A few simple Time Trial questions

Discussion in 'Power Training' started by koger, Jun 14, 2008.

  1. koger

    koger New Member

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    Hello

    I have done my second Time Trial with a power meter, and have little experience. So I thought why not ask the clever people here :)

    I did a 30km out and home route, mostly flat, but with a few short hills.

    My plan was to try to keep the power fixed at 340w, I did that pretty well. But am now thinking if should have aimed for 345w.
    The first half was almost easy, while the last quarter of the race was pretty hard, is that normal? How do you experience the pain during a time trial, and how do you adjust?

    Racing with a aero disc wheel instead of a normal wheel, how much time do you think that would have earned me on a 30km route?

    Thanks for any advice :)
     
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  2. daveryanwyoming

    daveryanwyoming Well-Known Member

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    Yes, if you've paced it fairly well the first part shouldn't feel brutal but the end is always tough. If you pace poorly and go out too hard the first part will feel harder and the finish will be absolutely brutal or easy if you totally blow and give up (but very slow).
    I don't really understand your question. I experience discomfort, legs getting heavy, deep possibly ragged breathing, etc. It depends in part on whether it's a short or long TT, in the short efforts my power is higher and my breathing is really uncomfortable by the half way point, in a 40K my breathing is steadier but my legs get heavy and concentration becomes difficult for me about 40 minutes into the effort.

    Adjusting just means better concentration, better pacing each time I do a TT. More focus on starting quickly without digging a huge hole that I can't climb out of, using my gears effectively, etc. A TT will always hurt, if not you could have gone faster. With good power pacing it hurts less by learning not to start too fast but in the end it's still a big effort. No easy answers here, ride more of them and pay attention to pacing, gearing, mental focus and you'll improve. Was this an actual TT in competiion or a training TT? That wasn't clear from your post, but I can't push myself nearly as hard during training TTs as I can with a number on my back, folks to chase and folks to stay away from. Nothing like competition to bring out that extra effort.

    That's tough to say, but probably not as much as you think. Body aerodynamics come first so a good position that still allows you to generate power is key. Helmets and wheels come after that, an aero helmet and good aero wheels can help a lot but won't do much if you don't have a good aero position. Accessories like shoe covers and skinsuits help as well, but again start by finding your most aero position that still allows you to generate power and is comfortable enough to stay in for the entire race and still allows you to see up the road. Start with that and add wheels, helmets and other accessories to go faster.

    There are some published studies that claim certain savings in watts for different wheels, forks, helmets, etc. But aerodynamics isn't a matter of the sum of the parts. Your CdA can't be calculated by adding up the drag coefficients of different components particularly if you ignore the most important part, your body position. The good news is you can use several methods like RChung's lap based method or speed vs. power regressions to estimate your CdA with different positions and with different equipment combos.

    Good luck,
    -Dave
     
  3. Tapeworm

    Tapeworm New Member

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    A TT should be done so you are just about passing out when you cross the finish line. Sustained continuous effort is usually the way to go. Circumstances may require a different approach ie: a hilly course (which would mean higher power output going up, less going down, but not too much less!).

    Pain, well that goes with TTing. But it depend what you mean by pain. Breathing really hard, heart hammering and legs burning, losing vision etc, should be the sensation at the end. If it's at the start you may have gone out too hard...

    Any other pain, sore back, sore knee etc may indicate incorrect position or maybe something else. If you plan on doing more TTs you should train in the TT position.

    Aero savings diminish as speed goes up. A disc WILL make you go faster though by how much is hard to say. Over a 30km course depending on wind direction and your speed you could save up to 30sec - totally a ballpark figure. Lots of testing would need to be done to verify exactly how much. And people may try to tell you that a disk is not a good idea in strong crosswinds. To that I say "bollocks". I've never had a problem and it gets fairly windy here.

    My 2 cents worth...
     
  4. Terry Ferguson

    Terry Ferguson New Member

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    "Aero savings diminish as speed goes up." ??? - TF
     
  5. rmur17

    rmur17 New Member

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    yes in an absolute sense on typical TT courses that is correct. Faster riders just spend less time on the course ...

    Now if you consider a mountain TT vs. flat , that's another matter!
     
