So I am trying to calculate the backspace for my wheels. Can someone tell me if I am doing this correctly:

Offset = Backspace - (Rim Width/2)

38mm = X - (8.5/2)
1.496" = X - 4.25
5.746" = X

These calcs show 5.746" of backspace. The wheels I have are the 20x8.5 Roush wheels and they show an offset of 38mm. I just ordered a 2" Autosping front leveling kit and I want to put 35x12.50 Toyo M/T's on my truck (05 Screw 4x4). Will I have any problems with this set up or should I go with the 33x12.50? Thanks for all your help.

 

Bump....Anybody?

 

It might be a little tight with only a 2" as and the large lugs of the M/T tires. Rim and backspace should be no problem just don't know how much clearence you will have with the upper A arms.

 

Check out the chart on this webpage. According to the chart, 38mm offset on an 8.5" wheel, is a little over 6" of backspace...

https://www.rsracing.com/tech-wheel.html#backspace

 

Thanks for the replies guys. I had seen that chart, and then used the formula to figure it out, and the two didnt agree. So assuming the chart is correct and not my math, am I dreaming using 35" x 12.50 toyo mt's or should i stick with the 33's x 12.50

 

I'd stick with 33's.

 

According to the Mickey Thompson Tires website, the formula to convert backspacing to offset is as follows:

Backspacing – (Wheel Width + 1)/2 * 25.4 = offset

Here is the formula to convert offset to backspacing:

For positive offset wheels: (Wheel Width +1)/2 + (offset * .03937)

For your 8.5" wheel with an offset of +38mm:

BS = ((8.5 + 1) / 2) + (38 * .03937)
BS = 4.75 + 1.496 (or 1.5)
BS = 6.25

Assuming the offset of 38 mm is correct, this pretty much matches with the data from the chart.

KR-Texas

PS. With that much Backspace, I think you have to stick with the 33x12.50s.

 

X2