FTP/Power/Speed seems incorrect

Hello! I’ve been riding on Zwift for about a year now. My FTP was in the mid 150w at that time. I had a good year training outdoors in a group and solo rides. Recently my FTP tested quite high (237w) and my speed also seems to have increased on Zwift rides. I haven’t changed anything in my settings or tech, so I’m wondering if there’s anything else I can do or check.

My tech:

  • Stages power meter (recalibrated last week and firmware updated)
  • Kinetic Road Machine trainer
  • MacBook Pro to connect to Zwift (and Strava)

Thanks for any guidance!

I am guessing that since you have been on Zwift for a long time you know how speed is calculated (Power, weight, elevation changes, in-game bike and in-game drafting). So if your power goes up (150 to 237) your speed within Zwift will also go up.

If you are asking if your numbers are correct, that would be difficult to answer. Did you calibrate your Stages before the test (not a week before, but right before)? Did you get similar power readings when riding IRL?


Hmm, I calibrated after the FTP test, so on second thought I should probably retest to see if the results are similar now that things have been recalibrated (and do it again immediately before the test for maximum accuracy).

I thought the power readings would still be accurate regardless of what the FTP calculation was. Is that not the case?

And I’m in Canada, so riding IRL isn’t a safe option for me right now!

Thanks for your fast reply Paul.

What was your power when you were riding IRL? Was it close to the 237 watts you tested at?

It doesn’t matter the FTP entered within Zwift before the test.

I just checked and my Garmin bike computer says 223w. Although I suspect it may have got to that level from summer drafting during group rides. I’m barely keeping my head above the water with my tech. It seemed more likely to me that my tech was off somehow than I’d advanced in my cycling so much!

I feel like if I do another FTP test (with calibration just prior), then I should accept those results as true. There wouldn’t be anything else to do, check, or adjust at that point, right?

The 223 is in the ballpark so the 237 is very possible to be correct. 

If there is any doubt doing a second one to verify the results would be my suggestion. I am guessing that the results will be similar since the Stages is a fairly accurate power meter and going from 150 to 237 is definitely within the realm of possibility within that time frame.

Well now that would be exciting to find it’s all me! Thanks so much for your input Paul. I will retest in the coming week and fingers crossed it all matches up or at least is resolved.