But also, if it's a smaller diameter than the stock rear tire, you don't want to run it on the rear for very long since the left and right sides will turn at different speeds and it could burn out the clutches in the LSD.
I bought a rim and tire from discount tire, a long while ago. They said it would fit, I said no problem. 4 months down the road I had a flat and it did not clear the calipers. Discount said sorry bout your bad luck. I'm gonna assume they used cts spec. And I'm might assume a cts doughnut won't fit