OK then I have both wheels side by side on the garage floor. As far as I can tell the only difference is that the XR600 wheel has a metal colar on the sprocket side that the spacer seems to be pressed into and the disc is a different size. The axel on the 650 is bigger as of course are the seals the bearings and the tube which is inbetween the bearings. Everything else looks and measures the same. So my question is this. Can the bearings and the seals and the tube between the bearings be swapped? It looks like they can be. I wil be looking into it further but if anyone has done the swap please let me know the results! I have not tried the front wheel yet but I am betting that the axel size is the same for both wheels. It would make since that Honda would use the same hub if possible and just increase the axel size and thus the bearing size on the rear wheel to make up for the difference in horsepower. The front size really would not need to change.