now like it should have when it left the factory. Gotta love those USDOT ride height restrictions for new car sales!

That's what's so ridiculous. Instead of mandating that SUVs and Trucks (that are actually DESIGNED for OFF-roading) have lowered bumpers for safety, sport car owners need to have their bumpers set higher. It just doesn't make any sense. The last time I met anyone who off-roaded their SUV had to be in Oregon 3 years ago. Nowadays, off-roading means parking in a gravel lot. Anyway, back on topic, I can't wait to do the RoW upgrade. It's third on the list after exhaust and intake.

I'm glad to hear I can put 285s on my 18.0 X 10.0 rears but can I go with 235s on my 18 X 7.5 on the front? Also how will it affect handling? I'm doing more DEs and I want the max traction available (2001 C2) Thanks, K

You cannot put the 235 on the 7.5 rim only an 8.0 will hold that rubber.

If you are worried about getting too much understeer with the car, then you can let a little air pressure out of the front tires. But, you definitely do not need to go to 235s or 245s on the front to even out the height. Like Dell highlighted above, you are talking about a difference in diameter that is negligible. Moreover, the MY02+ cars all went with the 285/30s on the rear as standard equipment. If you like the look (I definitely prefer it), then go for it. Frankly, it's a requirement, in my opinion, on the rear 10" wheel because the 265 looks a little too skinny.

Is any difference in diameter not a serious issue on a C4? I would have thought that an AWD system would have had real trouble with that.. Keith

I decided against the 275/35s, given the AWD. Even though the diameters were well within 4% of the originals and 4% of the fronts, I decided it wasn't worth the risk. I also decided to stick with 265/35s, rather than go wider. I know the car handles great with 265s and I've never had a problem with too little grip. I went with Bridgestone Potenza RE750s. They are not N-rated, but are highly recommended. One thing I discovered in my research, is that some of the N-rated tires (Michelin PS2s are one example) are not approved for my set-up, since the N-rated fronts are 235s, which are too wide for 7.5 inch wheels. If I had gone with the PS2s, I would have had to put non N-rated 225s on the fronts. It made more sense to me to go with the tire I wanted, rather than worry about the N rating. The other thing I discovered is that even with the approved tires, some of the rears are (slightly) smaller in diameter than the fronts, while others are slightly larger. As I understand it, the important thing for the AWD setup is that there is a slight difference in the front/rear diameters in order for the viscous coupling to work properly.