Tire pressure and trainer resistance



  • Hi there,
    This has always bugged me and I'd like to hear your thoughts: assuming the tire pressure is always the same, is power curve affected if the resistance roller is tightened 1 complete turn vs. 3 complete turns?

    Example day 1: tire pressure 95 PSI, CycleOps Fluid2 roller tightened 1 complete revolution

    Example day 2: tire pressure 95 PSI, CycleOps Fluid2 roller tightened 2.5 revolutions.

    Will day 2 create a higher power output if I'm spinning at 80 RPM because there's more pressure on the tire?



  • Hey Miguel,
    Yes Resistance applied by your Trainer on your rear wheel will affect the power curve calculation.
    That is why it is important to keep the same number of knob turn on your rear wheel.

    For example, Kurt Kinetic states that you should set it from 3 to 5 turns to have a good match.
    Remember that Power Curves are not 100% reliable, some curves are more reliable than others to estimate your power. For example, the KK road machine is a really good curve, it has been tested and compared with Power Meter data and both are really close.

    Best thing you can do is keep your knob turn the same between sessions. That way at least your power numbers will be reliable from session to session, even if it's not your exact power, it's still a good tool to base your Workout difficulty on and see your progress.

    Max



  • @Miguel,
    And I'll add. As far as the system knows its is going x mph which = y watts. But changing the tension does change the resistance that you feel. If you had a power meter, it is upstream of the roller/resistance unit and would show that you would require more power to go x mph when more tension is applied. It's been posted on forums that doing a coast down check is the best way to keep the tolerance narrow. I have a KK fluid trainer, I read about and started doing a coast down check many years ago. KK has published their resistance curve and based on guys with power meters they found the following: When the unit is cold spin up to 20 to 20.2 mph and coast while timing with a simple digital watch the number of seconds it takes for the wheel to stop. Cold it would take ~12 seconds to stop spinning, after ~10' of riding the unit is considered warmed up and if you do another coast down check it would take ~2 seconds longer to stop. This ~14 sec coast down time was found to be about the same as the KK published power curve based on power meter readings. Now with the COF2 trainer, not sure what the coast down time should be but if you felt a certain setup feels right then do the coast down and make sure it's in a tight range so that ride A vs B vs C and so on are all comparable to one another. This way the gains are all relative and will show up on the road.


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