Edit: The problem was fixed in Zwift version 1.0.6541 released 2021-03-23
With the update Wednesday to game version 1.0.64913 many – like really many – have suddenly experienced crazy power numbers when using one of these trainers:
- Tacx Boost
- Tacx Booster
- Tacx Blue Matic
- Tacx Blue Motion
The problem is not with your speed sensor, nor the trainer itself, but Zwift introduced a bug. It changed the power curve which is defined in-game and used to translate speed to power.
We’ll have to wait for Zwift to fix it for real but in the meantime you can get riding with realistic number simply by selecting a different trainer model from the list in the pairing screen.
I dug into the defined power curves and found what seems to be fairly close matches:
- Choose Jetblack M5 Mag Pro instead of Tacx Boost
- Choose Tacx Blue Twist instead of Tacx Booster
- Choose Jetblack M5 Mag Pro instead of Tacx Blue Matic
- Choose Minoura MagRide-60 instead Tacx Blue Motion
Simply choose the alternative trainer instead of your Tacx when pairing (but remember to let the trainer resistance setting be the same as always for your Tacx – simply ignore what Zwift says it should be for the alternative trainer).
Here are the power curves so you can see how they compare. The graphs show power (watt) as a function of speed (mph) – how much power Zwift calculates you are putting into the pedals based on the speed of your rear wheel: