Offset & backspace Q

[DK832]

I've seen https://www.rsracing.com/tech-wheel.html linked a couple of times and was just looking at the offset vs. backspace table they list while trying to figure out the FR500 wheels I need.

It's friday, the week was long, we were out drinking last night, BUT is the table offset 12mm or am I being stupid?
If the formula is:

Offset = Backspace - (Rim Width ÷ 2)

Wouldn't a 8" wide rim have 0 offset at 4" backspace... And not at 4.5"???

 

[CraigMBA]

Depends on where the mfg stops measuring to.

Some count the lip (an 8" wide wheel is actually 9" wide from lip to lip, making a 0 offset wheel 4 1/2 backspacing).

Others don't (making the same 8" wide wheel 4" backspacing, still 0 offset).

Good luck.

 

[DK832]

Aha, thanks. Also just found this that explains it.
http://www.vintagewheelworks.com/tech-offset.php
I just wasn't aware the the "advertized" rim wheel width is inside the lips...