A guesstimate on a guesstimate isn’t going to be great in terms of accuracy. Though as the 20 minute test is 95% and the 8 minute test 90% one could argue that perhaps 92.5% would make somewhat sense? Though that’s completely ignoring all physiological aspects.
Did you do 5 minutes above threshold before the effort?
Do the 20. Not 1 second less. Stop with all the shorting. You’re not doing yourself any favors. If you’re worried about a low number just remember it’s a number. True performance in events and metrics like speed and climbing ability are what matter. No one cares what your ftp is.
FWIW I did a 16 minute test (395W) without the 5 minute effort, right before my last block. I ended up setting FTP at 365 (92.5%), and the workouts felt just about right (370 was too hard) throughout the whole block.
Yes, but with limitations. Firstly, once you are well trained and have completed a good number of tests you get a sense for your FTP from a range of efforts. Problem for a lot of people is that they don’t ever do long sustained efforts (approx 1hr) so they don’t really get a feel for it.
Secondly, there is a issue around completing the efforts on a hill. If the hill is steep and you are getting out of the saddle regularly your power output may be different to what it would be in the saddle. Also if the hill is not a smooth gradient, you may have bursts of power that skew your data.
The third issue is around repeating them as intervals. The rest between the intervals, the number and the consistency would skew the data. For example, there is a big difference between six 15 minute intervals with a 2 minute rest, than three intervals with a 10 minute break in between.
Everyone is different, so would respond differently to the protocol you have used relative to their FTP. You can only find out when you start undertaking training using the numbers.
Final point, if you don’t do a consistent repeatable protocol, it is hard for you to determine to what extent our training is having an impact.
So in summary, it would give you a number somewhere in ball park, but there are better options
The op asked specifically about 20 minutes, however, the same could be said of any test. I think pacing for 5 to 10 minutes is insanely more difficult than 20-40 etc…IMO, taking an estimate (algorithm of PDCs?) of an estimate (.95 of 20 min) used as a proxy for maximum lactate steady state, seems to me, like the whole point of testing is getting lost.
I guess I’m in the minority or a bit old school. I want a number to work zones to push the PDC up and right to compete. Getting familiar with riding longer maximum efforts are essential to this. Also, since my ftp seems to fluctuate 40w in a season doing the same test the same way seems critical.
Sorry another plug for my s/w but Intervals.icu helps with pacing issues. If you go out to hard go as long as you can and if its only 18 mins you will still get an FTP number. If you get to 20m and have gas in the tank keep at it and you will get a higher number for every bit over 20m at that power.