  6. Piotr

    Piotr New Member

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    I that sense, all time savings dimish as time to completion dimishes, but to imply that improved aerodynamics are less helpful at higher speeds is incorrect.
     
  7. rmur17

    rmur17 New Member

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    I stand by my comment on the statement above but I can't control how anyone may care to spin it ... it's simple high-school physics ...
     
  8. Alex Simmons

    Alex Simmons Member

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    You're kind of both right.

    An example to illustrate:

    Two riders over same course and conditions (say a dead flat and windless 16km TT) with the exact same biomechanical profile: CdA (0.3m^2), Crr (0.005) and total mass (90kg). Taking a 20C, 1020hPa, 65% humidity day:

    Then if Rider A can generate 400W for the TT and Rider B 240W:

    Rider A takes 20:19 to cover 16km (13.13 m/s)
    Rider B takes 24:37 (10.83 m/s)

    Reduce both riders CdA by 10% to 0.27

    Rider A drops time by just under 40 seconds (13.57 m/s = +3.3% in speed)
    Rider B drops time by just under 47 seconds (11.19 m/s = +3.3% in speed)

    So while both riders essentially get a similar % improvement in speed, rider B get a larger absolute time saving.
     
  9. Tapeworm

    Tapeworm New Member

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    Sorry, my bad, should have been more specific with my posting. I was not trying to imply for a second that aerodynamics are not important at higher speeds, just the amount of time saved reduces as the speed increases.

    This in turn makes the art of being aero more crucial. The differences in time become less and thus every second becomes more important.

    Now just to muddy the waters a bit more I also thought that one reason that the aero benefit diminishes as speed increases is that the "savings" in wattage do not translate to an equal increase of speed due to the non linear nature of drag (being quadratic)? ie: you are "saving" less than you are spending? Have I got this wrong?
     
  10. Alex Simmons

    Alex Simmons Member

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    You'll note the 10% reduction in air resistance has only resulted in a little over 3% increase in speed. That is the quadratic component in action.
     
  11. TheDarkLord

    TheDarkLord New Member

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    Actually, that would be consistent with a cubic rather than quadratic component. For a quadratic term, you should see a 5% rather than 3% increase in speed.
     
  12. Alex Simmons

    Alex Simmons Member

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    true
    how could I forget the fun of working out how to get excel to solve the cubic equations of motion for a cyclist :)
     
  13. rmur17

    rmur17 New Member

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    that's why I specified absolute rather than relative :p .

    Are you still looking for some TT data BTW? I have all kinds of summary data on my work computer here but the raw data (SRM,wko) is at home and I keep forgetting to email some in here ..
     
  14. koger

    koger New Member

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    Hi again

    Thanks for your answers :)

    When I'm reading yours and others posts, I'm starting to think that perhaps I wasn't doing the best I could. The hard part seems to determine how hard I really can go, I guess you only know when crossing the limit. As you say, competition really should enable me to hold a few more watts than I would during training.

    I think that leads to two other questions. Do you start out at your estimated training FTP? slightly below to avoid exploding or slightly more, because you think about extra kick the competion will give you should.

    And another question, how do you motivate yourself during a TT when it really starts to get tough?

     
  15. daveryanwyoming

    daveryanwyoming Well-Known Member

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    Every TT I've ever done I've planned to start a few watts below FTP and ramp into it.....it hasn't played out that way yet. The first few seconds will always be well above FTP as you're doing a standing start, even if you take it pretty easy (and I've definitely learned to moderate my start to avoid a huge power spike at the start) it's normal to hit two or three times my FTP for a few seconds. From there it's hard to mellow to a pace below FTP without totally coasting so I tend to settle down over the first minute or two to something near FTP and then try to stabilize there.

    That's a huge question and depends in part on how you are motivated as a person. I review my power data after each race and that's how I keyed in on overly fast starts and my fade around the 40 minute mark. Now I work hard on extra focus as I approach that point and I've steadied out a bit in my last few TTs. Check out some good sports psychology books if you need tips on motivation and focus during athletic events. I don't claim to know enough to give advice in that arena. The only tip I can give is to be fired up, psyched to race, confident from your training that you'll at least be competitive and give it your best start to finish.

    Keep doing them and you'll figure out what works for you. It's an ongoing process and I'm certain I haven't yet achieved my best results.

    Good luck,
    -Dave
     
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