I’ve been using a power meter pedal for outdoor rides (recorded in Golden Cheetah) and SYSTM with a Kickr trainer once outdoor riding is finished for the past three seasons and am now accustomed to the following drill. Coming in from outside, the 4DP test will drop my FTP by 10 - 20%. A winter season of training will bring the number up by about 5%. Once the outdoor season starts again, FTP determined outside will be up by about 10% from the last 4DP. The reasons for this are well-discussed on the forum and I’m good with that, got the T-shirt.
But here’s another interesting observation. True to form, my 4DP test a couple of weeks ago dropped the FTP. After a couple of days rest, I decided to try out RGT for the first time by doing the Cap Formentor ride, a solid climb by any measure. At the beginning, I had entered the FTP value from the 4DP test into the RGT metrics. However, when I finished the ride, RGT suggested that my FTP had increased by 11%. So what gives? The explanations for indoor/outdoor differences don’t apply, since everything was done on the trainer.
That’s a bit of a mystery, as this was the first RGT road that I tried.
When setting up the RGT account, one enters weight and an FTP value. I assume that weight is used with slope data to determine the appropriate resistance when riding a virtual road, and FTP is used to set resistances if one is doing one of the RGT workouts in erg mode.
The Cap Formentor ride is a simulation, so resistance should be determined by the slope and the weight that I entered. Once you hit the the climb, it’s a fairly steady grind to the first “col.” I’d assume that the RGT algorithm works something like Training Peaks; if it detects a steady effort of 20 minutes or more it will interpret it as an FTP effort.
I have assumed, from what is in the knowledge base and forum discussions, that a difference between FTP determined as 95% of a 20 minute outdoor effort and that determined by a 4DP test on a trainer is due to the inability to use actions like swaying the bike side-to-side on a trainer to compensate for less than perfect pedaling technique. But perhaps these two tests are to some extent measuring different things?
Yes, agreed the two tests are measuring different things, or rather, estimating using different protocols, even though attempting to estimate the same thing (FTP). Indoor/outdoor can be different for a variety of reasons including position and cooling, but if you get your fan setup dialed, they may not be that different at all. I can actually sometimes find higher numbers indoors esp. as intervals get longer because there’s no instance where i run out of runway on the road and/or need to pause pedaling for a second like often happens outdoors.
Rather, i think main reason (i) 95% of a fresh 20 minute vs. (ii) a 20 minute done a few minutes after a max effort 5 minute (4DP) are goign to return different FTP numbers is that they are two different methods for estimating FTP. The output should be close (and any differences you experience would be interesting to unpack and could be useful sources of data in their own right) but no reason to expect them to be identical.
I would agree with the above 95% of a fresh 20 min is going to return a higher value as compared to the FF test which is designed to remove (as best as possible) the anaerobic contribution if you have been basing your outside FTP on a similar effort when going outside I would consider revisiting the protocol used outside