Crackle said:
Elaborate on the first please becasue I'm not sure I catch your drift but you might be on to something.
Apologies for misspelling
diameter earlier!
I know it isn't relevant now since you've confirmed that the wheel diameter was the problem, but out of interest - what I was getting at is that computer software can work with either
Real numbers or
Integers. Real numbers include the information after the decimal point so Pi would be 3.14159265.... Integers are just whole numbers 3, -17, whatever. An Integer approximation to Pi might be 3, which is obviously significantly different to the actual value. A well-known better approximation is to multiply by 22 then divide by 7, but you still wouldn't get an accurate result. It might be easier to give you examples:
C(ircumference of wheel) = 2 * Pi * R(adius of wheel) = Pi * D(iameter of wheel). Taking your 700/32 wheel... D = 27 inches.
Real calculation: C = Pi * D = 3.14159265 * 27.0 = 84.82300165...
Integer calculation with Pi ~= 3: C = Pi * D = 3 * 27 = 81
Integer calculation with Pi ~= (22 divided by 7). Interestingly, you get two different results depending on the order of the calculation!
(a) C = Pi * D = (22 * 27) divided by 7 = 594 divided by 7 = 84 (the decimal part of the answer, .85714286..., being lost). This is obviously a better result than just approximating Pi to 3.
(B) C = Pi * D = (22 divided by 7) * 27 = 3 (the .142857143... part being lost) * 27 = 81 again. Doing the Integer calculation this way round is equivalent to using 3 as the approximation for Pi.
When computer hardware was less sophisticated than it is now, Integer calculations were much quicker than Real number calculations which needed extra (slow!) software to do the maths. Modern computer processors have very powerful dedicated number-crunching hardware built in to do Real number calculations so there is less reason to resort to Integer maths.
I don't use spreadsheets, but I was assuming that there might be the possibility of specifying whether the calculations were done with real numbers or integers. Maybe they are always real? I don't know***...
PS ***I just checked Microsoft Excel - apparently it always calculates using real numbers (a.k.a. floating point numbers).