Wheel Offset Calculation?

[DaCan23]

How is wheel offset calculated? Is it...

(Inside Edge to Hub - Outside Edge to Hub) / 2

or

Inside Edge to Hub - Outside Edge to Hub

[Blitzkrieg Bob]

Takes a while, you'll get a head ache, but it works

[liquidtiger720]

I just failed my calc test

[DaCan23]

Seriously, define the variables plz.

Takes a while, you'll get a head ache, but it works

[Blitzkrieg Bob]

http://www.1010tires.com/WheelOffsetCalculator.asp

[Karl]

But first you need to know what the offset is, right?
Offset is the distance from the centerline of the rim to the wheel mounting surface. So divide the rim width in half, and subtract that from the distance from the mounting surface to the inner edge of the rim. I get that distance by laying a straight edge across the back side of the rim and measuring down to the mounting surface.

[DaCan23]

I think your agreeing w/ my proposed calc 1.

My question was directed at calculating the offset of any given rim by hand, not comparing 2. I was curious if the offset of my new rims was correct regardless of markings.

It says 20, but my measurements were 135mm inside, 100mm outside, so 35mm by 2 is 17.5mm....

But first you need to know what the offset is, right?
Offset is the distance from the centerline of the rim to the wheel mounting surface. So divide the rim width in half, and subtract that from the distance from the mounting surface to the inner edge of the rim. I get that distance by laying a straight edge across the back side of the rim and measuring down to the mounting surface.

[Blitzkrieg Bob]

Look at the diagram from the page and taking you measurements as..

total rim with= 235CM

Mid line @ 117.5

117.5 - 135 = 17.5 or 117.5-100 (this depends on if you north or south of the equator)

I guess 2.5mm is wiggle room.

[zygoteer]

pictures speak lots of words ... see this ...
http://www.bimmer.info/forum/showthread.php?t=22893