Tacx flow calibration issues



bullyboy

New Member
Dec 5, 2010
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I have purchased a tacx flow so i can use power to train with in the long winter months in the north of the uk.
When the device is calibrated i think it measures how long the wheel takes to slow down and gives you a reading from a negative number through to positive numbers. Negative numbers mean the runner is less tight against the wheel and and positive number means the runner is on the tight side against the tyre.
Now even though the tyre pressure is always the same and how tight the runner is against the wheel is always the same I get different readings when calibrating.
I always do 15-20 mins warmup and then calibrate.
Now if the setting comes out as + 5 for eg do i need to slacken off the runner until it gets close to zero as possible?
If i do then the tyre slips.
Also if I get a different reading for calibration each time but ride @ say 300W (I wish) does it mean the 300W pertains to the calibration setting or does it mean i may be putting in more or less effort to turn the pedals at a set power. In otherwords is 300W really 300W what ever the calibration setting?

anyone ideas would be great!

bullboy /img/vbsmilies/smilies/hissyfit.gif
 

RChung

New Member
Sep 12, 2006
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My experience with the Flow is quite old so I don't know if Tacx has fixed the problems with it since it was first released. However, back then I did a fair number of tests on the Flow against a statically checked Power Tap. The good news is that when the Tacx rolldown calibration number was held constant, over a several month period the Flow read consistently. The bad news is that it was consistently off, especially in erg mode. In addition, I tried altering the scale factor, the rolldown calibration (i.e., the roller-to-tire pressure), and the mains wattage and was unable to get the Flow to read accurately.

[Edit:] You don't need to keep the rolldown calibration at zero.
 

bing181

New Member
Oct 23, 2004
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16
i do a roll-down calibration every week or two to make sure it's still 'on' - I also check at the end of a session when the tyre is warm. I've never had any problem adjusting the pressure to get a reading around zero.

On the other hand, I've found the Flow VERY picky in relation to tyres. In the same setup, same wheels etc., and with proper calibration, it will display up to 50 watts difference for the same output, depending on the tyre I use.

FWIW, i've found Continental GP 4000s pretty good at keeping things honest.

In other words, get the grippiest tyre you can, and that slipping rear wheel may be a thing of the past. Just my experience.
 

cheetahmk7

Well-Known Member
Sep 16, 2010
844
85
28
Originally Posted by bullyboy .

I have purchased a tacx flow so i can use power to train with in the long winter months in the north of the uk.
When the device is calibrated i think it measures how long the wheel takes to slow down and gives you a reading from a negative number through to positive numbers. Negative numbers mean the runner is less tight against the wheel and and positive number means the runner is on the tight side against the tyre.
Now even though the tyre pressure is always the same and how tight the runner is against the wheel is always the same I get different readings when calibrating.
I always do 15-20 mins warmup and then calibrate.
Now if the setting comes out as + 5 for eg do i need to slacken off the runner until it gets close to zero as possible?
If i do then the tyre slips.
Also if I get a different reading for calibration each time but ride @ say 300W (I wish) does it mean the 300W pertains to the calibration setting or does it mean i may be putting in more or less effort to turn the pedals at a set power. In otherwords is 300W really 300W what ever the calibration setting?

anyone ideas would be great!

bullboy /img/vbsmilies/smilies/hissyfit.gif

I have a TACX flow as well as a SRM and here are my observations.

If I set the tyre pressure to 100 PSI, I do the roll down calibration after 10 minutes of riding, I adjust the knob to get a reading of "0", and I always ride my efforts in the 53 x 12, then the ergo mode is very consistent for not just the training session, but from month to month.

I use a bright orange indoor specific tyre for all my indoor workouts. I haven't been experiencing tyre slip and the tyre is wearing so slowly that the wear is almost imperceptible.

If when doing the roll down calibration, I don't adjust it to get a reading of "0", the ergo mode will read differently. If you were to experience tyre slip, you could set the knob to a different value that doesn't experience tyre slip, but make sure you always strive for that value as consistency is what you need.

The TACX flow is around 50 watts optimistic when set to 350 in the ergo mode, although the lower my cadence the less optimistic the Tacx is.
 

bullyboy

New Member
Dec 5, 2010
3
0
0
Interesting input. Can I just ask what you mean by 50W optimistic?

If I leave my calibration as +3 then will this produce an innacurate power reading, in other words a higher power than your effort suggests?

/img/vbsmilies/smilies/biggrin.gif
 

tonyzackery

Active Member
Dec 23, 2006
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Forget the gyrations. Sell and get what you can for the Tacx, and then parlay that on a "real", practical ergometer - the Computrainer. No this isn't an ad - heck, I don't even own one, but I've used them enough to know they're light-years better (read: accurate, consistent, reliable) than any of the "wannabes", aka Tacx and Elite. FWIW, I own an Elite Real Axiom and for what I ask of it - varying terrain tempo and endurance riding - it's great as it breaks the monotony, but I also have a PT so I don't care about the wattage numbers the Elite is telling me. To be honest, they're practically worthless, and that's even against itself as the thing takes about 20 minutes to stabilize due to the combined usage of fluid and magnetism to provide resistance.
My $0.02CAN worth...
 

cheetahmk7

Well-Known Member
Sep 16, 2010
844
85
28
Originally Posted by bullyboy .

Interesting input. Can I just ask what you mean by 50W optimistic?

If I leave my calibration as +3 then will this produce an innacurate power reading, in other words a higher power than your effort suggests?

/img/vbsmilies/smilies/biggrin.gif

My TACX Flow reads 350 Watts when my SRM reads 300.

I found for different cal number ie +3 or -3, the readings I saw on my SRM varied. I can't remember which way, just that you are best to set it to the same value every time.
 

cheetahmk7

Well-Known Member
Sep 16, 2010
844
85
28
Originally Posted by tonyzackery .

Forget the gyrations. Sell and get what you can for the Tacx, and then parlay that on a "real", practical ergometer - the Computrainer. No this isn't an ad - heck, I don't even own one, but I've used them enough to know they're light-years better (read: accurate, consistent, reliable) than any of the "wannabes", aka Tacx and Elite. FWIW, I own an Elite Real Axiom and for what I ask of it - varying terrain tempo and endurance riding - it's great as it breaks the monotony, but I also have a PT so I don't care about the wattage numbers the Elite is telling me. To be honest, they're practically worthless, and that's even against itself as the thing takes about 20 minutes to stabilize due to the combined usage of fluid and magnetism to provide resistance.
My $0.02CAN worth...

Or keep the Tacx and put the remaining $2000 towards a power meter.