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Dailing in bike fit with power meter

robert boisvertrobert boisvert
in General Training Discussions

Hi,

Just got my Power meter !    Id like to dial in my bike fit  ( i have a bad habit of tweaking it).    Anyone have any  simple tests that could be performed on a trainer?  Ive heard of "Constant Speed Test"  and the "Constant HR" test.   It seems the most logical way would be to run constant watts and see how far I go, but i noticed watts jump 15-20 and im not sure if this would be the best way to get an accurate read.

 

Rob

 

Comments

  • GMAN 19030GMAN 19030

    I'd really caution against dialing in your bike fit based off power.  One position might be more powerful than another but there's always a trade off.  Usually it's comfort but it could also be aerodynamics.  A more powerful postion doesn't necessarily translate to a faster race.



    I can get more power with a more aggressive position but it doesn't mean much since I can't ride very long in that position, let alone being able to effectively run after spending xx time in that position. It's a balance of comfort vs power. Maybe you can get away with a real aggressive and powerful position in a sprint but you'd need a chiropractor and a urologist after attempting to ride that position for 56 or 112 miles.

    I'd suggest you train with the power meter for awhile.  Read some books like the Coggan & Allen book and browse all that EN offers through the Wiki and the Power Webinar.   Get a good dialed in professional fitting and then maybe do some slight tweaking somewhere down the road.

  • robert boisvertrobert boisvert
    Gotcha....makes sense.

    Thank you
  • William JenksWilliam Jenks
    I think the first thing people who get a power meter should do is just "play" for 2-4 weeks. Watch your power during the ride. Download your data and see what the actual Ave Power and NP are for the ride... Find out what it feels like to go XXX power for 1 minute, 5 minutes, etc. As you get more comfortable with it and self-knowledgable, set yourself up for a good FTP test at the end of that time. (I'm assuming you aren't racing any time in the next few weeks.)

    Bob is 100% right about the trade-offs. I probably went a bit far this year in the direction of sacrificing power for speed, in that my FTP went down more than it should have comparing my sit-up winter power to my TT bike power...but my speed was at least as good as last year overall and I was definitely faster per watt. But I'm working now on a solution to moderate the drop off, hopefully minimizing any negative effects.
  • mgraffeomgraffeo
    There are protocols online (google Chung bike power protocol) to help you measure your aerodynamic drag with a loop course you can repeat, and a power meter. It seems to work, though it's a bit complex (spreadsheet you need to download, helps to have a loop with very few cars, no change in air temps/humidity, etc). I will probably be doing something like this next spring.

    An alternative is to buy an IBike aero head unit to go along with a wireless PowerTap or other PM. With that combo, you would have real-time CdA measurements, so you would see the impact of changes right away. More expensive than a Joule, less expensive than a wind tunnel...
  • cwhytecwhyte
    Also never forget that all position changes require some adaptation time. For example, there's a good chance that you'll see a drop in power as you lower your position but there's a very good chance that power will return after riding in that position for a couple of weeks.
  • Chris GChris G
    tweaking your bike fit is usually a bad idea. Once it is right it should not be changed. A good fit should not come with any power trade offs once you have adapted to it as Chris suggests. Most of the time people get a fitting done and then make it worse by tweaking. It should only change if your body changes pretty drastically. Assuming that you are not still growing that only leaves large amounts of weight gain or loss.
  • kjanracingkjanracing
    There is also the mental part of thinking a certain position may be faster so you pedal a little harder. I've tried to "fit by power" on my computrainer, but it was inconclusive for me. Let your power adapt to a good fit.
  • GMAN 19030GMAN 19030
    Posted By Kurt Andersen on 26 Sep 2011 01:33 PM
    Let your power adapt to a good fit.



    Pretty much spot on.

  • Coach RichCoach Rich

    All good points. You fit for increased speed at a given acceptable comfort level. That comfort level is a function of race distance, ie, what level of comfort do you need/want/prefer for a bike ride of x length. Power just shakes itself out.

    That is, I can have a very non-aero fit and be very comfortable and powerful...but slower than a more aero, but still comfortable-enough fit at a lesser power. There's also a tendency to chase a higher power number during a fitting session, especially if you are paying for said session

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