Cadence is wrong on large cassette chainring

Hi Zwifters,

I get lower rpm readings on large cassette chainrings.
My current setup is 50/34 with 11-36 mounted on a Wahoo Kickr Core and using a wireless crank mounted Wahoo cadence sensor. Everything works fine on all gears except the 34-36 combination where I get the rpms show half the value of all the other speeds. I had a 11-32 cassette before and everything was fine. The second gear going down on the 11-36 is a 32 and it works fine.
Considering that you don’t have to enter the details of the bike setup on Zwift or Wahoo material I don’t understand what’s going on.
Any ideas?

I think this is more of a limitation of estimating cadence in the way the core does. From memory it looks at small regular fluctuations in your power (or at least that’s how I assume it works, similar to a pedal analysis). When you are in a really low gear maybe you are spinning really smooth and the core is actually picking up every second pedal stroke or something like a left leg dominance?

I saw the same thing on the flat when I tried my mtb on my core. I think it went away when I had to push harder.

I’ll try pushing harder next time I ride it

Although I easily reached in excess of 270 on 14% grades.

I also got this cassette in hopes of Everesting. Pushing hard on it was not the plan.

I may have to live with this. :frowning:

That sensor should be oblivious to your cassette. It should just measure how fast the crank arm goes around. Are you sure that’s where Zwift is getting your cadence?

I completely missed that bit of information.

The wahoo Kickr core does not have a cadence sensor. I had to buy a separate.
It works fine with every gear except the 36.
It simply doesn’t make sense.
Well at least I can’t figure it out.
Maybe my pedal stroke is not smooth enough.
I’m used to grinding up hills.
I’m going to pay more attention to my stroke the next time I do Alp the Zwift.
Thanks for the comments :slight_smile:

The kickr core has cadence after a firmware update. If you are connecting an external cadence sensor then your smoothness will not be important.

Thanks for the heads up :slight_smile: Ben
I did apply the firmware to the kickr core but had not looked up what it added to the functions.
Guess I should had realised that I no longer needed to spin the crank to activate the cadence sensor.
Zwift pairs itself with the Kickr core cadence by default.
I’ll be bypassing this from now on cause I got no issues with the crank sensor with any of the speeds. It also made me realise that the bad tracking of the kickr core cadence sensor made the power tracking unreliable. It created erratic power readings. Specially on the cassettes 36 tooth gear.
Everything runs super smooth now.

I’ve experienced the same issue on 2 smart trainers. The first was a Tacx Vortex using its built cadence. The lowest gear (34x34 spinning around 90/95 rpm) and sometimes the second lowest would always show 1/2 my true cadence. I lived with it. Fall ‘19 I purchased a Kickr Core after their built in cadence update was released. Same issue. So…I purchased a Wahoo cadence sensor and mount it to my left shoe and no more issues.

Would this have any impact on power?

No it doesn’t. It’s just annoying