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Discussion Starter #1
Right now I'm doing occasional competition with 235/40/17 on my 17x8 rims. What would you guys think would happen in performance/handling if I were to slap 255/40/17 on the same rim size? The 255's would only weigh 1lb more than the 235's.

I'm trying to get a good idea as to the difference that I'll feel(good or bad) when i take it on the track or do some weekend canyon runs.
 

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IMO it will feel sloppy. too much overhang on the sidewalls (probably not right term.) right now, your tires are already 1.3 inches wider than your wheels. if you go to 255 it would increase to 2 inches wider. This would make for a lot of play in the corners.
 

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Discussion Starter #3
I've heard the term sloppy before.. what do you mean by that?

By outside perspective it seems like thicker tires would provide more grip. Assuming this holds true there would still be too much play in corners?
 

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I've heard the term sloppy before.. what do you mean by that?

By outside perspective it seems like thicker tires would provide more grip. Assuming this holds true there would still be too much play in corners?
RTR (Acura RSX/TSX) is limited to 235 on x8s in USTCC (i think that's the venue) and they use 17x8 RPF1s. I've ran RT615 on 17x8s (RPF1s), but the RTs have a decently stiff sidewall. As long as your tire is good, it shouldn't be an issue. I've ran 235, 225 and 215 on x8s. 215 feels sharper due to the slight stretch.

As for 255, I believe you need at least a x9 for that, or it will be worse than a 235. I've ran 235 R comp, and 245s street tires on x9s. 255s on x9 would need a strong sidewall to avoid rolling over... all the worse on a x8.

EDIT: Just realized you're on star specs. I'd still be concerned with 255 on them. By sloppy, it will just be less responsive. I love the turn in response of a 205 on x9 for the Miata, depowered rack, but I'd get 225 for them in a heartbeat.
 

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visual...
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your tire is gonna look like this with the slanted being where it's joining the wheel. when you go around corners, it's gonna have more flex because of the angle it's already experiencing.

From Wiki: Overly narrow rims in relation to the tire width may cause poor handling as the tire may distort sideways under fast cornering.
 

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Discussion Starter #6
Got ya, thanks for the responses. How about the level of danger? Would I also be in the ally of possibly pinching my tires or blowing them out?
 

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I think the only way to know the answer is to look at the temperature of the tire at various sections as you use it. Like if one portion is hotter than the rest, definitely cause for concern. All the more if you're using this in a timed event. 255 RT615s are pretty square on a x9. I wouldn't try with a x8.

FYI: All my 17" info is from running x7.5, x8, x9, x10 on an RSX. I had the x10 with 255/40, slight stretch , great grip, and were my "show, no go" wheels... but I'm selling them now. S2000s also consistently run 255s and they are Almost Always on At least x9.
 

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Discussion Starter #8
Got ya, I have a good idea of what I need to look for now. Thanks for the responses!
 
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