From digest.v7.n519 Fri Oct 31 06:39:36 1997
From: Lowell Seaton <SEATON.LOWELL_at_EPAMAIL.EPA.GOV>
Date: Fri, 31 Oct 1997 00:40:43 -0500
Subject: Wheel Offset
In v7 #515 somebody asks about wheel offset. The poster has a 6
series and he wants to put larger, wider wheels on it while keeping the
stock look. Figuring wheel offsets gets real confusing real quick.
First you should find out what your current wheel offset is. At least on
my BMW wheels, you can find this real easy. Just take one of your
wheels off and look on the inside. You should see a BMW part number
and a number that begins with "et". You should also be able to tell how
wide your rims are. Hopefully your rim width is stamped in the rim.
I am going to guess that you probably have about 25 mm offset rims and
your rims are 6.5 inches wide. So if you want to put 8.5 inch rims on
and not have the tire stick out any more than stock, then you have got to
pull the rim inside the wheel well. The rim is 2 inches wider so that
means it is going to stick out of the wheel well 1 inch more than before,
keeping the same offset.
But if you don't want the tire to stick out more, you have got to increase
the offset by 1 inch or 25.4 mm. This will give you a new offset of about
50 mm. This was a long winded way of describing how to change rim
widths and keep the outside rim edge even with the original wheel. The
mathematical formula is:
[(new rim width in inches - old rim width in inches) / 2 * 25.4] + old offset
in millimeters = new offset in millimeters
The next question is do you really want to do this? Do you have 2+
inches of clearance on the inside of the tire? Will the tire rub on the
struts, inside wheel well, muffler, etc? I doubt if you will be able to
completely tuck the wider wheels inside the car without something
I also doubt if you will have much chose of offsets for you new rims.
Unless you are buying very expensive, custom made 3 piece rims, I think
most aftermarket rims are going to have about 35 mm of offset. This
should work OK for you. The tire will stick out of the wheel well a little
bit more than stock but you won't have a problem with rubbing on the
The key to remember is: Increase the offset to keep more of the wheel
tucked inside the car. Good luck.
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