tpirman--thanks. I'm a big fan of Wheelskins too. I installed a perforated cover on mine and like you, the top half of the wheel shows more "stitch"--kind of like a ridge where the two halves meet.
Measured the wheel and the circumference of the top half is smaller than the bottom half!! Ended up going with a 15 1/4 X 4 1/8. For my case I would have been better off with a 4" overall because the perforated leather stretches a bit and the wheel is only 4" in circumference on the top half.