Can of worms here for sure.R314 wrote: ↑Thu Dec 09, 2021 2:52 pmMaybe it is just me, but there is one thing i can't get my head around.
I expect the further you go from the pedal axle the more power is lost. Crank has some degreree of flex, the derivetrain also has some losses etc.
It seems like people are so fixated on having the same number at all point of measurement, yet none of these PMs are validated by a 3rd party just manufatrurers claims. I noticed people tend to belive the device reports the highest value is the most accurate.
I see a few posts above showing the NEO. I used the Elite DiretoXR in my most recent AXO test. (and the Wahoo Kickr 5 in other recent testing). I've been told by one of the big players they do factor in a small amount of mechanical loss to their power calcs. They're all pretty secretive about exactly what they're doing with power measurement. Mechanical losses aren't consistent either so it's not as easy as a 1.5% upscale, although I suspect that's ballpark to what is being applied by some.
I do my best to remove the biggest factors that influence drivetrain loss. My ERG testing is using a straight chainline. The drivetrain is immaculately clean. I use a quality BB and jockey wheel bearings. I even upgraded to a CeramicSpeed OSPW on one bike... but observed no change in power numbers. The testing protocol is also important.
I'm of the opinion (and I know a lot of people disagree) that power measurement should relate to the energy expenditure of the rider. "What am I doing" as opposed to "What am I doing +- the measurement point". Having power reported only from the measurement point means if you have multiple meters measuring at different points you'll have a different FTP (4DP too I guess), a different experience with these new online platforms, and your training data will be messy, if you really care about the finer details. There's no standard on this though, so it's likely people will argue both ways.
I see drivetrain loss thrown around way too much when it comes to people questioning power comparisons. It's a beautiful excuse for companies to use too quickly close support tickets. Resolving power discrepancies is a pain in the arse. Made harder when companies make up excuses as to why their power meter is junky. I'm sent a lot of communication from users and their interactions with power meter companies.
"these devices don't measure power directly as bike ones do, but rather estimate it, and therefore CANNOT be used to compare with bike ones." - A power meter company response to someone asking why their meter is well off from their smart trainer. This is complete and utter bullshit.
There's a LOT more companies could be doing when it comes to defining what they consider 'accuracy' to be. Put any smart trainer in the 53/11 at 200W ERG and watch the 'accuracy' go flying out the window.
Anyhow... tldr; I'll happily give up a few watts to 'drivetrain'. Not as many as what I see thrown around though.
