Power Differences

Discussion in 'Power Training' started by factory61, Jul 9, 2007.

  1. factory61

    factory61 New Member

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    I just went on a 3 hour ride with a friend of mine, and my average wattage was 20 watts higher than his for the same ride. During the climbs, we were pretty close, but overall it seems he had a much easier day than me. I am new to the sport and would like to better understand how this may have happened.

    Here are a few details that may help, and combined I'm assuming may account for the difference:

    1) He is 6lbs lighter than I am
    2) He is riding a tri bike and I'm on a road bike
    3) His avg cadence when pedalling is around 98, mine is around 92
    4) His tires hold 20lbs more pressure than mine (rolling resistance?)

    Appreciate your thoughts-
     
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  2. Bikeridindude

    Bikeridindude New Member

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    Those things combined make up for a large difference in cadence. A 6 pound difference going up hills would be significant enough for you to notice, a lot of the technical guys on here will tell you exactly how much. His being on a tri bike would put him in more of an aerodynamic position, therefore requiring less power to keep him going the same speed as you. The cadence wouldn't make any difference at all. Tire pressure may or may not, just because it has a higher pressure doesn't necessarily mean that his have a lower rolling resistance, but it's possible. Also, did you draft off of each other? That has the biggest impact of all (30%) on the flats. Who spent the most time on the front? If you are new, it sounds like you had a very good experiment as to the importance of the ratio of power/weight and the impact of drafting. It took me awhile to believe that drafting actually helped that much when I first started. All I had was a HRM. But one day a friend and I went on a ride into a strong headwind and my workout download showed it all before my very eyes. Our speed stayed constant throughout, but when I was on the front my HR was about 30 bpm higher than when he was on the front. It's pretty interesting stuff, enjoy learning all about it!
     
  3. factory61

    factory61 New Member

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    I guess I left out a couple of things that could be helpful. I actually drafted off him more that he did me. We are both using PT meters (should be closer results than if they were diff meters). We both zeroed out the torque befor the ride.

    I do have a fairly upright position on the bike since I am used to riding MTB instead. I may have to re-evaluate my position on the bike.
     
  4. Nicolai Foss

    Nicolai Foss New Member

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    just having different quality tires could explain a lot of the difference, the rest is weight and aerodynamics.
     
  5. daveryanwyoming

    daveryanwyoming Well-Known Member

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    There are a couple of additional factors that could give you a 20 watt difference in average power.

    - Do you both have your PT computers set to record zeros for power collection? If he records zeros for power averaging and you do not and you coasted a bit here and there you could easily see a 20 watt difference.

    - Have both PT hubs been torque tested and how do they compare? I have a few PT hubs and static torque tests show about a 4% spread in accuracy from the highest to lowest reading hub. At 250 watts AP that's a 10 watt difference.

    -Did you examine the rides in WKO+ side by side to see that you're comparing the same segments or did he spin around a bit waiting for you at any point? Unless it's the same effort for the same distance at the same speed (preferably you started and stopped your intervals at nearly the same time and that's what you're comparing) then all bets are off. A few minutes of zero data at one end of the ride or the other could easily pull his average down by 20 watts.

    -Dave
     
  6. factory61

    factory61 New Member

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    Good info!

    Settings are the same and we started and stopped the ride at the same time and rode together the entire ride.

    I have not had my hub torque tested and I don't know if he has either. Is that easy to do? How would I get that done?
     
  7. daveryanwyoming

    daveryanwyoming Well-Known Member

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    Check out: http://www.midweekclub.ca/powerFAQ.htm#Q23

    It's best to use fixed weights instead of bodyweight especially to make side by side comparisons between PTs, but either way will give you a good accuracy estimate.

    -Dave
     
  8. peterpen

    peterpen New Member

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    That 20w difference could *easily* be caused by his better aerodynamics, lower weight, and the fact that you drafted off him more than vice versa.

    If you can zero the torque on your PT, and don't regularly have problems with it drifting, I wouldn't worry about doing the "stomp test."
     
  9. Ergoman

    Ergoman New Member

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    There are so many factors at play here (as noted in previous answers) that it's actually amazing that you only had a 20 watt difference.

    Different bikes, different aerodynamic positions
    Different wheels and tires
    Different weights in the climbs
    Different power meters (in independent tests, PT accuracy -2 to +2.9%)
    Different drafting

    Be happy and work on increasing YOUR power and YOUR efficiency.
     
  10. grahamspringett

    grahamspringett New Member

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    Spot on. An excellent answer. We're all different, we all weigh different amounts, so we all put out different power. Besides, a 20W difference is hardly a great amount.
     
  11. factory61

    factory61 New Member

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    I appreciate everyones input. At first I was a little concerned that I should think about changing the way that I ride. After reading all of these posts, I think I'll just focus on putting in the work and let the rest fall where it may.


    Thanks to everyone-
     
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