In reply to Keith Tanner :
Easy math.
If you keep the same offset and go from 9.5" to 10", you will have 0.25" more backspace and 0.25" more poke. That's because offset is defined by the centerline of the wheel. I'm assuming the width of the actual lip around the edge of the barrel is a constant here.
I like this, it's the simple to help me go from what I have to what may work.
My wheel width dimension was assumed accurate to the inside of the lips but you are correct offset to backspace is a fuzzy number due to lip thickness, and I didn't add any lip thickness at all. And that is how this whole wheel fitment can get confusing.
Fortunately for me plenty of cars like mine hit the track and know what fits.
