What is the widest tire that will safley site the stock 18" performance wheels? I currently have the pilot 245/45/18 Rear and 225/45/18 front.
I would like to keep the stock wheels, just add more meat in the rear, the local Discount Tire store said I could put 275/40/18 rear and 245/40/18 front to keep the ratio right.
I am just curious if a 275 is safe on the stock 18 x 8 wheel?

<font color=black>2003 G35 Coupe, Blk/Blk</font color=black>
<font color=red>Frisco, TX</font color=red>
ChrisBruceLoans.com

You'll get some people who will say yes, but the answer is no. All the tire manufacturers recommend against this. You'll have severe tire bulge. You can fit 245/40s to the front, the widest I would go in the rear with stock wheels is 255/45/18. This setup will handle well (better than stock) and wont upset the VDC. It will get rid of a lot of the understeer.

I think the logic of understeer reduction is that the difference between front and rear width stock is 20 (225F and 245R) and with the suggested tire size change the difference between front and rear width is reduced to 10 (245F and 255R), and thus his conclusion. If only the rear was changed to be wider, then the understeer condition would be worsened as you mention.

Cpe 6MT/Aero/Prem/ATI/RT cats/Borla hdrs-catbcks/Nismo flywhl-cltch/TS-ECU/Tein flex EDFC/Stillen sways

No. Way too big. 245 is the larges size recommended for an 8" wheel. 275 is even too big for an 8.5" wheel.

'03.5 Brilliant Silver AT Sedan, Premium, Aero Kit/Package, Sport, Winter, Stillen Air Box, Z pipe, Clear Corners, Alum. Pedals, Polk Tweeters, Clifford RSX 3.5, Gram Light 57F Pro's (on the way!)

How about a 8.5 ? Can 255 fit in the rear?

keep in mind that the car is setup to understeer from the factory. This means tires, springs, shocks, sways, and camber are all biased to make the car understeer. Changing the tires is just one piece of the puzzle.

I just autocrossed my coupe today and it was understeering like crazy and wore down the corners of the front tires by a noticeable amount. I definitely want more neutral handling but I don't want to 'waste' two front tires w/ 4300 miles on them by switching to 245's up front. Maybe I'll check out a rear sway bar...

255s will go on 8's or 8.5's. Once you want to go to 255 you need 9's. 9's will take you to 275.

The only problem i see is that it's hard to find a wheel that's within stock radius. 255/40 gets you 2.7% too slow and 255/35 gets you 1.1% too fast. Which would be the best size if i have 245/40's in the front? Is there a difference in look between 245 and 255? I want a wider look.

Ray

If 255/40's are too slow, then how can 255/35's be too fast? That's actually a smaller overall diameter. You can run 255/45 and in the rears and be fine. You'll be exactly at 27" which is within the 26" +/- 0.3" <-- (should be 26.8" +/- 0.3" my bad...) wiggle room you have. With fronts at 245/40 you'll be at 25.7" in the front and 27" in the back giving you a stagger of 1.3". The stock stagger is 1" so you're fine.

Yes 255's will look wider but not by much. On a 245 the amount of tread actually in contact with the road is about 210mm wide. With a 255 it will likely be about 220mm.

But as for going beyond 255 on an 8", you can do it, but you will be go against mfr guidelines and void any tire warranty.

I was comparing the new sizes to a stock sedan size. That's why the numbers didn't seem right.

will a 225 45 18 front and a 255 45 18 rear ,(OEM rims)work together without causing VDC issues

I don't know the exact specs, but it does seem unreasonable to try and stick such large tires on a wheel designed for alot smaller. It just seems unsafe. Obviously drop the money for a dedicated wheel for that size. Don't cheap out on a crucial part imo.

On the side note maybe change up how your driving the g. If you watch the video on amazon about the z cars, he talks of how the pro driver for the vid talking about a different driving style is needed to whip the car around fast. Cuz normal techniques aren't gonna work on the car to whip it around the corner without a bit of understeer. Its there so people dont kill themselves on accident from spinning out. But better than excessive oversteer and smashing a wall or other barrier.