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Looking for wheel offset info

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Agreed, just to give you some extra reassurance. Here are some notes, too.


When measuring the width of a wheel, the measurement is taken from the INSIDE of the lips. If you measure from outer lip-outer lip, you will end up with ABOUT 1/2" extra on each side (meaning about 1" wider overall).


Backspacing, however, is the distance between the mounting face (wheel meets hub) to the outside lip of the back. With a 4.5" backspacing, that means you have ABOUT 4" from mounting face to actual width (7" wide on the inside of the barrel).


If your wheel is 7" wide, 0 offset would be 3.5" from mounting face to inner lip, both ways. Since you have 4" from inner lip to mounting face, that means you're ABOUT 1/2" pushed positive.


1/2" is ABOUT 12mm, so your wheels are a 13x7 +12


Once you work through the numbers a few times it makes a ton of sense.

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You have to remember that when you measure BACKSPACING, you measure from the mounting surface to the outside of the lip, not the wheel "width". This is because, for whatever reason, wheel width is measured from the beat seat to bead seat.


Here's a great picture of wheel sizing and measurements:




As you can see, there are a few key measurements.


WIDTH (Located at the bottom) goes from bead to bead.

OFFSET (Located at the top) measures in mm the distance from mounting pad to center line. For example, an 8" wheel would have a centerline of 4". If you move the mounting surface TOWARD the car (away from lip) by 1", you will have about a -25mm offset (1" = 25.4mm). AWAY from the car (toward the lip) by 1" and it will be a +25mm offset.

BACKSPACING (Located top left, just inside the barrel) measures the distance from mounting pad to the INSIDE LIP EDGE. Backspacing measures about 1/2" more inside than the width of a wheel. With Chris' wheels, 15x8 +0, the backspacing is 4.5" because it measures just beyond the "width" of a wheel.


I've been wanting to meet with someone who has a BRE bubble flared sedan, as well as a stock-fender sedan, as well as a roll/pull sedan to figure out the MAXIMUM measurements for a 510 with different types of suspension setups.


If anybody has any questions about size/width/offset, etc, PM me. I'll be happy to fiddle with some numbers!

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