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[rothwem]

My car is an xDrive model BTW.

I have 17x8.5 wheels on the car right now, and I'm going to put 245/45/17s on it. The rolling diameter is 25.7. I have a spare wheel, its a style 157 with a (rather worn out) OEM runflat 225/45/17 that has a rolling diameter of 25.0.

If I was running 245/45R17s, got a flat, and replaced it with my spare with a 225/45R17 tire, would I mess anything up? If it would mess something up, how long would it take? Rolling diameter difference is ~2%

Since your is AWD, I wouldn't risk it. I'm sure if you search, you'll find the threshold at which owners have found the particular point where the traction control, diff, awd system, etc. start freaking out.

Either way, I wouldn't risk it...just buy a cheap 245/45 to throw on your spare rim. Check craigslist; I'm sure you'll find a used one for a good price.

[rothwem]

Originally Posted by FCobra94

Since your is AWD, I wouldn't risk it. I'm sure if you search, you'll find the threshold at which owners have found the particular point where the traction control, diff, awd system, etc. start freaking out.

Either way, I wouldn't risk it...just buy a cheap 245/45 to throw on your spare rim. Check craigslist; I'm sure you'll find a used one for a good price.

So it looks like I'm going for a 215/50/17 to swap onto the spare. The tire that's on the spare right now is really really sketchy and needs to be replaced anyways.

[rothwem]

Originally Posted by rothwem

So it looks like I'm going for a 215/50/17 to swap onto the spare. The tire that's on the spare right now is really really sketchy and needs to be replaced anyways.

Hmm, so it looks like a 205/55/17 is even better. Its an 8.1" tread width, so it ought to work on my 17x8" spare, and will take up even less room. Diameter is 25.9", 215/50 is 25.5, so they're both 0.8% off.

What do you guys think? Am I nutty to put a 205 on an 8" wide wheel, even if its a spare?

Originally Posted by rothwem

What do you guys think? Am I nutty to put a 205 on an 8" wide wheel, even if its a spare?

Nah, for a spare it should be fine. After a quick google search, there are plenty of 205/40/17, etc. out there on 8" wheels and most hardly look stretched at all. With the tall sidewall that you're proposing, any stretch will be even less apparent.

Good call IMO. That smaller size should definitely save weight, trunk space, etc.