I have a quite similar problem like op Craig Merrits.
I ride a Elite Real Power ant+ model. At The beginning, rpm an power ratio seem quite right. Resistance adaptment going up and down hills feels pretty accurate throughout the session, too.
But after some time, the resistance grows and grows on the trainer. I get down gear after gear to keep the rpm at the same level, to achieve the same power output. in the lowest gear, the resistance keeps on growing so strong, similarily to the displayed watts in the zwift programme, that my rpm need to go down to stay at my standard watts output.
Problem in short:
On even ground, no incline, same gear, same rpm but watts are going up and up wihtout peddaling faster. To keep up the wattage I would need to decrease rpm, or change gears down until no gear to shift is left.
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