Anyone able to explain stretching?
 

Looking at a temporary situation where appearances aren't an issue but performance and wear is. Shot story is 2 sets of rims, 2 sets of tires (track & road). Road are on stock rims but will be replaced next Spring at which point the track tires will go on the stock rims and the new rims will get a new set of tires. Trying to avoid having to drop another grand or so on tires this year.

Anyway the track tires are 245/40/18 which are a good size for the stock rims. The new wheels are going to be 18x9.5 +45. To put the track tires on those rims there has to be a minimal amount of stretching. My understanding is that the tires are 245mm and the rims are 241mm. I thought that would fit w/o stretching but it seems that you need more clearance so there will be some stretching.

I used this to get the measurements:

http://www.wheelsmaster.com/rt_specs.jsp

I can't find the manufacturer specs for the tires (Hoosier R3S04) as they've been discontinued however the replacement Hoosiers do spec to a rec. wheel width up to 9.5 (http://www.hoosiertire.com/speccat.pdf). So it sounds like I should be able to run fine with these however I've got two concerns that are better placed here then in the Will It Fit thread:

1) Will stretching the tire, even a little, cause issues when it it mounted on the smaller rim next year?

2) How big of an effect with the stretching have on the tire in terms of performance/wear? Since Hoosier appears to state that the width falls into the recommended my understanding is that there should be no performance degregation.

Obviously appearance is not an issue.

The link doesn't seem to work, but a 245/40-18 Hoosier R6 should work fine on the stock 8" rim. The range is 8" - 9.5" for this size.

1) Shouldn't be an issue. It's not uncommon for autocrossers to mount wide tires on narrow stock rims because of rim rule contraints. It also depends if the installer is capable of mounting the tires. These R-compound tires have pretty stiff sidewalls and a smaller rim may give them a hard time, but should be ok in your case.

2) Too many variables to provide a blanket statement that says one size is better than another size on the same rim. A lot of it is course dependent and to some degree driver style. Without timing equipment and repeatable measurements, I wouldn't worry too much about it since it seems you're just doing non-competition type track days with this setup.

Wear will be somewhat different. You'll probably see less wear on the edges of the shoulder with a wider tire on the same rim.

It would seem logical to me that there's more contact patch on a non-stretched tire versus a stretched one. Some would say it's negligible but hey, you asked.

That's true but if you extend past the recommended width the tire is no longer operating as specs and will likely not perform better. More contact doesn't always mean better performance. Not to mention the people doing the tire mount won't like you if you ask 'em to overstretch. :)

But I wasn't really trying to get information regarding performance of my car with a stretched tire. Plenty of info about that here, on tirerack, etc. I'm looking to find out if stretching has any adverse affects on a tire itself. I don't think too many people do what I'm planning - stretching a tire a small amount to fit a wide rim then taking the tire off and mounting it on a smaller rim that won't require stretching. If you've stretched something it seems natural to me that it would be a little off when it gets mounted back on the smaller rim.

Based on reading a ton of stuff about this I think it'll be fine.