Over the years, many athletes have become frustrated with the difference between inside and outside perceived effort. During my years in Colorado at CTS, we often heard from athletes how it felt so much harder to ride on the then-popular Cycleops Fluid Trainer. As a result, several other coaches and I began to look into why that may be. Comparing crank-based power meter and hub-based power data, the one variable we noted was that hub torque, when compared to crank torque, significantly increased when indoors vs. outdoors. Ultimately, due to time, and other priorities taking precedence, we concluded that it was likely due to the difference in momentum/wheel speed.
With smart trainers, many athletes say their power indoors and outdoors has a different perceived effort. As coaches, we want to make sure we compare apples to apples. There is always a slight variability in power data collection, and we want to ensure that your power numbers always come from the same device. Because of this, we want to ensure you select the proper power source.
When you log in to Zwift, a prompt will ask you to select a “Power Source” this is the device that will determine how the trainer responds to your efforts. We recommend that our athletes use the power meter on their bikes for the power source. By doing this, we know that the data that we are receiving will be from a consistent device, whether you are indoors or outdoors.
It may sound silly because most trainers, and power meters boast a +/- 1% accuracy, but we have seen variability of up to 10% in trainers of all brands and among the same brand when using the same power meter.