Detirimining RPM from MPH

Discussion in 'General Questions' started by professor, Feb 20, 2011.

  1. professor

    professor Active Member

    Never was able to pass math in school, but I think this works- if one of you math gurus find an error- tell me.

    You only need to know the speed and gear ratio for the bike-

    Tire rolling legnth for one rev (mark the ground with you on the bike as you roll it). In my case a 24 inch wheel the distance is exactly 6 ft.
    One mile (5280) divided by one tire rev (6) = 880 X speed (in my case peak power flattened out at 25 MPH in second gear).

    880 X 25 mph= 22,000 wheel revs per hour divided by 60 gives 366 revs of the wheel per minute.

    366 X gear ratio 14.2 = 5206 RPM.
    This seems right for my HF79, which is a pushrod 4 stroke.

    Now if the bike was in 3rd gear, it would not pull max RPM.
    This test was to see how fast this motor spins over at peak power.

    Do I have the math right?

  2. srdavo

    srdavo Active Member

  3. ibdennyak

    ibdennyak Guest

    Do I have the math right?[/QUOTE]