Resistance delays


I run group workouts on Zwift so the group is running a variety of trainers, wheel on & direct smart trainers and a whole variety of manufacturers.

I see a couple fo consistent behaviors that I would love to be able to answer for the group that I do hope everyone can help with.

  1. When in ERG mode, most experience a delay in trainer resistance adjustment on the transition of intervals. I have a Hammer 3 and I notice 2/3 sec delay after crossing the interval. While manageable, I am not sure whether this is an expected behavior.

  2. When in ERG mode, other riders who have a lot of experience with Trainer road complain that ERG mode is not as stable in Zwift. TrainerRoad is very steady with little fluctuation in power, and in Zwift the power fluctuates a lot more and adjustments in resistance seem to be delayed.

These two behaviors seem to be related.

I speculate that given 1) the connectivity (Bluetooth or Ant+) are the same for each users and 2) the trainers are all running the same firmware they were running when connected to TrainerRoad, that there has to be something else.


  1. Related to internet & wifi connectivity? I imagine Zwift is much more connectivity heavy than trainer road.
  2. Related to processor speed on the computer device, ipad etc. (Given Zwift ids more graphically heavy)


I use Wahoo Kickr Bike. There are two sliders for 3 seconds power smoothing, one in Wahoo Fitness app on the phone, hidden somewhere in Kickr Bike parameters, and the second one in Zwift. My observation has been that the slider in Wahoo app is much more powerful. When it is turned on, you get a perfectly straight power line when you are riding intervals in ERG mode, and you also get a smooth (you can say, spread over those 3 seconds) increase or decrease in power and resistance. BTW, this is uploaded to the trainer during configuration process and is stored there, one does not need to have Wahoo app open or connected to trainer (unless one wants to change this setting).

If you turn this slider off, you will get a lot more noise on the power line, but faster transitions.

The slider in Zwift, in user configuration menu, has presumably a similar but I think somewhat less visible behavior.

The bottom line, I believe it is neither of your guesses but configuration of the trainer and Zwift. Some trainers may have this configurable, some perhaps hard coded.