Inaccurate cadence?

Equipment
1

I have the newest Kickr. I have my road bike attached. I just recently started using TrainerRoad (A few weeks now) and have noticed the cadence sporadically jumping significantly (e.g., 85 to 115) when as far as I can tell my cadence isn’t changing at all. The correction takes a variable amount of time, sometimes as long as 45 seconds or so. Does anybody have any ideas what could be contributing to this?

It’s having me questioning the power/FTP too, only because I have no baseline to compare it to.

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2

Smart trainer cadence isn’t very accurate. Best to use an external crank based sensor.

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3

I had no idea, thanks for the response. I’ll look into a crank based sensor.

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4

According to @dcrainmaker and @gplama most modern trainers can infer cadence very accurately.

The behavior you see seems odd, at least when compared to Ray’s review of the 2020 Kickr (which is largely identical with the 2022 model you have):

5

Yep, can. It’s highly dependent on the pedalling style.

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6

Have the new Kickr. The only cadence issue I have is in ERG mode once I get over 110rpm it drops back to about 1/2 of what I’m doing. No issue if I use the Di2 cadence instead of the Kickr.

7

I think when I used the Suito 's calculated cadence it was the one thing thatcwas fairly accurate but I mainly use a power meter which records cadence.

8

My Saris H3 is garbage for cadence and always has been. It’s funny because it’s been a known issue since release and they seem unable to do anything about it. Certainly one for use with a power meter or other cadence source.

9

Bear in mind that if cadence is wrong, then power in erg mode is wrong. I’d contact the manufacturer and have them troubleshoot. I’d demand a new trainer if they can’t fix it with a firmware update. That makes the whole ‘smart’ element of the trainer useless

10

I too have an H3. It’s cadence measurement is never going to be as good as a crank based sensor — even if it’s correct, it will lag.

I use a Garmin cadence sensor and that works well.

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11

That’s not true. Smart trainer power calculations are based on the internal pulley and belt system for the RPM values used. It is a fixed and known set of values with the RPM related to the internal drive ratio.

There is absolutely no issue with power data even if the estimated rider cadence is incorrect.

The smart trainers can only estimate rider cadence by looking for power “pulses” that we create as humans. Those high and low surges from the dead spot in our pedal stroke are how they estimate the rider cadence. It can be good or bad cadence data depending on the smoother or rougher rider cadence.

Again, even of rider cadence is erratic or incorrect, that does not mean power data is flawed.

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12

So you’re saying the rpm of the fly wheel?
I thought erg used cadence to determine whether it should increase or decrease resistance. I guess it would be that it is measuring the rpm on the fly wheel, which is controlled by cadence?

13

I have a Saris H3…its horrible for cadence…usually reads in the 50’s when I am 90+. Get a crank based sensor.

14

No. Most trainers measure changes in flywheel speed and resistance setting to infer power. However, flywheel rpm ≠ cadence, the latter is the rpm of the crank.

I am certain that trainers use periodic fluctuations in power to determine cadence. On each revolution of the crank you have two “power strokes” (left and right, respectively), and this periodicity is something you can detect relatively easily in a signal.

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