backspacing question
Race Director
Joined: May 2000
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Re: backspacing question (70 LS1)
Offset is the distance from the "center plane" of the wheel (the center plane between the rim beads) to the mounting plane.
You can measure offset with reasonable accuracy by laying the wheel on a flat surface - outside face down - and placing a length of 2 x 4 across the inside rim edge. Measure the overall width of the wheel from the surface to the bottom of the 2 x 4 and call it "A".
Now measure the distance from the bottom of the 2 x 4 to the wheel mounting plane and call this "B".
Offset = A/2 - B. This formula will give the correct algebraic sign.
If you have eight inch Rally Wheels you should measure an offset of -0.5".
If a tire is mounted just measure the overall width of the tire on the wheel and use this as the "A" dimension. Measure "B" from the inside sidewall of the tire to the wheel mounting plane. The result should be the same.
Duke
[Modified by SWCDuke, 10:11 AM 4/28/2002]
You can measure offset with reasonable accuracy by laying the wheel on a flat surface - outside face down - and placing a length of 2 x 4 across the inside rim edge. Measure the overall width of the wheel from the surface to the bottom of the 2 x 4 and call it "A".
Now measure the distance from the bottom of the 2 x 4 to the wheel mounting plane and call this "B".
Offset = A/2 - B. This formula will give the correct algebraic sign.
If you have eight inch Rally Wheels you should measure an offset of -0.5".
If a tire is mounted just measure the overall width of the tire on the wheel and use this as the "A" dimension. Measure "B" from the inside sidewall of the tire to the wheel mounting plane. The result should be the same.
Duke
[Modified by SWCDuke, 10:11 AM 4/28/2002]
Race Director
Joined: May 2000
Posts: 12,712
Likes: 2,264
Re: backspacing question (dennis)
It will likely be a bit more. Backspacing is measured from the inside face of the wheel, not the bead flange. The wheels are called "eight inch" because this is the distance of the bead mounting flanges, but the overall width of the wheel is measured between the outside faces, so you have to add the width of the flanges.
I prefer to work with the offset dimension because wheels with different flange thickness can be directly compared. If you work with backspacing, it's apples and oranges unless the flange thicknesses are the same.
Duke
I prefer to work with the offset dimension because wheels with different flange thickness can be directly compared. If you work with backspacing, it's apples and oranges unless the flange thicknesses are the same.
Duke
