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Heres an idea 18 x 8.5 42 mm offset in a BMW application. Would it fit or is the center bore all messed up between the cars. And then what tire size? Could you go an 18 x 9 in the back with a 42mm offset? Ideas suggestions.
 

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PhantomGTO said:
Heres an idea 18 x 8.5 42 mm offset in a BMW application. Would it fit or is the center bore all messed up between the cars. And then what tire size? Could you go an 18 x 9 in the back with a 42mm offset? Ideas suggestions.
8.5 w/42mm up front is pushing it. 8.5 w/42mm in the rears should fit fine. 9's w/42mm will need a bit of fender rolling. Centerbore on the BMW rims should work ok, though might need a centering ring.

Here's a fitment guide that seems pretty accurate:

NEW BOLT PATTERN FOR GENERAL MOTORS 5-120!!!!!!!!!!
GTO IS ACTUALLY A HOLDEN MONARO FROM AUSTRALIA



WIDTH..........OFFSET............WIDTH OF TIRE
7.0...............+26/+65.............215/225/235
7.5...............+33/+61.............215/225/235/245
8.0...............+39/+55..............225/235/245
8.5..............+45/+48..............235/245/255
9.0.(MAX).........+48................245/255
REAR ONLY
8.0................+36/+65.............245/255
8.5................+42/+65...............245/255
9.0.................+48/+65...............255/265/275
9.5................+55/+64...............265/275/285

OFFSETS GREATER THAN SHOWN ABOVE WILL RUB ON REAR
FENDER LIP. (25MM FENDER LIP)
Padre
 

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Oh my f*ck!
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BMW wheels will definitely need a centering ring - they are a 72.6 (I think) mm bore, ours is a 69 something (something odd and uncommon, of course).
 

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MBM/M6
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PadreGTO said:
8.5 w/42mm up front is pushing it. 8.5 w/42mm in the rears should fit fine. 9's w/42mm will need a bit of fender rolling. Centerbore on the BMW rims should work ok, though might need a centering ring.

Here's a fitment guide that seems pretty accurate:



Padre
I must be a dope or something, but I can't seem to make sense of the table you posted. I've seen it before and tried to understand it, but to no avail. Can you (or anyone) query their decoder ring and post a deciphered version?

I'm looking for something broken down by rim width and associated tire size. Something like:

FRONT OFFSET TIRE SIZE
18 x 8 48mm 245/45
18 x 8 51mm 255/45
18 x 9 ???? 2xx/xx
19 x 8 ???? 2xx/xx
19 x 9 ???? 2xx/xx

REAR OFFSET TIRE SIZE
18 x 8 ???? 2xx/xx
18 x 8.5 ???? 2xx/xx
18 x 9 ???? 2xx/xx
18 x 9.5 ???? 2xx/xx
19 x 8 ???? 2xx/xx
19 x 8.5 ???? 2xx/xx
19 x 9 ???? 2xx/xx
19 x 9.5 ???? 2xx/xx

What I'm trying to determine (even before I get the dang car) is what tire/rim combination works together. For instance, if I want to put a 275/30 on a 19 x 9 rim, what does the offset need to be? Or a 255/45 on a 18 x 8? I think you get my drift.

I appreciate your help.
 

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2K5 GTO said:
What I'm trying to determine (even before I get the dang car) is what tire/rim combination works together. For instance, if I want to put a 275/30 on a 19 x 9 rim, what does the offset need to be? Or a 255/45 on a 18 x 8? I think you get my drift.

I appreciate your help.
In the table I posted, the "OFFSET" column gives you the range of offsets that fit for that size. So anything within that range will fit.

The fronts are pretty strict about this, because I don't think you can roll the front fenders.

But the rears allow even more room.

So you can go outside of the offsets on the rears if you roll the fenders. E.g. my rears are 19x9.5 with 265/30 tires and a 45mm offset. They rubbed, but fit fine after the fender rolling.

Fender rolling might buy you around 5-10mm, but not likely more. E.g. unrolled, a 48mm offset 9" rim might fit; rolled a 40mm offset 9" rim might fit.

But don't sue me. :) A lot of this is hit and miss, and you also have to deal with the fact that some tires with certain ratings are wider/narrower than the rating.

Hope this helps. Cliff notes: try to stay within the ranges listed on the table and you should be ok.

Padre
 

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Thanks, Padre. I appreciate the reply.

I'll use the table as a guide and, depending on the manufacturing variance between vehicles, try and find the appropriate rim width and offset for my particular car when the time comes.

This is all pretty new to me. I'm used to 60's muscle cars (I just sold my '69 Chevelle SS396 so I'd have the money for a GTO). The '69 had a huge rear wheel well (15 x 10 with 275/50 fit the rear with a mile of room left, 15 x 8 on the front with 245/45 and plenty of room left there too.)

Metric cars, wheel offsets, hub-centering rings... I'm tired now. (No pun intended.)
 
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