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Wheel Sizing **Important Question**

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Old 08-29-2018, 12:38 AM
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Wheel Sizing **Important Question**

Hey everyone, i have a very specific question about tire size with a certain size of rim, i have 2003 wrx, i bought some 18x8.5 wheels and got some 245/40zr18 tires for them, but had to return the rims becuase of worng bolt pattern they sent me.

Here is the important part, they said that they dont have the bolt pattern i need with the 18x8.5 rims, but they have the bolt pattern i need but with the same rims except they are 18x9.5,

Now, the big question being since i already bought the exact tires i needed which are 245/40zr18, will those tires work for the 9.5 rims? or is that size of tire only for an 8.5 rim? or does it not matter? can i run that tire size with 18x9.5 rims?

Please let me know as i am having a difficult time with this, thank you very much
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Old 08-29-2018, 08:42 AM
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A 9.5" is at they very upper end of what is generally accepted to be "safe" wheel width range for a 245/40. Sure, there are those out there that will say, "Pfft. I stretched a 205/50 onto a 10" and ran it for years blah blah blah." Can you run bare back on the village bicycle? Sure. Is it safe? Not at all.

An additional factor to consider here is the wheel offset. Totally guessing here, but I'm willing to venture the 18" x 8.5" wheels you were wanting are in the mid to low 40 mm offset area. Let's go conservative and say +44 mm. I am also willing to venture the 18" x 9.5" wheels you are being offered are in the mid to high 30 mm offset range. Again, conservatively, I'll guess +35 mm. If the math is overwhelming, you can use this site, but you are looking at close to a whole inch additional outboard width (poke) going with the 9.5" wheels, assuming that those are the offsets. You're wandering into areas where fitment may.. will.. be an issue.

TL;DR -- if you're keeping the tires, I would find another wheel in 18" x 8.5" or buy from somewhere else that has the wheel I do want in 18" x 8.5".
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Old 08-29-2018, 12:39 PM
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thank you for the quick reply, that was my bad for niot including the offset in there.

So, the 18x8.5 are 30mm and the 18x9.5 are 34mm, is that gunna make a big difference with what you had said or not really? and am i gunna have to have some gnarley tire strech to make this setup work? or can i make it work without alot of tire stretch. not that i care too much about that i like the look of it alot, but im going for a little bit more on the performance side than the low and slow side, so i wasnt to be able to do pulls and go up mountain roads, and some day the track.
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Old 08-29-2018, 01:39 PM
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A 245 tire should sit fairly square to the lip on a 9.5" wheel. A wider wheel or narrower tire wouldn't really be recommended. Unless you're going for "that look", a general rule of thumb is to not have a wheel width wider than the tread width of the tire you're mounting on it.
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Old 08-29-2018, 02:31 PM
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What tires do you have?

Check the specs for the tire. There's specifications for the measured rim width as well as the range.
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