Anybody have any reliable information on how accurate the watts are on the Tacx Flow trainer? If I calibrate it each session to adjust the braking pressure, does this ensure relatively accurate output? I don’t care if I’m a few watts north or south, but I want to be in the right ballpark.
Thanks,
Don.
First of all, what you get with the Tacx trainer is virtual power, and it all depends on the data that you entered, as far as your weight, age, and other info, so I don’t really think is that accurate.
My suggestion is, if you want more accurate power measurement, get an SRMor Powertap power meters.
I hope this helps.
I have an Imagic which uses the same resistance unit as the Flow. I have no idea how accurate the wattage numbers are, but they seem to be consistant for PE. If you want absolute numbers go with a powertap or SRM, but mine has benn consistant enough to get reliable workouts.
Hello
I would say the Tacx trainer is very accurate from session to session. What is in question is how precise it is in showing true power output, it believe it does have a percentage of error stat in it’s book. Since it is calibrated I would assume it’s quite close to true power. The only time I see this a problem is if you ride outside using another power device and want to compare numbers. But from riding session to session on the Tacx it should be very accurate.
Hope that helps,
Eric
I’ve always hoped my Tacx Flow is wrong. Otherwise I’m a lot weaker than I realized. 
As long as it is reasonably close I’m happy with that. As long as my 315W for an hour is within, say, +/-15W, that’s good enough for me.
I use the flow. When riding in 53/11 at 94 ave cadence I’m generating no way near 315 watts. How can that be?
Hello
I can tell you that if I ride a 53/11 on my Tacx at 94 rpm it’s way way above the 315.
It’s a matter of accuracy, if it always shows you 315 watts in a 53/11 @ 94rpm from session to session then that is fine. Because it is accurate for your training needs and will be able to use it as a tool to slowly increase your wattage output.
What I believe some people want to know is how precise the Tacx is in showing true watts. The only time true watts is a real issue is if you want to compare Tacx wattage to your watts when you ride outside using another device.
For training all you really need to know is the Tacx accurate from session to session so it can be used as a training tool.
Regards,
Eric
don’t know exactly how tacx “measures” power but all the ones like that I have looked at simply translate speed to power from a chart…rider ht, wt etc. shouldn’t be a factor in how much effort it takes to get a drum to spin at a certain speed…as said by another, it is always surprizing how slow you go on a trainer (how few watts you put out) because a trainer is always going to be slower than the road due to inertia of a rider on the road being so much greater than a 6lb fly wheel…seems the trainer is set-up to have a certain “spin down” that “mimicks the road” but does not mimck the ongoing inertia of a boby moving along the road…sort of weird that trainer speed and road speed seems so different, huh?
First off, I don’t have and have never used a Tacx Flow, so my following comments may not be applicable. However, amongst the many trainers i do have or have had, i have a Tacx Excel and a Grand Excel (i think these may have been the forerunner of the Flow, but i’m not certain).
Anyway, I’ve extensively used my trainers and compared the power that is estimated from those with the power that is recorded from my Power Taps and SRM. I have found that my Tacx units aren’t very accurate, and the error changes as the intensity of the session changes (for e.g., it may be a 5% error at 200 W and a 10 % error at 400 W).
Additionally, as the session drags on, the power that the Tacx records changes as the braking unit heats up, this lessens the resistance. For e.g., after 20-mins my Tacx my say 220 W while my PT says 230 W. After an hour the Tacx could be reporting 250+ W, while maintaining a constant 230 W (on PT/SRM).
Finally, it appears that each individual Tacx unit estimates a different power for a given actual power. For e.g., i’ve ridden more than several Tacx units, and each one gives a different power reading for the same actual power (as recorded by my PT and SRM).
None of this is meant to be denegrating to Tacx. I continue to use Tacx trainers quite a lot for training on, and the issues i’ve pointed out are common to most trainers that you can purchase.
Just to reiterate, these data weren’t collected on a Flow, and the braking unit could be completely different?
Ric
Hey Rick, thanks for that info. I just want to make sure I’m not being ridiculous when I claim that I’m holding 315W for an hour. I’ve never used any power meters so it’s difficult to compare it to anything else. If I’m within around 15W of that, that’s good enough for me. One thing that seems to improve accuracy of the Flow is to calibrate the unit every single time you use it, after “warming up” the brake for 3-5min.
Try calibrating the unit every time you use it. The instructions are in the manual.
Based on what i’ve seen from Tacx (non Flow) trainers, and what if memory serves me correctly someone on the wattage forum reported last year or the year before, it’s unlikely that you’re riding at 315 W (simply because they don’t seem to be accurate).
I don’t know how close you would like it to be to consider it accurate. But bear in mind (at least with my Tacx’s) that what starts out at one power, will be a power by the end of an hour.
Ric