How realistic is ride to GPX?

Hi all,

I've recently bought a Tacx Flux S trainer and am really enjoying the smart trainer experience. I have a suspicion that the measured power is too high. I don't have a power meter so can't verify that. One thing that makes me doubt the power measurement is this:

I did a ride to GPX workout on the Tacx Desktop App, I uploaded a gpx file of a route that I do sometimes IRL. It's a 44 km route with around 800m elevation. I completed the virtual ride a lot quicker than the real ride ride: 1 hour 32 mins vs 1 hour 54 mins. I understand that it will be never be exactly the same time as in the virtual ride there is no breaking for corners and traffic and no wind, but I didn't expect the difference to be this big. Does anybody have a similar experience?


avg speed 28.6 km/h

avg heart rate: 126 bpm


avg 23.3 km/h

avg heart rate 140 bpm

So to me that looks as if the real ride took more effort but was slower.

Obviously I have calibrated the trainer. Trainer difficulty is at 100%

  • I haven't had a lot of time on my Flux yet but previously pretty happy with a Flow. Using the Training App (phone or computer) the "speed" is derived ("gameified" / virtual) from the measured power and the current grade and not a direct measurement and thus speed is overstated because you don't have to brake due to corners or road conditions etc. The "speed" going down a hill on the Flux would be enough to scare me if on the road, probably often twice what I might achieve for the same real life ride, 70+kph not unusual whereas 40 would generally have me reaching for the brake.

    At the same time the trainer resistance can only go down to the equivalent of a 0% grade (not zero resistance) for flat or downhill sections (no negative resistance, no gravity assist) and on my Flux this seems higher than on a real flat or downhill and thus the trainer seems (don't have HRM) like more effort?

    The simulation is pretty close for uphill though, with my Garmin I often compare a recorded (uphill) real ride to the same re-ridden on the trainer and they are close (Trainer still a bit generous though)

    I don't have a Tacx subscription so limited to the demo GPX rides if using the app.

    Riding a GPX with the Garmin is a lot harder as the base resistance (0% grade) seems higher and no "gameified" speed means I am hard pressed to get to 25kph on flat or downhill and the uphill is a little more generous than with the app.

  • The observed differences between virtual and real rides on your Tacx Flux S trainer likely stem from various factors, including the absence of real-world variables like wind and terrain changes in the virtual environment.

    Calibration helps but may not eliminate all discrepancies. Additionally, the "100%" trainer difficulty setting can make virtual rides more challenging, but it doesn't precisely mimic real-world conditions.

    Consequently, the virtual ride may feel easier with a higher average speed and lower heart rate. To align both experiences better, consider adjusting trainer difficulty settings or using real-world cues as your baseline for effort during virtual rides.