- The circumference of the pedal sprocket is twice the circumference of the wheel sprocket, because its radius is twice as big.
- As the pedal sprocket turns through 1 complete revolution, the chain moves through a distance equal to the circumference of the pedal sprocket.
Therefore the chain must make the wheel sprocket turn through 2 complete revolutions for every 1 revolution of the pedal sprocket. So:
(a) The angular speed of the wheel sprocket is rpm.
(b) The wheel is also turning at 80 rpm. So in one minute, the bicycle moves a distance equal to 80 times the circumference of the wheel inches.
Can you work it out from here?
(I make the answer 9.08 ft per sec, or 6.19 mph.)