# Calculate MPH on the tire based on RPM of the hub?

I’m building a pitching machine that has an 8” wheel (16” OD tire) that is directly mounted to a 1/2” motor shaft.

Most similar questions reference a gearbox or pulpy system, but my situation is directly mounted to a 12v motor shaft.

Due to motor/fabrication design, the closest I can get my magnetic rpm sensor is a radius of 5” from the shaft.

So known variables for the calculation will be RPM at a diameter of 10” and the OD of the tire at 16” all on the same wheel.

How do I calculate the speed (MPH) of the tire?

I would imagine the OD of the tire runs slower than the shaft.

I hope this makes sense.

$$v= 16/12 *\pi*100= 133*\pi (ft/m)$$
• Not sure if this is correct. The wheel makes 100 revolutions in 60 seconds (RPM!) and each revolution travels 16/12 x $\pi$ feet. $v = 16/12 [ft] \times \pi \times 100 / 60 [s] \approx 7 ft/s$ 1ft/s is 0.681818 mph – D Duck Mar 10 '20 at 23:57