It would sure be nice to derive virtual cadence from speed for fixed gear bicycles. Given a speed and gear ratio, a cadence sensor is redundant since there is only one gear and no freewheeling. Even better would be a way to add the virtual cadence data entries to the recorded data file.
shouldn't be too hard to create such app (data field).
As a fixie rider, I always place a cadence sensor - for me, it is more important than speed.
I created an data-field app (never put it for the public, but I can...) that calculating the gear inches. it is interesting to see that speed is not very accurate (assuming that cadence is just a counter from the sensor while speed is linear calculation of the GPS and time).
the app show all 3: cadence, speed and gear inches. when on a gear bike it nice to see when I change gears what is the inches; on the fixie it a bit annoying to learn that the the numbers change +/- an inch or two.
so I want to believe that using the not-perfect speed number to calculate cadence will be not very accurate.
as far as placing it into the FIT file - I don't know about that...
It seems you'd need to take the distance traveled in the last second (or few seconds) divided by the circumference of the drive wheel, then you'd multiply that by the inverse gear ratio. Once you have it calculating a correct value, you could write the result to the .FIT file pretty easily. Everything you need to know about that part is captured in the Moxy sample program.
Looks like SHPRUNG never updated it for newer devices. If they don't reply here, you can try clicking Contact Developer on the store page to reach them.
If you still have your old Edge 520 (or you know someone who owns one of the app's supported devices), you can try sideloading the app from the other device to your new Edge 530.
These instructions were intended for watches, so I'm not 100% sure if they'll work on an Edge.
I think you can also use the AppBuilder 5 | Garmin Connect IQ for this purpose - it is quite flexible and allows you to create the needed output easily.
