HUB Power accuracy suddenly off despite calibration

Dear all,

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.

Hi, can I ask if you found a fix for this at all please? It sounds fairly similar to what I had yesterday, and I’m pretty sure it’s the firmware update which caused the sudden change. Thank you!

Hi James,

Yes, after I was completely ignored by Zwift support, here was my fix: got a refund and bought a Neo 2. Really worth the money, very reliable and precise.

Zwift support was a complete disaster. They were very polite and friendly, however completely useless. I sent them logs with my power meter from my Garmin to compare etc… no answer at all.

Either they have some units which are somehow defect or it is a design flaw. Either way I did not want to loose time therefore got a refund.

I hope you will find something that works out for you.


I am having the same issues here.
Garmin powermeters read a lot lower suddenly then the Hub.
Training on the Hub has been awful since a couple of weeks.
Reached out to support and hope I will be helped.