The Race Power Calculator works best if there is a good variety of run types. For example, running inclines and descents, a variety of paces, different temperatures, windy conditions, etc.
When only running on the treadmill at 0% incline, the following apply:
1. The Race Power Calculator assumes your race is outdoor and that wind resistance affects your effort. If you only run on the treadmill (ie. no wind power), this will cause estimated race times to be faster than actual.
2. If you always run at 0% grade (or only a few other grades), Stryd does not have enough information if you load a racecourse that is not completely flat (and the predicted time will be off).
3. Running on a treadmill is different than running outdoor. Likely you can sustain a higher power outside that on the treadmill. The power target is correct if you are doing a race on the treadmill.
4. The temperature, elevation, and humidity are all set to 0, which does likely not reflect your actual running conditions.