Karamba and K-Diag speedo pulse frequencies are erroneous

[frankenduck]

If you want links to bad software, here it is for free:

https://www.kbikeparts.com/classickbikes.com/ckb.tech/0.ckb.tech.files/speedocal/Karamba.exe

https://www.kbikeparts.com/classickbikes.com/ckb.tech/0.ckb.tech.files/speedocal/K_DIAG.zip


Let’s start with speedometer pulse math. It’s very straightforward:

All K final drives emit 6 pulses per rear wheel rotation.

For this example I’ll use a K1/K100RS4V/K1100RS rear tire – 160/60/18.

It has a circumference of 2040 mm so it turns 1,000,000/2,040=490.2 times per kilometer.

At 100 kph it rotates 49,020 times per hour. It generates 49,020*6=294,112 pulses in one hour. That’s 294,112/3,600=81.7 pulses per second or 81.7 Hz.

Both Karamba and K_Diag only emit 80Hz at the 100 kph setting which means that if you calibrate right on with either software you speedometer will still be running a little over 2% faster than your actual speed.

Also of note is that every single bike model puts out 80 Hz at the 100 kph setting so despite the change in tire circumference the software does not take that into account.

And it gets worse. If you enter 160/16-18 as an alternate tire size for any other model (K75S for example) then the K Diag software emits a 78 Hz signal at 100 kph which is even more erroneous – about 4.5%!

BUT there is hope!

Here’s my calculated table of correct frequencies for various rear tire sizes at various speeds:
JPG: https://www.kbikeparts.com/classickbikes.com/ckb.tech/0.ckb.tech.files/speedocal/K.Bike.Speedo.Cal.jpg
PDF: https://www.kbikeparts.com/classickbikes.com/ckb.tech/0.ckb.tech.files/speedocal/K.Bike.Speedo.Cal.pdf

You can use those values with a program like this freeware app to generate more accurate frequencies for speedometer calibration:
https://www.kbikeparts.com/classickbikes.com/ckb.tech/0.ckb.tech.files/speedocal/tone.exe

(You can type whatever you want into the initial popup.)