Tacx Flow - wierd tyre-related power issue

Discussion in 'Power Training' started by nmcgann, Sep 23, 2006.

  1. nmcgann

    nmcgann New Member

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    I recently got a Tacx Flow and set up my old steel road bike on it. It ate my 25mm Armadillo rear tyre within 2 weeks - it got very shiny and then developed 4-5cm splits down the middle with the rubber coming right away from the underlying fabric. It also ran hot and required a lot of roller tension to prevent it slipping. Also it spun down to a standstill very quickly (gave a high calibration number when doing the calibration routine).

    I just fitted one of the Conti trainer-specific 23mm tyres to replace the dead tyre. This requires much less roller tension to avoid slipping and takes quite a while to spin down (low calibration number).

    Now the odd thing is that I was doing 20min hard efforts on the old tyre at 200W - on the new tyre the equivalent amount of effort is reading 280-300W. Was the old tyre and it's very high roller tension eating the power difference?

    Neil
     
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  2. otb4evr

    otb4evr New Member

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    Neil,

    I don't have a the flow, I have an IMagic, but I also use this tire.

    I have noticed that it requires less tension on the roller to produce the same amount of wattage. How are you checking your wattage? I use a PT on my bike.

    My thought is that the regular tire was still slipping, regardless of the tension.

    BTW This will be my second season on this trainer-specific tire, and it still looks fairly new... ;)

    Jim
     
  3. nmcgann

    nmcgann New Member

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    I have no way of checking the Flow's absolute power measurement accuracy. I've seen comments that they over-read, but I'm looking for relative power increase as I train, so I don't think inaccuracy matters so long as it's repeatable.

    Neil
     
  4. SolarEnergy

    SolarEnergy New Member

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    Problem is that it's not 100% repeatable, but good enough to monitor your progression. You have to know that the inaccuracy will vary a lot depending on the cadence. Slope 4, 70rpm, my Flow underestimates power. At the highest slope, 80rpm, 340w, my flow is spot on. Slope 0, 100rpm, that's around 270w (on the flow's display) it overestimates it by around 40-50w.

    But again, it's a nice tool, good enough to monitor a progression, especially at a given cadence (with not too much fluctuation).
     
  5. otb4evr

    otb4evr New Member

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    Neil,

    To have some semblance of repeatabliity, you must warm up the tire and do a coast down on every ride.

    Even then, I know that the tacx measures too high going up a grade that is more than 4%, it measures too low when going down a grade that is less then 2% and it takes about 20 minutes to fully warm up.

    I didn't have a power tap until into my 2nd winter using the tacx, so I understand how much the unit helps keep one training through the winter, but also the flaws inherent in the system...

    Keep persevering and good luck...

    Jim
     
  6. SolarEnergy

    SolarEnergy New Member

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    The iMagic is much more accurate though. At least that's what I have heard.

    The interesting point is that I have heard that you can't ride the iMagic without connecting the cadence magnet. Well you can but the power is limited to 40w or something? Which leads me to believe that they use this number as a variable to perform their power calculation.
     
  7. vines

    vines New Member

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    I almost always use the iMagic without the cadence magnet and sensor attached. It works fine.
     
  8. Doublebiker

    Doublebiker New Member

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    Do you know that you are supposed to reagulate the tension based on the roll down test? The calibration number shall always be "0" when the tension is right.

    OTOH if u have a real PM then u might be able to set the calibration number to something else in order to get more accurate readings.
     
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