How to use:
Define wheel size by choosing ERTRO/ISO rim diameter (A) and tyre width (B). The nominal widths are 25, 28, 32, 35, 37 and 40, etc, but you can input whatever value you like. The calculator assumes that tyre-width equals the tyre's actual "height", i.e. half the difference between the outer tyre diameter and the rim seat diameter.
The next variables are the chainwheel size (C), and sprocket size (D).
Finally, select the ratios that correspond to the gear-hub model to be analyzed (E). (See here for a table of gear-hub data).The computation formula used is (A+2B)*25.4*C/D*E/100. The result (yellow fields) is presented in the established "gear-inch" format. Best viewed with the IE font size set to "smallest".