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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Technical Forums > Wheels and Tires Forum Sponsored by The Tire Rack > Tire vs Rim Width Ranges - How do YOU pick?!



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      12-07-2012, 10:07 AM   #1
BmerMeUp
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Tire vs Rim Width Ranges - How do YOU pick?!

Hi. So I think I understand the concept of "stretching" a tire and the risks of putting a too-wide tire on a too-thin rim, but even the calculators I am reviewing give a rim width "Range" for a given tire ratio. Offsets are still an entirely different problem for me, I know what it means, but have NO idea how one would really look compared to another or how that affects my track?!

For example, 235/35/19 says it can go on a rim width of 8 - 9.5 in. That's sort of a big range! Many here have that and call it staggered! So which is it - 8 or 9.5? I found a reference which suggests for every 0.5" of rim width the same sized tire will change in height by 0.2" (Tire Rack Calculator doesn't confirm this however?) so that gives me some idea at least.

But I'm trying to understand how to pick a properly sized tire which isn't stretched, won't rub, and will just "look good," nice and flush with a vertical sidewall. I'm not big on the "mushroom" effect when the tire is too wide for the rim nor do I want (although on some it looks good) the "stretched" look when it's the other way. All I know is I need an 18" rim on a 2008 E91 328xi due to road conditions here - still on the fence for staggered vs. square, and this "rim width range" bit isn't helping!

Arg. Thoughts?
How do you decide what rim and tire widths you think you want and know will fit?
And shouldn't offset-to-flush be a fixed number for a given chassis, based on the width of the rim?

Or MAYBE... Maybe I should just call Gary when I'm ready and give him my Visa number and wait for something nice to arrive at my doorstep?? Ha.
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      12-07-2012, 10:41 AM   #2
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Just pick which rims you like, then call a vendor or reseller and ask what setups work for your car. They can tell you what sizes/widths/offsets work best and which tires will fit.
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      12-07-2012, 11:24 AM   #3
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You may be over thinking this. Your choices for 18" aren't that numerous. If you're staggering on an XI, you have one ideal choice for 18" tire sizing : 225/40R18 front and 255/35R18 rear. As long as the rim is 7.5"-8.5" front and 8.5"-9.5" rear you'll be in the correct range.

If you're not staggering, just use 225/40R18 all around with wheels that are 7.5"-8.5". The vast majority will be 8" wide.
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      12-10-2012, 11:35 PM   #4
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Quote:
Originally Posted by Gary@TireRack View Post
You may be over thinking this. ...
I'm *certain* I'm over-thinking this! Ha.
I just didn't really know what to think, was mostly the problem.
It's not like a suit I can just try on and decide though, it's expensive and I want it to work out "first try" - so THANK YOU Gary, as I hoped you might, for clearing through the muck. I didn't realize 18's made my life less complicated, which is a good thing. I will hold on to your suggestions as spring draws closer, when another run to the border to pick up my Tire Rack order will become necessary!

Patrick, thank you also for the suggestion - that was what I was leaning towards also.

Thanks guys.
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      12-11-2012, 07:45 PM   #5
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Not to add to the confusion but here is an example that may help you:

18x8.5 - 235/40/18 - Good size fit, no 'mushroom', no stretch
18x8.5 - 225/40/18 - Still a good fit, but it'll look slightly stretched since it's narrower by 10mm compared to the 235 width.

Also note that different brands have different shoulders which may look different even with the same size. IE: Yokohama S-drives will appear to be wider than say, a Hankook V12.

Check http://tyrestretch.com/ if you'd like to see different tire sizes on different rim widths.
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      12-11-2012, 07:58 PM   #6
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A good rule of thumb is to look up the tread width of the tire size that you're considering e.g. a 225/40-18 - now you'd *think* that it would be 225mm but that's actually the "Section Width" which is the overall width of the tire at the widest point when mounted on a specific rim which the tire mfgr. usually lists in their specs

if you go here and click on specs

http://www.tirerack.com/tires/tires....eMake=Michelin

you will see that that size of a PSS has a tread width of 8.2" so it will probably look/ride/handle best on a 18x8 or 18x8.5 rim (that is, close to the width of the tread.) A wider rim will look stretched; a narrower rim will make it look pinched a little like someone who put 60's on their old musclecar's stock rims. A 235 is exactly 8.5" wide tread width so that would be a darn near perfect fit on a 8.5" wide rim (which is what the previous poster said, just in a different way.)
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      12-11-2012, 09:57 PM   #7
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Last edited by Vigorous; 12-13-2012 at 10:36 AM. Reason: mistake
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      12-15-2012, 12:38 AM   #8
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Quote:
Originally Posted by VMRWheels View Post
...
Check http://tyrestretch.com/ if you'd like to see different tire sizes on different rim widths.
Wow. Whoever made that library was obsessively dedicated. Thanks for that link. That does help immensely to visualize the effect!

Quote:
Originally Posted by N8N View Post
... but that's actually the "Section Width" which is the overall width of the tire at the widest point when mounted on a specific rim which the tire mfgr. usually lists in their specs

if you go here and click on specs

http://www.tirerack.com/tires/tires....eMake=Michelin

you will see that that size of a PSS has a tread width of 8.2" so it will probably look/ride/handle best on a 18x8 or 18x8.5 rim (that is, close to the width of the tread.) A wider rim will look stretched; a narrower rim will make it look pinched a little like someone who put 60's on their old musclecar's stock rims. A 235 is exactly 8.5" wide tread width so that would be a darn near perfect fit on a 8.5" wide rim (which is what the previous poster said, just in a different way.)
I also did not know that - treads are measured based on a specific rim.
Thanks again, very helpful!

Sorry for the late reply guys, got sidetracked and luckily found this thread with your replies again.

Thanks!
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      12-15-2012, 06:06 AM   #9
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Quote:
Originally Posted by BmerMeUp View Post
Wow. Whoever made that library was obsessively dedicated. Thanks for that link. That does help immensely to visualize the effect!



I also did not know that - treads are measured based on a specific rim.
Thanks again, very helpful!

Sorry for the late reply guys, got sidetracked and luckily found this thread with your replies again.

Thanks!

You can consider running 245 square on 8.5 or 9.0 wheel without issues and have ability to rotate tires also.
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      12-26-2012, 09:24 AM   #10
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Quote:
Originally Posted by NokTurNaL 330i View Post
You can consider running 245 square on 8.5 or 9.0 wheel without issues and have ability to rotate tires also.
Thanks!
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