Originally Posted by
caloso
48x12 = 105 g.i. = 28mph @ 90rpm
for anyone wanting to see the math behind that calculation.
it confused me until i learnt that gi is the diameter of the imaginary "wheel" not the circumference.
so let's see:
105gi x 3.14 x 90rpm = 29700 inches/minute.
29700 inches/minute x 60 (minutes) = 1782000 inches/hour.
1782000 inches an hour divided by 63360 (inches in a mile) = 28.125 miles an hour
there we have it, bang on target.
it's interesting that the 48x12 gearing means you're somehow driving an imaginary wheel 105 inches in diameter. that's a big wheel.