By now everyone has either ridden or seen the new blue Tacx Flow trainers in our blue endurance training area. Feedback thus far has been great if only for the aesthetics of the new units.
There is an issue however that warrants a discussion to help people understand the units a bit more, that being the "accuracy" of the wattages reported by the units.
A critcism over the years regarding our older units were that they were "old" and beat up despite them in fact having all been maintained through the replacement of rear motor units, cables and computer heads. The only thing that was a mainstay from the first days of ETS classes were the Tacx aluminum "frames". In the first year we used them straight out of the box without any consideration as to their accuracy and real world applicablility. At races I would hear athletes speak of how they crushed our 5km time trials by riding in excess of 450W for 6-7min despite them remaining pack fodder in category 4/5 cycling races.
When I finally made the leap to a PowerTap hub direct force power meter (DFPM) I could finally work with "real" and consistent wattages reported through the strain guage technology embedded in the hubs. Long story made short, I performed a series of trials on randomly selected units while riding with the PowerTap wheel. I measured the power produced at the various slopes on the Tacx units in tandem with the power reported from the PowerTap and determined quickly that there was a vast difference in the reporting of power between the two units.
After many trials of changing the factory scaling in the Tacx computer and repeating the process, I was able to settle in on an acceptable range in which consistency was noted in the reported power for both units. The outcome was a reduction in the power that people were accustomed to riding at and a lot of "humbled" riders. In effect I helped to provide a more "real" world power perspective for people to train by. This was a shotgun blast to the ego for many.
Fast forward now to the past month and I have under gone the same process with several of the new units which I have calibrated to my Quarq Cinqo DFPM. This go around was less laborious for me as I was able to settle the scaling factor very quickly.
Now a few caveats to this.
First, I have noted a difference in reported wattages in the Tacx compared to the Quarq Cinqo if my inputted weight is not correct in the Tacx unit. My assumption then is for everyone to make sure they input "their" correct weight into the units and not my weight.
Second, the roll down calibration must be in the area of "0" to "+4" for the best results. So ensure that the correct pressure is applied to the rear wheel AND that you have 100psi in your rear tire. All my trials were constant at 100psi.
Finally, when doing short high intensity micro-bursts or intervals the reported average wattages will not be the same due to the reporting and recording average of the Tacx unit being slower than that of the sampling and recording rate of any DFPM. The DFPM is very sensitive to the application of force and will report near instantaneous wattage values - hence the reason to see such and up and down or on and off nature of power in a DFPM file.
When I performed a 3min and 20min time trial a few weeks ago, my 3min average wattage was 386W on the Tacx and 409W on the Cinqo. For the 20min time trial an average of 292W on the Tacx and an average of 294W on the Cinqo. I am quite happy with this result.
