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Old 07-08-2004, 09:15 PM
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Help me understand wheel offset!

I recently took the rims off my Nova and layed a steel ruler across the back edge of the rim and measured to the rear where the rim meets the drum, it measured 4 1/2". I want to set my tires back by 1/2", so do I add the 1/2" to my reading and need a 5" offset?

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Old 07-08-2004, 09:52 PM
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Rim offset if related to the distance the mounting flange is from the physical center of the rim, if the flange is centered in the rim it is called zero offset. If you wanted to move that position 1 inch farther out to move more tire under the car you would call that +1 (positive) offset. Do not confuse offset with backspacing, back spacing takes into account the rim lip thickness. The lip thickness is added onto the offset to give you a rims "backspacing".

A good example is front wheel drive vehicles, they have a lot of positive offset built into the rim.
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Old 07-08-2004, 10:27 PM
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Graphical explanation:

Wheel offsets:


backspace:


Wheel Lug PCD:


Wheel Terminology:
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Old 07-09-2004, 10:26 AM
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http://www.rsracing.com/tech-wheel.html <~~~info site that Tim used.....joe
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Old 07-09-2004, 10:40 AM
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Re: Help me understand wheel offset!

Quote:
Originally posted by jsdailey
I recently took the rims off my Nova and layed a steel ruler across the back edge of the rim and measured to the rear where the rim meets the drum, it measured 4 1/2". I want to set my tires back by 1/2", so do I add the 1/2" to my reading and need a 5" offset?
You are describing backspacing, which is different from offset. As described above, backspacing is a measurement relative to the inboard edge of the wheel, offset is relative to the wheel centerline.

What are you looking for in unambiguous terms? Are you looking for the tires to move inboard, i.e. less track width? For this you would increase your backspacing.
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Old 07-09-2004, 11:01 AM
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^^^
Correct. If you want to increase backspace, but not change offset, then you would need to increase overall width of the rim.
So for example, if you have a 7 inch wide rim, with 4.5 inch backspacing, and you want to keep the outer lip the same (not change offset), then you would buy a 7.5 inch rim with a 5 inch backspacing. If you want to bring the entire rim inboard (if the rim sticks out the fenders too much), then you would buy a 7 inch wide rim with a 5 inch backspacing.
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Old 07-09-2004, 09:30 PM
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i dont know much about wheel offset, but these guys sound like they know what there talking about

coolness
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