Originally Posted by
Happy Feet
...
FWIW, this is the maths I came up with
One revolution is 2100mm = 210cm's.
1km = 100000cm's.
100000/210 = 476 revolutions.
27.5mm = 2.7cm's deviation per revolution.
476 revolutions x 2.75cm's = 1285cm's
1285cm's = 12.85m
So... if my thinking is correct, I would have a discrepancy of 12.85 metres for every 1 km travelled.
or.. 12.85 meters x 100km's = 1.285 km's per 100 km's traveled.
If that is correct, would it also stand to reason that if I were travelling at 25km's per hour I would have a speed discrepancy of .32 km's per hour?
1.285 meters per 100km's / 4 = .32.
My math was simpler, I divided 2155 by 2100 and subtracted 1:
2155 / 2100 - 1 = 0.026 or 2.6%
and then if you pick the mid point and allocate half that 2.6 percent error to each option, that is 1.3 percent error for each wheel choice. So, use 2127 or 2128 for your computer setting, mid point between 2100 and 2155.
Or you could use logarithms, ....