Resistance Smoothing


(Russell Gowers [CRANKS] KISS (C)) #1

I’ve seen a few posts on this but I wanted to bump it.

I use an ANT+ power meter (Quarq Elsa R) and a Tacx Flow T2240 controllable trainer.

When I use the trainer in ERG mode for a workout, the resistance increases correctly to allow me to hit my targets at 90-200% FTP. However, as soon as I get to the “rest” segments at <75% FTP, it feels like the trainer does not decrease resistance quickly enough. For 5-10 seconds after the end of the effort, the trainer remains on high resistance, then drops dramatically.

This can lead to some yo-yoing with the following pattern

  1. Resistance is too hard

  2. I put out too many watts

  3. Trainer drops resistance dramatically

  4. I increase cadence because of easy resistance

  5. Trainer increases resistance again

  6. I put out too many watts

  7. goto 2)

It takes a good 20-30 seconds for my “rest” interval to completely stabilise. Basically it feels like the feedback loop between the power meter, the laptop and the trainer is very laggy.

Could this be an issue specific to my trainer or my power meter, or is this a known bug across the board?


(Ken MacPhail) #2

I have a Tacx Vortex Smart trainer and I noticed the same fluctuations you are having. I went out and bought a separate cadence monitor and set Zwift to recognize the new cadence monitor. Solved my fluctuation issues.


(Russell Gowers [CRANKS] KISS (C)) #3

Ahh - intriguing. So you suspect that it is a lag on the cadence rather than output power which is causing this? I use the power meter for cadence so that would make sense. I’ll try fitting my Garmin cadence sensor and see what happens.


(Niel Jordaan) #4

I have the same problem - however mine takes much longer than 20-30 seconds to adjust, and, the resistance becomes so much that I actually battle to pedal. Not sure if I am doing something wrong? 


(Russell Gowers [CRANKS] KISS (C)) #5

Struggling to understand the downvotes on the original post…

As an update since the OP:

  • I changed trainer from the Flow to a direct-drive Elite Real Turbo Muin B+ which exhibits the same, or worse, behaviour

  • Then my power meter broke so I switched to using the trainer itself as a power meter. There is now no lag whatsoever - I can stay at a completely smooth xxx Watts at whatever wattage I choose.

So the issue is definitely latency over ANT+ between an external power meter, Zwift, and the trainer. Possibly the trainer has some kind of internal mechanism for maintaining wattage without having to call out over ANT+ except when a change is required?


(Niel Jordaan) #6

I dont have a power meter. I use the kickr snap as my smart trainer and obviously as my power meter.