Explain to me why zPower interprets my trainer's power curve differently than other software?

(Jon Elison KISS (B)) #1



I’m using zPower with a Cycleops Magneto trainer. I double checked that I have been using the correct trainer profile in Zwift. Now, my FTP has traditionally remained around 250ish. Trainerroad + Sufferfest workouts based at this FTP has always felt spot on - very hard, gruelingly doable.


My questions:

  1. During my first virtual race 2 weeks ago, Zwift recommended to me that my FTP should be 337 (based off my in-race 20 min average of 355 I guess). I’m all for improvement, but this seemed to good to be true.


I attempted a Sufferfest/TR workout at this FTP and made it no more than 25% through - rocked me. This workout also confirmed for me that the RPE I’m exerting in Zwift and TR are very different. Zwift is definitely interpreting it higher.


I have no Ant+ drop out (using an extender), correct trainer with what I assume is the correct and same power curve being applied in each software. Why is Zwift making me into a beast, and TR humbling me down to the struggling-for-form, new Dad I actually am?! Both are in theory using the same power curve and receiving the same Ant+ data…?



  1. Zwift zPower seems capped for me at around 450-500w. In TR, I am able to out virtual power as high as my effort can go (800-900w). So what gives here?


Is Zwift simply stopping at the edge of the power curve, while TR is possible running the same theoretical line extending further out (see chart)? If Zwift is reporting higher output than I’m giving, I feel like this is doubly limiting for me…


Any help is appreciated!