Cadence Calculator

 
Starter for 10 from my own spreadsheet is a formula I devised, there might well be a better way.

Speed = Gear inches*cadence in rpm*(pye*60)/63360
Gear inches = wheel diameter*(front chainwheel teeth/rear chainwheel teeth)

Put the two together in a spreadsheet and you should have it all.

Now my gear inch calculation is slightly out sometimes, so if someone knows why I'd appreciate a heads up, though it's generally close enough for my purposes.
 

ColinJ

Puzzle game developer
Sheldon Brown's Gear Calculator is handy for that kind of thing, although it gives speeds for different cadences, rather than cadences for different speeds. It is easy to look up the figures in the generated tables. Cadences of 40, 60, 80, 90, 100, and 120 rpm are supported directly. It is easy to work out figures for 30 rpm (60 rpm speed / 2), 33.33 rpm (100 rpm speed / 3), 45 rpm (90 rpm speed / 2), 50 rpm (100 rpm speed / 2) and so on...
 

ColinJ

Puzzle game developer
Crackle said:
Gear inches = wheel diameter*(front chainwheel teeth/rear chainwheel teeth)

...

Now my gear inch calculation is slightly out sometimes, so if someone knows why I'd appreciate a heads up, though it's generally close enough for my purposes.
It's not doing Integer division is it? I.e. WD*(53/13) should give you WD*4.0769... not WD*4.

Another possibility is that you are not caclulating the wheel diamater properly for the size of tyre you are using?

How do you know that the calculation is out sometimes?
 
ColinJ said:
It's not doing Integer division is it? I.e. WD*(53/13) should give you WD*4.0769... not WD*4.

Another possibility is that you are not caclulating the wheel diamater properly for the size of tyre you are using?

How do you know that the calculation is out sometimes?
Elaborate on the first please becasue I'm not sure I catch your drift but you might be on to something. I think the wheel diameter is right, trying to find an accurate table was the hardest part.

I know it's out because comparing it to Sheldons calculator can show a 2 or 3 inch diff in certain combos but he doesn't show his calculations just the results.
 
Ah! Scrap that. I musta fixed it at some point. It's spot on, you just have to make sure you get the wheel diameter right;so:-

700x23 = 26.28
700x32 = 27
26x1.5 = 24.87
 
What you end up with on the spreadsheet is something like

12 13..................25
49 107 99 51.5
90 28.73 26.52 13.79
42
80

You just change the bold numbers to suit gearing/cadence (cadence is blue)

In fact PM me your e-mail, I'll send you the flippin spreadsheet, that's easiest.

Edit: the numbers won't stay in line.
 

Keith Oates

Janner
Location
Penarth, Wales
You could ride at certain speeds and then count the pedal strokes in a minute. Not as convenient as a calculator but it gives you a good idea of your normal cadence when out riding!!!!!
 

ColinJ

Puzzle game developer
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).
 
Ah I see. No as you say it uses real numbers by default. I thought at first you were referring to it possibly working in hundreds instead of 60's.
 

BentMikey

Rider of Seolferwulf
Location
South London
58.6km/hour and 185rpm on the fixed this morning!!! Wooohooo! I'm even more impressed that I still had the composure to look down at the cycle computer whilst doing that.
 
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