I know about backspacing- how far away the center section of the wheel is from the edge of the outer section. But what the heck is offset? Nobody's been able to explain that to me yet- they always talk about backspacing. (grins) Then, I ask them "Isn't that backspacing?", and they get confused... Thanks! ------------------ -Tom P (Hot rodded 1986 Firebird 2.8l) from http://www.f-body.net/mailbag/3rd/3rd_mailbag.html message boards ---Think your car could be pic of the week? Visit http://www.f-body.net for details!

Offset is how far out or in the centerline of the tire or rim is from the mounting surface of the hub.

Take those ghetto Hondas with the spoked rims that stick waaaay out from underneath the car. Those rims would have very little backspacing, placing the rim outside the fenderwell. The centerline of the rim is a good distance from the mounting pad. That's known as HPO or high positive offset.

Isn't that backspacing?



If I understand that right... A high offset is the same as low backspacing? Why bother talking about offset, then? Why not just leave it all in terms of backspacing?

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-Tom P (Hot rodded 1986 Firebird 2.8l) from http://www.f-body.net/mailbag/3rd/3rd_mailbag.html message boards
---Think your car could be pic of the week? Visit http://www.f-body.net for details!

Backspacing is the depth of the rim from the mounting surface to the inside edge of the rim.

Offset is the distance the mounting surface is from the CENTER of the rim. Lets say your rim is 8" wide, the center line will be at 4". The offset will be measured from this line to the mounting surface (the flat area that goes agains your drum or rotor when you put the rim on your car). If this surface is on the inside of the center line, you have negative offset, if it is on the outside it has a positive offset.

Hope that clarifies it..


Ken

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Some 8" wheels mount the beads at 8", but actual width of the wheel from the outer edge to outer edge may be 8.5" to account for the thickness of the lip. In this case a wheel with zero offset would have 4.25" (8.5" actual width divided by 2) backspacing. I usually see offset measered in millimeters and backspacing in inches. The offset measurement is sometimes more useful because you don't have to know the actual width of the rim to know the exact position of the wheel.