I got my brand new Zwift hub last week and was delighted. However, today, I ran into trouble with the power accuracy. Let me summarize:
- This summer I managed to pull 292W over 11mns on a hill close to my home town, this is not a 20mn FTP test, so taking around 90% instead of 95% gave me 262W FTP. I use a Garmin Rally power meter on my bike.
- I continuously trained since then and am pretty sure I did not lose fitness.
- When I got my Hub last week, I started with an FTP test. I knew roughly my FTP from my summer test, so I aimed for 280W over 20mns. I managed 278W (finishing at 190 pulses at 40 years old, I paced it perfectly). That gave me an FTP of 264W. All good. It matches what I know.
- Then I started the FTP Builder program. All was going well. Finished the first week.
- Today I started the second week with the tempo program. It asks for 230W during the “high intensity” segments (same as the first week tempo session). And there I noticed I was struggling, it was much harder than the first week. My first tempo session from week 1 had my heart rate around 150 at 230W, but then today I had to go above 170 pulses! Insane. So I realized the power from the Hub must be off.
- I installed my Garmin Rally power meter on the second bike I use for the Hub and made a short 230W ERG session while recording it with my Garmin Edge. Result: The hub pretends I am at 230W, but the Garmin gives me figures above 250W! That is 10% off!
I updated the firmware, and recalibrated (like 5 times or more…), impossible to get back to the initial power feeling and accuracy from the first week.
What shall I do?
Thanks in advance for your help.