Taxc Flow calibration - idiots guide?

funny you should ask it 'cause I made a (late) discovery :o

I finally discovered this knob.

Believe me or not Bull, I'd say tighten it enough so it even becomes a bit difficult to unclip after the workout. And more important, don't even run any calibration tests. Calibration correction should remain to zero in my opinion. And you acheive this by doing as if you were to run a calibration test, but instead of hitting the "up" arrow (resulting in the word Speed to appear on the display), you press the "down" arrow (resulting in Zero to show on the display).

And by doing that, my Flow now reads only 20-30w over my Powertap values. That is much better than the 50-60w discrepency I use to get before I tighten this knob.

Each time a calibration test returns a positive value, the Flow will adapt its power calcualtion, thus reenforcing its main flaw : over-estimating the power ouptut you produce.

That sounds awesome...thanks! I'll give it a try. My motivation to get on the damn thing failed me tonight anyway 😎

is that 20-30w overestimation constant whether the value is 180w or 460w? or is the overestimation greater at higher values?

Each time a calibration test returns a positive value, the Flow will adapt its power calcualtion, thus reenforcing its main flaw : over-estimating the power ouptut you produce.[/QUOTE]

I put it on so tight that i can only just get the handle down when I push the roller against the tyre. any tighter and the handle cannot go fully down before the roller pushes against the tyre.

is this what you mean?

Sorry BullGod, I read this post a bit earlier in the day but intended answering it tonight after my trainer session.

That way I'll be able to tell you how tight very tight should be 🙂

But I don't think I made it this tight last time though. In fact I made my adjustments having this thread in mind...
http://www.cyclingforums.com/showpost.php?p=3056102&postcount=1

Especially this quote here

Quoted post said:

So once you achieve 100% friction, adding additional pressure between the tire and roller has no impact on the resistance level.

So once I was sure that the tire was "tight enough", I didn't try to tighten it any further.

Tonight I'm going to see how much room I really had and will report back tomorrow.

Cheers

Thanks.

I followed you advice on ignoring the calibration procedure and pressing the down button. This did seem to make my usual workout harder. For instance 10 minutes at 360w was surprisingly tough....and 5 mins at 420+ had me quickly at my max HR. Three of those and I had worked up quite a sweat.

My average for the first hour was 325 whereas when I was last using the trainer in the spring I would have expected 360...

basically it felt significantly harder.

BullGod said:

Thanks.

I followed you advice on ignoring the calibration procedure and pressing the down button. This did seem to make my usual workout harder. For instance 10 minutes at 360w was surprisingly tough....and 5 mins at 420+ had me quickly at my max HR. Three of those and I had worked up quite a sweat.

My average for the first hour was 325 whereas when I was last using the trainer in the spring I would have expected 360...

basically it felt significantly harder.

The calibration is to make sure that the resistance is the same everytime... so of course it was harder🙄 ... It has nothing to do with the calc of watt, a given wheelspeed/slope always gives the same watts, regardless the number of turns of the knob, but as you know now, the harder the tension (turns on the knob)the more you have to work...😄

Gees 🙁

I just realized that I forgot making a comparison between pt and flow at all levels. Sorry.

But as for how tight it was. Well by trying to tighten it just half a turn more, the screw got out of its socket 😄

So I was indeed at the limit. I don't know if it's good or bad, I'm going to continue testing the unit for accuracy under different tire resistance in the next couple of weeks.

And oh(!). Under 200w tonight, my flow was overestimating the power only by 10w, but at 260 it was around 20w over. So I guess we can say that it reads roughly 10% over at the moment.