backspacing doesn't add up? help me understand!

Hey all! I have some 17x9 renegade raceline wheels that came on the truck when I bought it. They are listed at 0 offset and 5 backspacing. I'm doing all the lift, tire research as I'm in need of some new tires sooner than later and want to buy once cry once. I'm concerned about the 5 backspacing working out with anything larger than a 265/70r17, but whatever the real reason I'm here.....

Wouldn't 0 offset put the backspacing right at 4.5? As in it's right in the middle of the wheel (no offset) and the wheel is 9 inches wide (9/2=4.5) Will somebody point out the error in my ways?

 

You need to add an 1” to rim width
Herw is a chart

 

You can fit up to a 12.5" wide on that wheel, no worries

 

Why do you have to add an inch? Where does that come from? I get it, but just wondering why?

 

Less worried about width of tire and if it will fit on the rim, but more if it
s backspacing will put the tire into the UCA or anything at full droop.

 

I don't believe it's a whole inch. I've always used 1/2" as my adjustment. Backspace is from the back lip to the mounting surface, not from the inside lip of the tire bead seat surface so I assume that is where the measurement adjustment would add in there

 

I'm telling you from experience I've ran 35x12.50s on that wheel spec on half a dozen of my Toyotas over the years and IMO it's about the ideal backspacing for these trucks. However a 9" wide wheel on a 265/70/17 is likely out of spec for that tire. I think most approve down to 8.5" wide, the 9 is a touch wide for that size tire. That said, I ran that size on that wheel and never had an issue at all. Just some tire shops may say they won't mount because tire MFG doesn't recommend it.

 

Backspace is expressed in inches. Calculate backspace as follows:

Wheel width ÷ 2 + offset + ½” = Backspacing