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Head winds & Power Tap

mcstrangelovemcstrangelove
in General Training Discussions

I've gotten pretty good at knowing how much pedal pressure = how many watts….whether it's flats, climbing, fatigued or fresh.  The problem is head winds.  If I'm riding into the wind and mashing the pedals (z4-5 pressure), I'll look down and see z1-2 on the Joule.  Happens every time.  

 

I've calibrated the thing, new batts, talked to CycleOps/Saris.  Everything is working right.  Just wondering if there is some weird phenomenon with the PT when it comes to head winds…or maybe it is totally in my head (?).

Comments

  • mgraffeomgraffeo
    how does your cadence change in the headwind? Bottom line is watts are watts.
  • GMAN 19030GMAN 19030
    You're going to want to change gears to keep the same cadence.
  • rmillerrmiller

    Here's the explanation from a physics standpoint: Power (watts) are the product of torque and angular velocity. You're sensing of pedal pressure is related to the torque - so if your pedal pressure is similar (ie, you are applying the same amount of torque), but your velocity decreases, your overall power will decrease. You'll have to increase cadence to compensate and generate the same amount of power you were before.



    My guess - probably all in your head. image

    I know I'd mentally compensate when going up hill by thinking that I"m working against gravity. It's a lot more difficult to realize the excess drag created by a headwind.



  • mcstrangelovemcstrangelove

    Yeah, I try to keep the same cadence 85-95 rpm no matter what.  A change of a few watts is one thing, but mine just plummet when there's a strong headwind.

  • Al TruscottAl Truscott

     I think another thing which happens in winds ... Head, side, etc ... Is we spend extra energy with all body parts, including legs, making micro adjustments attempting to remain stable. So the effort which would normally go more directly to the pedals is spent trying to remain stable and upright. So the same effort produces less watts on the cranks or hub?

  • benvanmarckebenvanmarcke
    I can not imagine this being a mechanical thing. The powertap works through strain gauges, they measure the elastic deformation on the hub, convert it to torque and, after multiplying with velocity, to power. Thing is though, those gauges don't know and don't care whether the deformation is caused by wind, uphill, an attack to beat the buddies for a town line, etc. Deformation is deformation, and the amount gets converted to power regardless of its origin.

    So, in my opinion, there is absolutely nothing wrong with your powertap, probably your perception of power is 'miscalibrated' so to speak during stronger headwinds. (Personally I also find my perception to be miscalibrated i.e. I tend to push too hard on short, steep hills and not hard enough during head winds).
  • Joe MatchetteJoe Matchette
    Mac - I have very similar feelings as I discussed during some of last year's Race Rehearsals. I don't have anything definitive to add, but I think it is a combination of what Al says (micro-adjustments of all supporting muscles) as well as a psychological component --- similart to trying to keep watts up on a slight downhill. When I am trying to keep my watts "up" while going slightly "down", even with plenty of gears so that my cadence is in my Normal Zone, my RPE feels a couple of points higher than the flats. The converse is true when going uphill. It is very easy to overshoot my desired watts becuase it feels 'easier' to fight gravity than wind.

    So, long story short -- the watts are still the same, it is just the RPE that varies. So, yes, it IS all in our heads.
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