help on backspacing

hey guys and gals
im running 35s on 18x10 and they rub a little on the body mount and was wondering. what backspacing i need to fix this problem? i have no clue on what the backspacing is now. the tire shop told me to go with a 8" or 9" width. but they couldnt tell me on what backspacing to use.

thanks

 

Im guessing you have too much positive offset. What is your offset?

 

lots of people running those smaller widths with no issues

 

how do you measure to find out what the backspacing is?

 

flip over the tire and lay it flat on ground upside down. lay a board or
ruler across the rim and measure the distance b/w the bottom side of
board and where the tire mounts to the truck. that is your backspacing.

 

5" Backspacing and -12MM offset