Originally Posted by
profjmb
I have always thought that given wind, weight, etc., power determines speed. But I was fooling around in a group ride today and noticed that going a steady speed (behind some guy), shifting between gears altered the power (and yes I did let the power meter settle down). I believe it was the case that easier gears (and thus higher cadence) led to higher power. Again, that's maintaining the same speed.
Physics nerds, what gives?
And if I'm right (and I saw it with my own eyes), is it possible to overvalue power?
That's not exactly a controlled environment for a test. Firstly you don't know if the rider in front of you was putting out constant power. Secondly power reported by a meter is quite stochastic so you'd need to carefully average over a reasonable period of time to get meaningful numbers to do a comparison.
There can be small changes in drivetrain efficiency between different gears which might be measureable with a crank-based powermeter but as I said above the conditions for your test are too variable to measure the small differences that exist.
Suspect you were just seeing coincidental changes in power.