I'm trying to figure out the optimal wheel backspacing. Currently I have 17" X 7.5" stock rims with a 6.25 BS. I have 34" x 11.5" tires and a 2.5BB with absolutely no rubbing whatsoever.

Now if I wanted to change my rims to 8" wide but use the same tires and want them to be in the same position then my backspace should be 6.5" right?

So now if I wanted to get a tire that is 1" wider but have the inner sidewall the *same* distance away from the wheel well as the last tire then the backspace should be 6.0" right?

Now I want to get 35" x 12.5"(which is 1" taller and 1" wider). Because the tire is taller I play it safe and get a BS with 5.5".

So is a BS of 5.5" enough with a rim width of 8" for 35 x 12.5 tires? I don't want my tires to stick out farther than I have to.

 

Now if I wanted to change my rims to 8" wide but use the same tires and want them to be in the same position then my backspace should be 6.5" right?
Correct!

if I wanted to get a tire that is 1" wider but have the inner sidewall the *same* distance away from the wheel well as the last tire then the backspace should be 6.0" right?
if you have a 6.25 BS and like that distance, your new tire at 1" wider will be in .5" farther. You will need to get 5.75" BS. Or, subtract .5" of BS from whatever you had before.

So, with that said, in theory you are correct. You should be fine with 5.5", it will add an additional .25" of back space to the factory settings. Althught, do note, that your tires will stick out about .75" father because of width and back spacing.

 

Most companies seem to agree that a 4.5 inch backspacing is ideal if you want 35x 12.50. Alot of people are getting away with using Spydertrax spacers with the stock wheels though.

 

Ya thats what I hear from this site too but it sounds like a full inch too much.