Converting a Basic Bike computer to count Cadence

[Guest Big H]

I tried this long ago, it worked but kept me doing arithmetic on the bike. Arithmetic is difficult if your sugar levels dip. It is much easier and cheaper in the end to buy a speedo already equipped to measure cadence.

[MarkD]

You should be able to get this to work provided you only ever ride in 1 gear on the trainer..... 

From the equation:

Cadence x Gear Ratio x Wheel Diameter = Speed

C x GR x D = S

Where: Gear Ratio = Teeth in Front  / Teeth in rear  [GR = F/R]

 

To get the Speed in km/h multiply cadence by 60 (cadence is revolutions per minute) and divide Wheel diameter by 1,000,000 (convering the mm to km)

 

60xC x F/R x D/1,000,000 = S  (in kph)

 

At this point, decide what Gear you will ride in - for example, 53 / 15, and measure your wheel diameter (road will be approx 2070mm)

 

So:

60xC x 53/15 x 2070/1,000,000 = S

 

ie. 0.43884 x C = S

 

or solving for S = 2.278735 x C

 

Now, with your current wheel Diameter setting your speed is 2.2787 times your cadence - eg if your speed reads 40, your cadence would be 91.

 

To ensure your speed is the same as your cadence, multiply the wheel diameter by 2.278735 ie. 2070 x 2.278735 = 4717 mm

 

Problem solved - your speed reading will now be your cadence.

 

Note 1 - Substitute your own acual values

Note 2 - This only works if you are only going to ride in ONE gear

 

 

[fandacious]

or put your magnet on your crank and enter your crank length into wheel size field...

 

much simpler

[MarkD]

or put your magnet on your crank and enter your crank length into wheel size field...

 

much simpler

 

Still going to need to do some maths as this will simply give you the velocity of the tip of your crank - you still need to "fudge" the numbers to convert back to revolutions per minute.

 

This method however does have the advantage of eliminating the gear ratios as a "variable" so will work regardless of the gear you are riding...

 

And the simplest method is to spend the money and buy a computer with a cadence function!!!!!

[Gert Janse v Rensburg]

or put your magnet on your crank and enter your crank length into wheel size field...

 

much simpler

 

Multiply it by 10 and you wont have the calculation of 9,7km/h=97cadance. But actually get 97km/h whitch I think takes out all the calculations in your head....