greenjeans -
Measure the bead width of your rim. I have one which is 1 7/8" and one which is 2 1/4".
I don't have a tire/wheel chart handy, so I don't know if these are WM1 and WM2 or what...but the smaller one is a CB550, and the bigger is a CB750...both should work; the bigger will take a fatter tire...