Originally Posted by
woodcraft
A very large rider will push the tires down, in effect making a smaller wheel diameter, throwing off the speed calculation.
Actually the calculation is not based on diameter, It is based on circumference. Which does not change with weight when properly inflated.
If the correct formula is used (grade 9 math at best) these calculators are probably 99.9% accurate.
I get almost identical results as the online calculators when I set up an Excel chart for the same gear ratio to speed calculations. The tiny differences are probably due to rounding.