Turbo trainers and cadence

[Lozz360]

Earlier this year I purchased a turbo trainer (Tacx Flow) and started using Zwift. One thing that puzzles me is the cadence measurement. I understand that cadence is the rpm of the crank, but how does the trainer know how fast the crank is spinning? I can see how the trainer measures speed of the bike, but the cadence will depend on what gear ratio I am in for a given speed. Am I being silly and it is just measuring rpm of the back wheel (so not cadence at all) or is there a sensor that somehow detects each time the crank revolves?

 

[BurningLegs]

Cadence can be inferred by small peaks/troughs in power output.

As you move through a full rotation of the cranks your power will vary slightly as different muscle groups are engaged. This can be detected and used to estimate cadence. In my experience it’s perfectly accurate enough.

 

[HarryTheDog]

Usually you need a cadence sensor or have a crank power meter which has the cadence sensor built in. Just google cadence sensor there are lots of different types.

 

[Lozz360]

Usually you need a cadence sensor or have a crank power meter which has the cadence sensor built in. Just google cadence sensor there are lots of different types.

Thanks for that. I don't feel I need a cadence sensor. I was just interested to know whether the rpm that was displayed on the screen was actually cadence or the rpm of the rear wheel. Probably a daft question as the difference would be substantial for say a 54/11 gear ratio!

 

[cougie uk]

Crazy idea but try counting your cadence for a minute as you turbo ? Then you'll see how accurate it is.

 

[BurningLegs]

You are right, on the Tacx flow you don’t need a cadence sensor. The turbo infers cadence accurately.

I think the newer Wahoos do it too now but for a while it was a Tacx party trick 🙂

 

[Dogtrousers]

Some time ago I did a bit of a calibration run using a separate cadence sensor and a tacx turbo. It was pretty much spot on.

 

[HLaB]

When I got my turbo (an Elite Suito FWIW) I compared a few times its power/cadence estimation compared to my power meter and cadence wise its estimation was nearly on a par with the power meter, however it is calculated. It wasn't too bad with its power estimation estimation but at higher cadence it lagged behind the power meter a bit