Well, if it's a 21 inch radius then the circumference is 132 inches = 3.35 metres.
2 * 3.14159 * 21 = 132 in 132 in * 2.54cm = 335 cm = 3.35 m
100 km/h / 60 / 60 = 27.78 m/s (metres per second)
27.78 / 3.35 = 8.29 revolutions / sec [8.3 Hz]
Well, if it's a 21 inch radius then the circumference is 132 inches = 3.35 metres.
2 * 3.14159 * 21 = 132 in 132 in * 2.54cm = 335 cm = 3.35 m
100 km/h / 60 / 60 = 27.78 m/s (metres per second)
27.78 / 3.35 = 8.29 revolutions / sec [8.3 Hz]