Join Date: Feb 2001
Location: socialist lib heaven mASS
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Re: wheel offset vs. backspacing???
3.75" backspacing on a 7" wheel has to equal .25" offset, right? If the backspacing were' 3.5" then the wheel center would be in the center of the rim, yes? So if you move the center of the wheel outwards .25 inches you will have 3.75" backspacing. If you bolt this wheel to a 1" spacer on the hub you could say that you then had 2.75" backspacing on the wheel (if you consider the spacer to be part of the wheel) in in that process it would have changed the offset from +.25" to -.75" (or the other way around, I dunno which is pos or neg offset)
Does that help? I'm not an expert on this, in fact I never even thought about it before, but it's just simple math once you wrap your head around the parts involved.
On the other hand, if they need to know what the offset is to give you the spacers, just make something up. A one inch spacer is a one inch spacer.
Another way to look at it is this: to get the front surface of a 7" rim to be aligned with the front surface of a 5.5 on the same truck, you need to compensate by .75" more backspacing. If you then add in the 1" spacer, you would need to compensate for that as well by adding a total of 1.75 more backspacing or 5.5" backspacing. I dont think 7" rims come in 5.5" BS, which would have to be 2" offset.
someone check my math please? I know there's engineering types in here and I didnt even go to college.