Tacx Flux S - power for specific cadence changing start to end

Hi all, first time poster.

Recently upgraded my old dumb trainer to a Tacx Flux S mid range smart trainer. Have noticed that when I start at the beginning of a session that the power output at x cadence reduces between the start and end of the run, e.g.

Start - 85rpm - 140w
End - 85rpm - 115w

(In erg mode)

Figures aren’t exact but hope they illustrate the point, it is as significant as 20w+ though which seems odd…

Any insight to this would be great?

Is the software on the Flux up to date?

Do you calibrate the Flux every ride? After the warm up part of a workout, usually at nine minutes, I calibrate my S and then complete the workout .

No issues with power fluctuations here.

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This means you are sitting on the power floor, and TR is demanding less power than what you are delivering. The Flux S has a pretty high minimum power vs “wheel” speed line, which means you often need to shift to a sorter gear during the recovery parts of a workout. The minimum power deliverable does go down as the trainer warms up - that’s what you are seeing. You also see the same behavior if you go in resistance mode - the power required at a given gearing, cadence and resistance level goes down over 20-30 minutes as the trainer warms up. If you are in Erg mode and not sitting on the resistance floor, this should not impact you in any way.

If you make your TR data public, I can confirm the above.


Firmware all up-to-date thanks. I often calibrate after the warmup too, but sometimes creates a bit of a hoo-ha with the device dropping off of my tablet so i’m not religious with it.

Thanks for the tips though, appreciate it.

This sounds like it might be my issue. Im in the 34 chainring and somewhere in the middle in the back (if I recall correctly it asks you to set it up like this), and I know at the rest intervals i’m at the power floor as it often hovers above the target power - hence why i’ve only noticed this phenomenon at the start/end & rest intervals.

The drop in resistance as the machine warms up makes sense, I’m sure you’ve nailed it. My training intervals are all 200w + so assuming erg mode should be delivering these fine if I’m not near the floor as you say.

Data is public - I’ve added “end1”, “end2” & “end3” intervals to Ebbetts from Thursday which illustrates what i’m talking about, and it ties in with what you say.

Many thanks

Confirmed - that behavior during the recovery segments is typical. You are above the TR power demand. If you’re not on your shortest (easiest) gear, shift to it for the recoveries, and back up for the interval sets, unless the power level does not bother you.

Recognize this behavior? That was me last year, before I upgraded my old clunker that sits on the trainer from a 7-sp to a 10-sp machine. My lowest gear was way too high. You can see the recoveries going down in power as the workout progresses and the trainer warms up.

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