A Gearing Calculator for multi-sprocketed directly-driven small wheels

(See here for a hub-gear calculator).

How to use:
Define wheel size by (A) choosing ERTRO/ISO rim diameter and (B) tyre width. The nominal widths are 25, 28, 32, 35, 37, 40 etc, but you can input whatever value you like. The calculator formula (A+2B)*25.4*C/D1, D2, Dn 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 variable (C) is the chainwheel size.

Finally pick a nice set of freewheel sprocket sizes (D).

The result for each "speed" (yellow fields) is presented in the established "gear-inch" format. Best viewed with IE font size set to "smallest".

A) Rim size:

346- [mm]

357- [mm]

369- [mm]

406- [mm]

B) Nominal tyre-width:
C) Chainwheel:
D) Cog #1
[t] ["]
  Cog #2
[t] ["]
  Cog #3
[t] ["]
  Cog #4
[t] ["]
  Cog #5
[t] ["]
  Cog #6
[t] ["]
  Cog #7
[t] ["]
  Cog #8
[t] ["]
  Cog #9
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      Gear inches: