New to power. Questions

Discussion in 'Power Training' started by bigbevans, Dec 13, 2005.

  1. bigbevans

    bigbevans New Member

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    Does the Powertap SL come with a magnet for the cadence sensor? I have just got one and have a cadence sensor but no magnet for the crank!

    Additionally I am trying to work out what sort of 25 mile(40k) power I needed to do a 55min. Just a rough figure, I am 5' 6" (167cm).
     
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  2. frenchyge

    frenchyge New Member

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    Yes, there should be one.

    Wow, that's really aero dependent. For just the frontal area figure, using .4 m^2 or .5 m^2 gives a difference in power between 264w and 321w for the hour based on the tools at www.analyticcycling.com.

    If you really wanted to jump right into the FT test, my recommendation would be to start the test at ~250w and slowly increase until you reach the 1hr TT intensity you are used to. I think just riding around with it a little to get a feel for the different power levels (as Rapdaddyo suggested) would be a better approach, however.
     
  3. bigbevans

    bigbevans New Member

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    OK thanks.

    I am trying to work out how my fitness compares now to the height of the season. I guess this will be something I will know this time next year, once I have collected enough data. :)

    I'll have to have a bit more of a look in the box for the magnet.
     
  4. frenchyge

    frenchyge New Member

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    My magnet was in the plastic bag with all the zip ties.

    It's not necessary to collect an entire year's worth of data to get a decent feel -- a couple rides will suffice. In fact, after 20 minutes on the bike, it'll be obvious whether 260w or 320w is closer to the value you could hold for an hour.;)
     
  5. RapDaddyo

    RapDaddyo Active Member

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    When you find your magnet, you'll get a clean installation by using Blue RTV Silicone. You can get this stuff at an auto parts store. No ties.

    You'll be able to figure this out fairly quickly. Find a flat road section (easier said than done -- nobody ever told the highway engineers that we cyclists need some flat road sections for testing) ~1 mile in length on a day with light crosswinds (e.g., 5mph). Ride your TT bike setup and position and get up to your target speed (e.g., 27mph). Start your interval marker at the beginning and end of the run. Actually, I often terminate my intervals by going to a zero cadence for ~15 secs. It's easy to find the end of the interval when you look at the workout file by displaying cadence and just looking for where it drops to zero. Maintain the speed for ~3 minutes and look at the avg power when you download the workout file. Now, don't get too enamored with the power number you get. No TTs are run on flat courses with no wind. So, you'll need to bump the number you get by various factors based on the specific course (hills and wind).

    BTW, FWIW I found that one of the challenges of riding with power is trying to ride at a specific power level. It's easy to fall into the trap of what I call "watts hunting," constantly over- and under-shooting the target power. After some experimentation, I settled on riding at a constant cadence once I got up to about the right power. Then, until there is a major change in grade or wind, I micro-manage my power with cadence, with each RPM being equal to 1% of my target power.
     
  6. rmur17

    rmur17 New Member

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    I would at least repeat the test in the opposite direction and average the two to reduce the effect of road slope and deviation from 90 deg. wind direction. You'll likely be hard-pressed to find a perfectly calm day or a pure x-wind (or a perhaps a purely flat piece o'road).

    RD,
    Do you really ride that 'strictly'? Unless I've doing mid L4 work or above or TT'ng, I don't look at the PM much .. in fact my favorite habit is to simply set the PT display to Max Watts so my riding is not influenced by the meter.

    About the only time I check power on a long ride is at the mid-way water/pee stop or turnaround point so I can judge how much I have to (or am going to) hurt coming home :)

    YMMV,
    rmur
     
  7. RapDaddyo

    RapDaddyo Active Member

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    Good point. Of course, since it only defines the best-case scenario (flat, no wind) I wouldn't get too hung up on trying to narrow this test down to 2-3 watts.

    Yes, I do, but I should explain. I'm on a mission to define and ride optimal power management strategies on actual courses under actual conditions (e.g., wind). The optimal power management strategy exploits the physics involved, which favors riding at higher power when the bike is slow due to grade or wind, under the constraint of a target NP for the entire ride (FT for rides ~1 hr), which favors riding at constant power due to the penalty associated with the 4th power NP algorithm. So, my training goals are to increase my FT to my personal maximum potential and to learn to ride at precise and variable power levels. I ride every "hard" ride at precise, variable power levels. A typical ride has power levels ranging from ~100w to 600w, with a few max power 10-second efforts for neuromuscular adaptation.

    Currently available on-bike technology does not provide much support for what I am trying to do, so I'm venturing off the reservation to address that shortcoming. At first glance, such a power management strategy might appear to be applicable to ITTs, but I think it is also applicable to the late stages of mass-start races if one has enough power to contemplate trying to make a break. Fundamentally, I want to know in advance if it is likely that I will be able to sustain a break given an estimate of my NP for the remainder of the course (which is of course a function of my cumulative NP to that point and the remaining duration of the course) vs. what I think a chase group can sustain. I think it requires a differential of at least 50w to sustain a break if the group is organized. I do not want to go by "feel," I want to make an objective decision based on facts.
     
  8. bigbevans

    bigbevans New Member

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    It would help me if you could give your 40k performance on watts and time to give me some ideas. :cool:
     
  9. RapDaddyo

    RapDaddyo Active Member

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    Not sure who your question is directed to. Times are going to be all over the map, based on the course and wind conditions, the bike and wheels, one's sustainable power and how close to optimal one is able to manage power on the ride. My most recent full hour NP was 316w. I hardly ever ride at a constant power for longer than a few minutes, so I rely on NP to estimate my FT.
     
  10. MikeHains

    MikeHains New Member

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    frenchyge's is right. Somewhere between 264w and 321w is right ... as long as you are riding aero.

    If brilliantly aero - then 264w might be achievable. If you ride a road bike with hands on the hoods - then you probably won't even do it at 321w.

    But you want a rough guide ... so: at 5'10", 74kg, on a road bike, but with aero bars, and Zipp 808 wheels, on level ground, with no wind, 276w = 40.1 kph for me.

    Hope that helps, regards, MJH
     
  11. bigbevans

    bigbevans New Member

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    Spot on it was in with the cable ties. I need new glasses :eek: Thanks
     
  12. bigbevans

    bigbevans New Member

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    I did my first 25 mile(40k) event today. Finished in 59:55 avg power 256 watts (NP 259 watts). So I reckon based on those figures a 55 min 25 would take about 320 watts for me.
     
  13. whoawhoa

    whoawhoa New Member

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    More like 340, I think.
     
  14. bigbevans

    bigbevans New Member

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    We'll I suppose we are just guestimating, and I'll just have to wait and see.
     
  15. whoawhoa

    whoawhoa New Member

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    It was a quick run through, but I used analyticcycling.com. Calculate for yourself, if you like.
     
  16. bigbevans

    bigbevans New Member

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    Yeah I fiddled about with that and http://www.kreuzotter.de/english/eindex.htm to come up with 320.
     
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