16th March Update shows doubled power with speed sensor 2


I rode this week with my Garmin Speed Sensor 2 without a problem and the calculated power seems to match my usual experience in Zwift. Since yesterday’s update the calculated power is more or less doubled. Previous power of ~75 Watt (according to my feeling and selected gear) is now calculated with 150-200. I have tested with another Garmin Speed Sensor 2 and a different computer but the problem remains. It seems to be a bug with the new software version.

Anyone else with the same problem?

Hey, just tried to jump on for training session now, and exactly the same has happened to me. :sob:

I’ve rechecked my sensors against my fenix pro 6 and all seems to working correctly. Things go haywire when connected to Zwift.

Everything working perfectly prior to update.

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Yep, same for me, I have emailed Zwift support with a detailed review of my problems and photo’s of screenshots. All speed and cadence figures are correct when I’m in the sensor connection screen, and then go mental when I am in the actual riding part. VERY frustrated, as I can’t actually use it now ! Only way I will achieve 10w/kg though !Pic 1

Its the only way I’ll ever be able to ride at 600w. :laughing:

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It’s bonkers, I was registering over 1000W without trying ! Hope they fix this soon !

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Which trainer are you using? I suspect that Zwift have changed the power curve for Tacx Boost and Tacx Blue Matic (edit: and maybe Tacx Booster + Tacx Blue Motion, too) in this release - that could explain what you experience.

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Its an old Tacx thing, the orange one. Not had an issue with it before this update, figures were realistic to on road figures. If they have done as you suggest, I guess I will have to either buy a new trainer which I really don’t want to do (or see why I should !) or quit my membership and zwifting altogether. That would be a shame, as I have been quite enjoying it. Real issue is, not sure how I will know what has really happened, or when it may or may not be resolved. Frustrating.


I am using Tacx Blue Motion. I have not changed anything in comparison to the last two days but since the update it shows crazy power values for me (and probably wrong speed but I have no feeling for speed in Zwift).

Using the same, Tacx Blue Motion here.

I just hit 1100 watts on a Tacx Booster in setting 2, with the standard Tacx cadence and speed sensor, it normally maxes at 390.
To get close to normal I set the Booster to setting 6, but even then there is no way to ride below 100 Watts in a normal cadence like 85 RPM. My smallest gear is 32-21.
I guess all speed sensors are having the same issue.


Hey! Same problem here, Tacx Blue Matic with speed and cadence sensors would spike to 300W just waming up for a few seconds.

Hopefully they can patch it in the next few days or I’ll have to cancel my subscription.

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Same problem here, with Tacx Blue Motion.
It was working the day before the update.

I change to another trainer, and this is better, I can at least do my training… but my ftp test at the end will not be good…

Has anyone been able to solve the problem?

I think the only solution is if Zwift put the power curves for these trainers back to what they were before the update, as it is nothing to do with the hardware being used or the settings in the customers profiles. I hope they fix it soon !

Exactly same issue here on tacx booster. Speed in pairing screen looks normal and then all goes haywire with the power calc. Ruined ride today, thanks Zwift, I didn’t realise there was an issue with the power curves for these trainers!!! Please fix ASAP

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Yes, I have just updated and come on today and WOW, it’s giving me power that my on wheel Tacx Booster can’t do on Zwift (limited to just shy of 400 watts).
Is it the update?
Makes the ride somerhing of a joke.

Same for me, Tacx Bluematic is suddenly giving fantasy figures. Feels unusable at the moment.

Yep I had the same issues first thing this morning (on top of horrendous pairing problems). All worked fine last night pre update!

Yes similar problem here - Stagesbike SB20. At the end of my workout this morning I got suddenly 500-1000W for awhile. I had to stop the workout. FTP increased :)) Disconnected my SB20 from the power source and updated to the bike to the latest software. On my new try (same workout) it was a bit different; Wattage/RPM would drop and ERG mode disconnected for a few sec. Got it 3-4 times during a 45min workout…

I just hopped on for a cycle and had exact the same issues. I’m using the Garmin Speed Sensor 2 (with the cadence) and it’s registering ridiculously high power reading. It worked fine pre-update a few days ago.