Back spacing vs. Offset - TCCoA Forums
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post #1 of 5 (permalink) Old 10-10-2002, 10:01 AM Thread Starter
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Back spacing vs. Offset

I know these can't be the same.

The ford catolog lists the backspacing somewhere around 4"
From looking on this site everyone says the offset is 39 mm.

39 mm is nowhere close to 4 inches.

whats the deal with backspacing vs offset?

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post #2 of 5 (permalink) Old 10-10-2002, 10:15 AM
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This subject had confused me for a great amount of time myself. While I am still not entirely sure of this, the way I understand it is this. The backspacing on a wheel is the distance from the farthest outside point on the lip of the rim, to the surface which the bolts rest to tighten the rim down. Thus you would have your backspacing. Offset I believe is measured from the center of the rim as opposed to the edge. The offset of the rim is the measured distance from an imaginary line running down the center of the rim longitudinally to the surface which the bolts tighten down to attach the rim. I'm not entirely positive on these definitions or if perhaps I have them swapped up or what not. It's just what I can recollect from the cob webs of my spam filled college students brain.
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post #3 of 5 (permalink) Old 10-10-2002, 11:02 AM
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Go to and select "wheels" from the tabs at the top. There is a section named "Wheel Tech" that has everything you could think to ask about wheels. Hope this helps...

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post #4 of 5 (permalink) Old 10-10-2002, 11:37 AM
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offset and backspacing are two different ways of measuring the same thing. i find this sight helpful...

it sounds a lot more complicated than it really is. when you see a car with wire wheel sticking out of the fenders, its commonly referred to as having negative offset wheels, meaning the mounting surface of the wheel is way to far in on the barrel of the wheel. hope this helps a bit.
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post #5 of 5 (permalink) Old 10-10-2002, 11:39 AM Thread Starter
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That pic is worth a thousand words and answers every one of my questions.

thanks again,
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