Hello everyone,
I’m using a Tacx Neo Bike Plus which is connected via bluetooth to my Windows PC about 1,5m apart.
Yesteray I was racing a ladder race when I noticed something strange. Since my team was up in front by quite a bit, we had the luxury to take it easy on some parts of the course. So I stopped pedalling now and then - while my power dropped to 0, sometimes the cadence of my virtual rider spiked instead going up to 200 rpm. This resulted in a DQ for me (kind of understandably, although high cadence with zero power won’t give me any benefit) and I really want to avoid that in the future.
I already uploaded the log file to Zwiftalizer, but besides some bluetooth resends (which don’t overlap with the issues) there are no issues:
On Intervals.icu it looks like this:
Any idea what could cause this issue and how to resolve it?
The cadence sensor is built into the crank so I imagine what you are doing it stopping then pedalling backwards a bit get into the right position to start again. The sensor will then have 2 hits very close together and spike the number. Just jump on the bike offline and try to trigger it via the onboard display to see if thats the issue.
Hi Steve! Thanks a lot for your input - I will try it tomorrow morning, so that I don’t disturb my neighbours now. 
One thing though: Based on the Tacx site the cadence on my Smart Bike isn’t measured by some sensor, but internally:
Tacx interactive trainers measure your cadence without the help of a sensor. The trainer is constantly aware of your speed and uses it to define your cycling movement. The speed is zero at the top of the pedal stroke and it reaches its maximum in between. With this information, your trainer knows when you have made a full circle and uses this to define your cadence.
But, just to be safe, I’ll try your suggestion anyhow tomorrow morning. 
It’s an internal magnetic cadence sensor.
Ah, that’s good to know - thank you. And you are absolutely right - I was able to reproduce it right away.
Now I “just” have to refrain from doing that during the race.
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You could also try putting a cadence sensor on the crank arm. Even the cheap ones should have an accelerometer instead of a magnet
https://support.wahoofitness.com/hc/en-us/articles/204280044-How-do-the-RPM-Speed-and-Cadence-sensors-work
Thank you for the idea, Paul. I’ll see, if the problem persists and if so, I’ll look into buying an additional sensor.
