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      01-24-2019, 11:25 PM   #1
Sirrith
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Wheel offset questions

Hi all, I'm planning to change my stock 17" rims to 18" 8.5 in the front and 9.5 in the back. I asked in another forum about offsets and one guy said he is using ET38 in front, on an 8.5j rim because that way the outer edge remains in virtually the same position as the stock ET29 rim.

That got me thinking. Originally my plan was to keep to the stock offsets of ET29 front and ET40 rear as much as possible, so that the extra width would be evenly distributed, but is this the wrong way to approach it? Should I be getting higher offsets instead so the outer edge doesn't stick out too much? At what point will the tyres start rubbing on things they shouldn't?

Thanks!
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      01-25-2019, 12:00 AM   #2
Bob20124
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I just up-sized from 17"'s to the following: Fronts 8.5x18 ET 30 with 245x40x18 PS4s. rears 9.5x18 ET 35 with 275x35x18 PS4s. Need to compare to what is on the car now.

One site to look at. Lets you compare side by side.
https://www.wheel-size.com/calc/
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Last edited by Bob20124; 01-25-2019 at 11:43 AM.. Reason: attached picture
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      01-26-2019, 06:44 AM   #3
Sirrith
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Thank you Bob. Have you done anything to the suspension or is yours stock? I popped by a wheel/tyre shop today, and the guy swore that the maximum width rears I could fit in a z4 was 9", not 9.5" unless the suspension was modified or there was some form of camber.

He also suggested ET36 8.5" fronts and ET50 9" rears. Wouldn't ET50 be too much?

edit: I found some Rota Grids online in thefollowing sizes: 18x8.5 ET30 front and 18x9.5 ET35 rear. Does this seem like a good fit? Bob's photo has the same measurements and they look OK to me, though I can't see if they're sticking out or sunken in from this angle.

Last edited by Sirrith; 01-26-2019 at 07:20 AM..
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      01-26-2019, 07:01 AM   #4
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I'm stock non adaptive suspension. Another reference: https://www.e90post.com/forums/forumdisplay.php?f=12 The lower the ET further out. higher closer in. ET 50 may be too close to suspension. a lot of folks go with ET 35 all around.
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      01-26-2019, 08:27 AM   #5
Sirrith
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Thanks, yes, I think ET 30 and ET 35 are safe bets.

Now to choose a style/colour/brand...

Does anyone know what colour these Volks are? It's hard to tell from the photo. They look bronze-ish, but at the same time not really... (not my photo, just found online)
http://hawknpoke.com/wp-content/uploads/z4volk-08.jpg
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      01-26-2019, 08:38 AM   #6
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Pulled cover of hibernating car. Both front and rears are still slightly recessed inside fender.
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      01-26-2019, 09:01 AM   #7
Sirrith
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Thank you so much Bob, really appreciate the help.
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      01-28-2019, 10:09 AM   #8
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The correct answer is to use a 35mm offset on the front wheels as it reduces king pin offset of 9.6mm on the stock 29mm offset factory wheel. It also allows you to run an 18x8.5" rim and still fit up to 255/35 or 30 tires without hitting shock strut.
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      01-29-2019, 06:47 PM   #9
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Thank you, I just ordered a set of 18" rims in 8.5 and 9.5 35ET.
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