In the following way we have calculated the gear ratio we need to achieve the desired speed.

Gear ratio

Circumference band
1inch = 2.54 cm
14 inches = 35.56 cm = 0.3556 m
Pie x diameter = circumference
Pi x 0.3556=1.117 m

Desired speed = 45 km/h
45 km/h = 45000 m/h
45000 m/h : 60 = 750 m/min

The required speed to calculate the ratio
750 : 1,117= 671.44 RPM
4250 RPM : 671.44 RPM = 6.33
So the ratio is 1 to 6.33

Our sprocket is 12 so 12×6,33=75,96 teeth

If you round off the ratio 1:6
12×6=72 teeth

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