So I got one of these things for my birthday and tried to install it today. So smittybilt's site said that you mount the base on your tire rack, then slide the wheel back on and bolt it down with the factory lugs. This leaves a square tube (looks kinda like a hitch receiver) sticking through the wheel that the rack bolts to. However the stock wheels, (even with the center cap popped out) will not slide over it.
Anyways, it fits without the spare wheel. And the cart i wanted to mount on it mounts good. But I have to carry the spare inside the jeep when it's installed.
One handy thing though, the base mount is patterned to fit both JK and TJ bolt patterns. Flip it one way for TJ, flip it 180 for JK.
Maybe I will just have to go get a spare wheel with a bigger center hole. Any ideas for a cheap but reliable 15" stock size replacement wheel that has a larger center hole.