FTP calculation questions.

ben@31
ben@31 Posts: 2,327
Im new to powermeters and wanting to calculate my FTP. Ive read it needs to be 20 minutes max effort and Im now trying to find a quiet road thats long enough.

1) As long as I keep the effort up does the gradient make much difference? As one possible road starts to descend after several km by -1 to -2% ?

2) If I can turn around without stopping can you accurately calculate FTP by doing a "there and back" on the same stretch of road ?

3) Another road passes through a village with a poor road surface and a speed bump, if I ease off the effort for a few seconds will this alter the accuracy by much ?

4) More importantly how do you keep at 100% effort and not 95% or 90% ? I find I naturally slow down into my comfort zone and can always push harder.

Thanks.
"The Prince of Wales is now the King of France" - Calton Kirby

Comments

  • sungod
    sungod Posts: 16,736
    the 20 minute test is only an estimate

    far more important than ftp accuracy is consistency, you need to be able to repeat the test periodically to check what progress you are making, choose a test protocol and route that will enable this, stick to it

    personally i prefer to test on a turbo or wattbike, but if you will do it on the road choose the safest route, if there're traffic/other hazards it'll be harder to keep focussed and stay safe

    i wouldn't worry too much about momentary changes in effort, as long as your gearing allows taking the gradients without crazy cadence changes (efficiency varies with cadence) and you do any turn/whatever fast enough that you don't get any recovery time, just remember to keep it consistent each time you repeat

    your objective is to do 20 minutes at 100% of the effort you can sustain for that time, look at the stats from the powermeter data for your best 20 minute power, assuming you haven't been really trying so far, do some test runs to see what power you should aim at for the test, then when you do the test keep to that power, not under, not over

    your performance can be constrained mentally as well as physically - if discomfort causes you to reduce effort, the ftp estimate is still valid, part of training is to learn to handle the discomfort/pain of high effort and keep cranking out the power
    my bike - faster than god's and twice as shiny
  • AK_jnr
    AK_jnr Posts: 717
    Mountains are the best, I've had my best 20 minute outputs on them but obviously thats not possible here.
    The best road I can find near me is an 8 minute climb but I can use the flat road leading in to it without interuptions to make it to 20 minutes. Not ideal if you have a tailwind as you will get to the top before the time is up but its repeatable which is the main thing.
  • amaferanga
    amaferanga Posts: 6,789
    Doesn't need to be 20 minutes.
    More problems but still living....
  • ben@31 wrote:
    Im new to powermeters and wanting to calculate my FTP. Ive read it needs to be 20 minutes max effort and Im now trying to find a quiet road thats long enough.

    1) As long as I keep the effort up does the gradient make much difference? As one possible road starts to descend after several km by -1 to -2% ?

    2) If I can turn around without stopping can you accurately calculate FTP by doing a "there and back" on the same stretch of road ?

    3) Another road passes through a village with a poor road surface and a speed bump, if I ease off the effort for a few seconds will this alter the accuracy by much ?

    4) More importantly how do you keep at 100% effort and not 95% or 90% ? I find I naturally slow down into my comfort zone and can always push harder.

    Thanks.
    1. negative gradients can be harder to keep the power up on, depends on how well you concentrate on keeping the effort going.

    2. yes, the short time not pedalling isn't a big deal and the brief break just enables you to go a bit harder when you are pedalling

    3. as above, not really

    4. Pacing is a skill you learn with practice. Don't expect your first attempt to be right on the money. I often suggest a course that one can ride for longer than 20-min (loop courses are good if you have one). Start out pretty conservatively for first 5-min, below what you think you can do, then gradually lift as you get deeper into the effort. If it's clear you can go a fair bit harder and your opening minutes were well down on power, then simply extend the duration of your effort so you get 20 or so minutes at the higher power.

    There are many ways to establish FTP. Taking a percentage of your mean maximal 20-min power is another, although I'd probably use that as part of another method, e.g. establishing your Critical Power*. If finding a suitable course is problematic, there are other ways of getting a good estimate. Nowadays there are some good analytics software models that can examine your rides for data and extract the mean maximal data automatically to provide an FTP estimate. Some models are better than others though.

    * If you can get a good 20-min effort in (or longer), it would also help to also do a mean maximal effort over say 4-6 minutes as well. Combining the data from two test efforts for ~4-6 minutes and another for ~25 minutes enables you to calculate your Critical Power, which will be a good estimate of FTP provided you include the longer test.
  • philbar72
    philbar72 Posts: 2,229
    amaferanga wrote:
    Doesn't need to be 20 minutes.
    this. I do 12 and 15 minute sessions as well as the ubiquitous 3 x8 to work out where I am.