25 watts? That’s not a tad, that’s a tow truck. Even a 5 watt difference can have a big effect on your performance on Zwift, for example, a top ten finish vs. 30th+.
I love Zwift, and I really feel like I’m riding with others, but I always have to remind myself that it’s not representative of the real performance of others. In the real world, I’m much more successful with KOMs and segments. True, my local area isn’t as densely populated with riders from around the world, but it’s more than that.
Here are the issues:
Kickrs are inaccurate: My experience and that of many others is that the Kickr reads wattage about 25-30 watts too high compared to an actual calibrated power meter. I use an SRM, which is considered the gold standard. Out of the box, with repeated spindowns and using the calibration kit, I’ve had two Kickrs that verify this. 25-30 watts = ridiculous advantage on Zwift.
Estimated power is high. To test estimated power, I dug out my Kurt Kinetic and ran it on Zwift while also capturing the data from my SRM with a Garmin. At first, estimated power was about 50 avg. watts higher than the SRM. I was getting a lot of tire slip errors on that first trial, though, and I diagnosed that the issue was that the ANT+ stick was dropping out. On on the next trial, I moved the stick closer to the speed sensor and the errors stopped. The final result after several laps: Average estimated power was +8 watts higher than actual. Another very significant advantage.
I also have a Stages power meter on another bike and I get the same results.