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Tacx i-magic fortius , wattage & figures

1_reaper1_reaper Posts: 322
Hi all. Just back on the turbo turning the pedals after a work related accident. Been out of action since November. Only just started back this week. Using a Tacx Imagic Fortius . just wondered how accurate the wattage and other figures are. As only just started to use this type of Data. Just relied on average speed and timed routes before but now have this new toy so just wondered how accurate the figures are it puts out . Thanks


  • neebneeb Posts: 4,448
    It depends on a lot of things. There are reams of debate about this over on the tacx forum...

    You say the Imagic Fortius - is the brake device the fortius or the imagic? The fortius has the motor brake and is potentially more accurate I think. Confusingly, "fortius" is also the name of the earlier software for these devices, now replaced by "Tacx Trainer Software" (TTS). There are loads of bugs in the TTS software that potentially affect accuracy - I think the old fortius software is better in this respect.

    Accuracy out of the box may vary from one unit to the next - the only way to be sure is to calibrate it using a proper power meter. The error in the power readings may also not be linear, i.e. higher powers may be more inaccurate. Accuracy also changes throughout a run as the unit warms up - when its cold it underestimates wattage slightly and when its hot it may overestimate.

    All that said, if you always set it up the same way (same tyre & roller pressure), the tyre doesn't slip on the roller, and the suggested calibration value in the middle/end of a long run is within +/- 1 of the set value, I believe it can be pretty accurate, at least for average wattages on, say, a long climb.
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