sch340 wrote:
bgoldstein wrote:
jsaunders wrote:
To answer your question, you could run TR using virtual power and if you have a bike computer you could record the 20min test using that for actual power and then compare the two.
This. But make sure you multiply [20min segment power] * 0.95 so it will match the new TR estimate for FTP. Or you could just look at the ratio of average power from PM to average virtual power over that period and adjust accordingly.
It looks like my Power2Max is stuck in Customs limbo somewhere so I may have to go ahead and do my 20 minute test with only virtual power again for now given time constraints.
However, I can probably just estimate my real FTP by spinning for ~10 minutes with both the PM (connected to the bike computer) and virtual power with TR, correct?
So for example say I re-test at 300 W for virtual power on Wednesday. Next week I hook up the PM and spin for 10 min at an average of 200 virtual watts over that period, and my PM output reads an average of 180 over the same period for a ratio of 0.9 virtual/real. That means I could rightly assume my real FTP is 270.. or does it not scale linearly (in which case I could do an interval at or near FTP).
I believe the best answer is "it depends." While I would have agreed with RONDAL prior to attempting this myself, I'm skeptical based on my experiences after installing a Quarq. The dependability of the virtual estimate, however, is determined by your trainer and not by your PM.
I use a Cycleops Fluid2 and despite reading about all of the inconsistencies with the power curve, I didn't really believe my unit was affected when I was using virtual power. As soon as I installed the Quarq I could tell something was wrong, and the variability between the two numbers was neither neither consistent nor linear. It is my understanding, based on numerous threads (this one included, I believe), that the Kurt Kinetic fluid trainers will provide a much more dependable virtual power estimate.
So I'd say, give it a shot. If you want, you can look up or ask about experiences with virtual power as it relates to your specific trainer. You should be able to tell rather quickly if the numbers are lining up correctly. To get the best estimate, I'd look at a few 10-minute segments within the same ride to asses the variability as the trainer warms up. If those are somewhat consistent, you can probably use the numbers. If not, you should be able to ballpark your "true" FTP, but it might need to be tuned with an "official" FTP test using the new PM.