I'm looking to find the back spacing for a 17x9 +35 rim. Does backspacing go hand and hand with offset? I came out with the number 6.2in, is that right? I wanted to get some custom diamond racing wheels.

 

 

Youre very close. its actually 6.38.

A "9 inch" rim barrel is actually 10" overall since width is measure on the inside edge of the lip. So 10in = 254mm. 254/2 = 127mm. so the centerline is 127mm from the outside edge of the barrel. Add your +35mm offset you get 162mm or 6.38in backspace