I haven’t used my Tacx Flow for a while now, but there are two main modes – Slope mode which allows you to set a particular resistance (such as +2) and Ergo mode which allows you to set a particular wattage and it will then stick at that wattage whatever cadence you are pedalling at. I’m assuming you are using the former of these?

I don’t think the the unit should change your settings all the time and an Ftp of 218 at 56kg is pretty good (that put you at around 3.89w/kg). This sounds fine if you are a fairly strong cyclist, but with older units like this you can’t really compare it to other readings so I wouldn’t worry too much about the actual numbers. What you want to be able to do though is make sure that those numbers are the same from ride to ride that you do so that intervals etc are repeatable and you can see if you are improving. I don’t know why you are having such a discrepancy from one ride to another. My Tacx Flow was always consistent even if the actual numbers it gave me weren’t very accurate.

Alan.

No problem Rob, glad to be of assistance.

As far as I’m concerned as long as I’m not getting any slippage on the rear wheel then I don’t see the need to have the contact pressure too high.

I’m planning a horrible interval session for this afternoon. 7 reps of 1 min @ 400 Watts and 4 mins @ 100 Watts… It was pretty hard last time I tried it about a month ago so we’ll see how I go!

Al.

not having as much contact pressure has brought the calibration figure
down.

many thanks for the input!

Rob.

Hi Rob,
Hope you’re happy with the Tacx Flow, I’m still loving mine, although the new tyre does make quite a loud whistling noise on it so I don’t know what my wife will think of that!

As far as calibration goes, then I’m no expert on it, but as long as your calibration values are usually within the same range then I guess that will be fine. Those figures sound OK, and I’ve seen that many people have values somewhere between +10 and +15 when calibrating their machines. A quick look on the Tacx forums confirms this.

I leave my bike set up on the turbo trainer all of the time. This means that there is very little that changes between one session and the next so I don’t calibrate every time. it would also explain why my calibration values are always the same (until I changed the tyre this week). If however you take the bike off the machine in between session and then use it on the road it is likely that the readings will vary to some degree as many things could have changed. Tyre pressures and the amount of contact between the tyre and the roller being the main contributors.

You may find that if you release the pressure between the roller and the tyre slightly then your calibration figures will drop closer to 0. I don’t think this is necessarily something to aim for, but you might have too much pressure between the two so a bit of experimentation wouldn’t go amiss. I have mine set up so that there is a little bit of slippage between the two when I first start pedalling, but once I’m into a rhythm or a decent cadence then it is fine.

The other thing to note is that the Tacx Flow instructions say: “To optimise the Flow’s calibration we recommend cycling for at least three minutes to enable the brake unit to warm up”. It is therefore possible that differences in the ‘warm up’ before doing a calibration could affect the figures you are getting.

As far as I know the calibration figures are used by the computer in the Tacx flow to adjust the power output (wattage) readings so that they stay consistent from session to session. It will never be perfect on a machine at this price point*, but the fact that it has calibration and that your figures vary a little from session to session should mean that consistency between your workouts is greater than it would be without the calibration settings. If you didn’t (or couldn’t) calibrate then there would be no compensation being made for differences in resistance due to tyre/contact pressures.

I wouldn’t worry too much about the exact figures, the important thing is that they are usually in the same ballpark and that you do calibrate if anything changes (or you take the bike off the machine) so that the machine can compensate for these variations. You may want to experiment a little with the contact pressure between the tyre and the roller though just to see how this affects the calibration settings and the feel of the machine.

From my experiences so far and what I’ve read elsewhere, the exact power output readings on the Tacx aren’t necessarily accurate (when compared to other power meters) but they are at least consistent which is the important factor as it allows you to replicate your efforts on the same machine. The calibration feature helps with this consistency.

Hope that helps, and let us know how you get on.

Al.

*Machines that they use in sports and exercise labs that do need to be scientifically accurate cost tens of thousands!

Just bought the flow trainer but confused on calibration set up
and wondered if you could help?
followed the instructions for calibration which has given me
readings of between +9 and +13! does it need to be as close to 0
as possible and if so how do you change the calibration figure?
also, do you need to calibrate every session?

hope the questions make sense!

cheers.

rob.