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F945 and Tacx Flux 2 Smart (t2980) - same workout (ftp/power/cadence) - but F945 vs F945 different speed reading

Hi Guys,

I am a happy owner of both the F945 and a Tacx Flux 2 Smart. And I use the F945 as the central single truth for recording the Tacx activities. Paired the Tacx and the F945 via ANT (all default settings).

Reading these forums I understand Garmin/Tacx are working hard to improve the alignment of the software ecosystem. I hope they will manage as that is why I invested in this Garmin product family.

In the meantime I hope that someone has similar experiences and perhaps tips for me.

Using the TacxApp I "programmed" a reasonably steady power workout (endurance building similar to "Endurance 3" in RGT).

Strange thing is that doing the same workout today (same FTP, power setting, and doing about the same cadence) the F945 noted overall a structural lower speed compared to earlier sessions (typical e.g. 19kmh vs. 26kmh). So this is a F945 to F945 comparison and not about difference between the Tacx App and de F945 reading. Yes I know Ceteris Paribus, and I double checked the readings in GC. (I do know different from last session was an Android update causing issues with GC that needed to be resolved with emptying the cache).

Questions:
1. Anyone having similar setup and ditto experiences? Any tips?
2. Currently in the F945 the sensor wheel size setting, is set to automatic. I have a gut feeling that this has something to do with it, as once earlier the watch messaged that it detected a wheel size. However after that I reinstalled the Tacx sensor on the F945 again and left to defaults (which is automatic and no calibration messages). In the Tacx App you can find the wheelsize, so I am considering to put that value in the watch and see what the result will be...Anyone experiences with this?

NB1: According to the Tacx utility App I have the latest firmware. I also have the latest auto-pushed F945 firmware.

NB2: Furthermore annoying that during the latest workout a Garmin Connect permission request on the phone crashed the Tacx App and so aborted the workout after 50'. (Speed readings were already off from the start).

0 Dr Phil over 5 years ago

When training indoors you need to change the wheel size setting to manual and input the appropriate wheel size. When set to automatic the wheel size setting is dependant on GPS to set, which if you do manage to get when inside is not going to be that good. I do have GPS set to off for indoor training anyway.

This came up a week or two back and prompted me to look at my settings. I use Rouvy to transmit the activity to Strava and record on my 945 to send to Garmin. Rouvy uses the CNS from the Tacx trainer for speed and cadence whereas my 945 uses the bike's speed and cadence sensors. I checked then to ensure the wheel size settings were consistent between the two.

0 mcalista over 5 years ago

With direct drive trainers such as the Flux, "speed" is very much dependent on which gear you are in. Hold your cadence and power steady, and watch as your reported "speed" increases as you switch to successively higher gears, as the rate of axle rotation increases,

And honestly, I don't know why speed matters on an indoor trainer - it is an irrelevant. You are still sitting in your pain cave and have gone nowhere at zero speed. Full disclosure - I use the same bike indoors and outdoors, and use mileage to track drivetrain maintenance intervals, so I like to have indoor distance (and therefore speed) in roughly the same ballpark, and choose a gear that gives a speed roughly matches what I could expect riding outdoors at that power.