Tacx Flow turbo trainer

16simon

Hi all, I'm looking for a turbo trainer with power measuring that I can use this winter (or this week even, unless the weather improves), and I can get a 2nd hand Tacx Flow. Some internet research shows that it might have some problems around measuring power accurately, and possibly also around measuring consistently.

Has anyone tried one of these? Is it worth a go, or is it not sufficiently accurate to be useful?

phreak

I've got one of these. I don't know about accuracy as I have nothing to compare it to but the speed is similar to that provided by my normal bike computer. To be honest I don't mind too much how accurate it is as long as it's consistent, which it appears to be. I've been very happy with mine.

liversedge

Got rid of mine - as your speed increases the power becomes less and less trustworthy. But for the price you can't complain really.

phreak

liversedge wrote:

Got rid of mine - as your speed increases the power becomes less and less trustworthy. But for the price you can't complain really.

Could you elaborate?

liversedge

When setting a target wattage it gets progressively easier as you increase speed and vice versa as you increase speed the wattage goes up. I checked against a Powertap and it was off by *a lot* as wheel speed got higher.

Secondly, calibration was inconsistent even with a conti turbo tire and inflated tyres to 100PSI and careful push on. Somtimes at 18mph it would be very close and at other times it would be waaay off.

In the end I forked out for a computrainer,

phreak

That's odd. My wattage has been very consistent with the speeds shown, both on the tacx computer and my own bike computer. That's at speeds of 35-40km/hr. I'm not fussed about doing short spring work so that suits me fine.

I know online calculators are not ideal, but just checked a watt/speed prediction and it seems that the wattage I average is underestimated if anything, ie it should see me going quicker than the Tacx is suggesting. I can handle that.

To be honest though as long as it's consistent, that's all you need surely?

16simon

Hmmm... this is the problem. It seems that when it's compared to another power measuring device, it is not consistent... I don't know.... I've been offered a good price but I think that I'd be better off saving my money for something better if it isn't accurate.

liversedge

phreak wrote:

That's odd. My wattage has been very consistent with the speeds shown, both on the tacx computer and my own bike computer. That's at speeds of 35-40km/hr. I'm not fussed about doing short spring work so that suits me fine.

I know online calculators are not ideal, but just checked a watt/speed prediction and it seems that the wattage I average is underestimated if anything, ie it should see me going quicker than the Tacx is suggesting. I can handle that.

To be honest though as long as it's consistent, that's all you need surely?

Speed was accurate and consistent. Wattage was neither accurate or consistent.

RChung

liversedge wrote:

Speed was accurate and consistent. Wattage was neither accurate or consistent.

As Mark said, speed is accurate and consistent. I found wattage to be consistent but horribly, terribly, abominably inaccurate.

In this plot, the red dots were collected several months after the black dots, which indicates the speed vs. watts reported by the Flow was consistent.


However, this plot shows that the "ergo" wattage was unusably inaccurate:

Mccaria

I have had the Tacx Flow for 18 months+ and have used it as a mainstay of my training. I had 2 problems when using the wattage function as a training system.

Firstly the wattage can move around notably - so if I try to keep a consistent wattage of 250 for 5 minutes the wattage will move in a range of 225-250 with no change in cadence or resistance. This is frustrating if you are trying to use the wattage function to set target training zones (imagine doing a training session where you increase power by 25 watts every few minutes, when the wattage reading can vary by 25-30 watts).

Also initially I was struggling to hit target wattages on the TF for my training programme. Eventually I bought a Powertap wheel which I use on the TF. Comparing the wattage output, the wattage from the TF is at least 10% lower than the Powertap (on wattage output in the 200-250 watts range). I am pretty sure the Powertap is accurate (not just because it gives the higher reading !) as it is close to the expected outputs and is consistent to data from my coaches SRM system.

The TF gives consistent output ie for a given resistance and cadence it gives the same wattage numbers each time, but it is not a consistent differential to the powertap (ie at 200-250 watts the difference is circa 10% but the % differential increases as the wattage output increases.

So if you wish to use the TF to gauge your own progress then it will do this, but it does not compare accurately to the wattages given by other systems Powertap/SRM etc so you need to be careful if using wattages from other systems in setting training programmes or comparing your performance to others.

By the way Tacx has a totally justified bad reputation for dealing with customer enquiries. Sending them emails trying to understand the wattage variability and differential has proven to be a complete waste of time

16simon

Thanks everyone. I didn't buy it as it seems like it has too many problems with accurately and consistently measuring power. Has anyone got any recommendations for a turbo that measures power accurately?

andyxm

Buy a powertap / SRM then you can measure accurately on the trainer and when you are out riding, I'm not sure any trainer would be better than that.

nmcgann

16simon wrote:

Thanks everyone. I didn't buy it as it seems like it has too many problems with accurately and consistently measuring power. Has anyone got any recommendations for a turbo that measures power accurately?

Any cheap turbo plus a powertap wheel system (an older wired system is fine). Any other option is either less accurate or at least as expensive.

Plus the ptap can be used out on the road.

The Flow is still a good turbo though - just not an accurate power measuring tool.

16simon

Thanks for the advice, but I've already got a Powertap wheel. I don't like to use my outdoor tyre on the trainer as it wears the surface of the tyre smooth.

I've got a Cyclops fluid turbo, which does the job fine, and I stick an old wheel with a worn tyre in the bike when I'm using it. Since I'm measuring power on the road, it would be nice to be able to do this when I'm riding indoors as well.

nmcgann

16simon wrote:

Thanks for the advice, but I've already got a Powertap wheel. I don't like to use my outdoor tyre on the trainer as it wears the surface of the tyre smooth.

I've got a Cyclops fluid turbo, which does the job fine, and I stick an old wheel with a worn tyre in the bike when I'm using it. Since I'm measuring power on the road, it would be nice to be able to do this when I'm riding indoors as well.

Why not just swap the tyre on the ptap wheel before using it on the turbo? Before I got a 2nd ptap wheel that is what I did - during the winter weekday sessions are all on the turbo and then sat+sun is all road, so it was only a couple of tyre changes a week which is tedious, but do-able.