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wheel sizes and offsets....please explain


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#1 AbsoluteGTR

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Posted May 08, 2007 - 01:25 PM

There are two thing that I have never really understood. For example

235/35/18

I know 235 is the diameter of the tire, correct? 235millimeters, correct?

What is 35?

And obviously 18 is the diameter of the wheel....

And my last question is....Can someone please explain offset? I just dont get it? (35mm offset, etc.)
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#2 shadowless

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Posted May 08, 2007 - 02:19 PM

There are two thing that I have never really understood. For example

235/35/18

I know 235 is the diameter of the tire, correct? 235millimeters, correct?

What is 35?

And obviously 18 is the diameter of the wheel....

And my last question is....Can someone please explain offset? I just dont get it? (35mm offset, etc.)


235 is the section width. this follows the letter or letters identifying the type of vehicle or service for which the tire was made. section width is the cross section in millimeters. and as you may know, 25.4mm = 1 inch

more specifically, the cross section is the distance measured from the widest point of its outer sidewall to the widest point of the inner sidewall when mounted and measured on a specific wheel width.

the 35 is the sidewall aspect ratio. in your example, 35 means that the sidewall height (rim to tread) is 35% of the section width (235 in your example). it is also called section height, tire series, tire profile, or just aspect ratio.

now, offset of a wheel is the distance from its centerline to the hub mounting surface. there are 3 types of offset- zero, positive, and negative.

zero offset means that the hub mounting suface is even (from an anterior to posterior aspect or posterior to anterior aspect) with the wheel's centerline.

positive offset means that the hub mounting surface is toward the front or side of the wheel.

negative offset means that the hub mounting surface is toward the back or brake side of the centerline. some deep dish wheels have this.

most wheels you ever will deal with have positive offset.

to simplify offset, +32mm offset is more aggressive than +35mm offset-i.e. the same wheel with +32mm offset will stick out farther (laterally) than a +35mm offset of the same wheel. you cannot directly compare one wheel with +x offset and another wheel with the same +x offset in terms of how close to the fender they will sit. this is even if they are the same diameter and width. furthermore, because wheel A of +x offset clears a certain brake caliper does not mean that wheel B (again of the same diameter and width) with the same +x offset will clear.

hth

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vf-engineering stage 2 SC, kreis-sieg exhaust, 3.91s, BBS LMs wrapped in F1s, alcon bbk, and a few other goodies....
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#3 offroader1006

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Posted May 08, 2007 - 04:07 PM

yeah, thats pretty much it.

should sticky this in the wheel forum

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#4 Turd Ferguson

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Posted May 08, 2007 - 05:30 PM

Couldn't have said it better SG! ;)
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#5 AbsoluteGTR

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Posted May 08, 2007 - 10:42 PM

Thanks, I get it now.

Just one last question: Is there a way to measure what offset you might need in order for the wheel to line right up to the fender?
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#6 shadowless

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Posted May 08, 2007 - 10:57 PM

Couldn't have said it better SG! ;)


that is what i am here for :)

i am glad you approve of my reply. :)

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06 M3 silver gray on black, SMG, premium, cold weather, HK, xenons, 19" double spoked wheels
vf-engineering stage 2 SC, kreis-sieg exhaust, 3.91s, BBS LMs wrapped in F1s, alcon bbk, and a few other goodies....
07 X3 3.0si monaco blue on gray (hers), 45% suntek carbon tint on front side windows


#7 shadowless

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Posted May 08, 2007 - 11:02 PM

Thanks, I get it now.

Just one last question: Is there a way to measure what offset you might need in order for the wheel to line right up to the fender?


it is pretty tough to do that but not impossible.

what wheel are you looking to get?

if it is a custom wheel, then the wheel's manufacturer should know exactly what offset you need for whatever application (in this case, lining right up with the fender).

btw, you normally do not want the wheel to line up right to the fender. this does not allow much if any lowering (i.e. your tires will rub and possibly pop out the bottom edge of your fenders). also, depending what tire you run, you could rub even at stock height.

well, back to measuring what offset you are looking for:

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you are gonna have to take careful measurement using the above.

or you can do a search on audiworld and other forums to see if someone is running the wheel you are looking for.

again, hth

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06 M3 silver gray on black, SMG, premium, cold weather, HK, xenons, 19" double spoked wheels
vf-engineering stage 2 SC, kreis-sieg exhaust, 3.91s, BBS LMs wrapped in F1s, alcon bbk, and a few other goodies....
07 X3 3.0si monaco blue on gray (hers), 45% suntek carbon tint on front side windows


#8 AbsoluteGTR

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Posted May 09, 2007 - 10:01 AM

The rims I am looking at getting (in a few months) will either be 18" or 19" Velocity Motorsport RS4 reps. I know that they already have enough offset to bring it fairly close to the fender.

I was just inquiring for future knowledge!

BTW....what do you all recommend? 18" or 19"

I really want 19" but 18" seem more practical...
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#9 travsm3

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Posted May 09, 2007 - 12:53 PM

19's IMO.
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#10 PrzFghtrNfrno

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Posted May 09, 2007 - 03:31 PM

If you get 18's you'll regret it.

19's fo sho...do it.
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#11 AbsoluteGTR

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Posted May 09, 2007 - 11:10 PM

DO IT....lmfao.....good times good stuff....

I just dont want to sacrafice comfort for one extra inch.....plus the added road noises...
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#12 W204Guy

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Posted November 29, 2010 - 07:51 PM

I just dont want to sacrifice comfort for one extra inch


That's what she said......

Good luck with the wheels. Nice car by the way.

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