The gear ratio $R$ is inversely proportional to ratio of the number of teeth, $N_a$ and $N_b$, of the two gears. $$R=\frac{N_b}{N_a} $$ The beltmodules uses the same concept as shown in the picture below, from dynamicscience.com.au where the gear train of four gears are connected, and the gears “B” and “C” are fixed together on the same shaft. From this it is possible to derive the gear ratio formula $$R=\frac{N_b}{N_a}*\frac{N_d}{N_c} $$

The beltmodule has the following gears

• $ N_a=22 $
• $ N_b=80 $
• $ N_c=10 $
• $ N_d=20 $

which gives the following ratio $$R=\frac{N_b}{N_a}*\frac{N_d}{N_c}= \frac{80}{22}*\frac{20}{10}= \frac{160}{22}=7,27 $$