For some reason I am having trouble understanding...maybe it was my Canadian edumacation but I cant seem to get this..
Looking for some 15x8 IONs or similar wheels to replace my stock factory ones...and would like to have them sticking out sligtly with my 31's.
Threads about this talk about 3.75" or 4" but they dont say negative. Ive read the less BS, the more it will stick out. So is it -3.75" BS I need? Or positive??

I wont them so they dont rub on my control arms and obviously it looks better.
Sorry all, I know this has been discussed alot...I just dont get it

 

The less backspace, the more they will stand out.
So between the two you want 3.75 backspace.

 

Backspacing is the distance between the inside edge of the rim (the "backside" of the rim) and the inside surface of the rim hub. Easiest way to measure backspacing is to put a rim face down on the ground and place a level board across the rim edge. Then measure from the board to the rim hub. That distance is the backspacing. The greater the distance, the more backspacing there is and the rim will be "pulled in" due to the how far it must sit inside the wheel well to bolt to the axle hub. A rim with less backspacing "pushes" the wheel out due to the rim hub being closer to the rim edge. Make sense? If not, check out Summit's video on it:
http://www.youtube.com/watch?v=ld3WhpdCEGg

Factory XJ rims have 5.25" of backspacing. For 31x10.5x15's, a 15x8 rim with 4.5" of backspacing will easily keep the tire off the LCA's.

 

the less backspacing the more the tire will stick out. Backspacing is not affected by the width of the rim. so a 15x8 with a 3.75 backspacing will have the same amount sticking inside the fender as a 15x10 but the 15x10 will have 2inches more sticking outside the fender. I believe what you are looking at is OFFSET. offset is affected by the width. OFFSET and Backspacing basically tell you the same thing but in different ways. A NEGATIVE OFFSET will have the tire stick outside the fender, and a POSITIVE OFFSET will have the tire suck into the fender. Backspacing is the distance from the back of the wheel to the mounting surface. Offset is the distance from the center of the wheel to the mounting surface of the rim. if you want the tire to stick out a little then get a negative offset rim like -18mm. or a small number backspacing like 4 inches of backspacing