Ai_1 wrote:
I'm not that familiar with the Kickr, but everything you describe is easily explained by the subjective nature of effort perception, and without some other means of ruling this out, I don't think I'd be suspecting a decent smart trainer of huge inaccuracy. If you have a friend with a trainer, start riding on that and then switch to your one mid ride. See if it still gets easier 5 mins after switching. When you turn on the fan, try shielding the trainer from the airflow and see if the ride still seems to get easier. I suspect both of these tests are likely to demonstrate that your perception, not the trainer's accuracy, is whats changing...
Maintaining decent power always feels harder when you're not warmed up and "in the zone". Hard efforts also feel much harder if you're overheating. It's pretty much impossible to maintain adequate cooling indoors at anything more than super easy pedalling without a significant forced airflow. So a fan will always make it easier because it almost instantly reduces overheating that suppresses performance.
I run Assioma pedals with a Kickr gen 1. I have 2 sets of Assioma Unos in fact, on 2 separate bikes, and their power numbers line up pretty much exactly across a range of similar efforts, so I trust that they are accurate.
In summer/warm weather where my garage is over 65F, my Kickr power is really, really close to the Assioma readings (I measure the Assioma on my Garmin 945 but run the Kickr/Zwift off its internal powermeter and let that data be stored separately for 2 different power measurements per ride.)
When it's cold in my garage though, esp <55F in the dead of winter (Norcal) the Kickr gen 1 definitely starts off with a power discrepancy compared to my Assiomas (which have built in temperature adjustment), as much a 20 watts 'easier' at the start of a ride, and after I warm up the machine for a good 30+ minutes or more depending on effort, the gap closes until it's pretty much gone.
Long story short, the Kickr gen 1 at least definitely does have a 'warmup to accurate power' from cold starts in cold rooms which would definitely account for what OP is feeling, from an objective basis. I see it directly on my Garmin/Assioma power vs the Kickr/Zwift displayed power in realtime.
I know I could let the Kickr be controlled by the Assioma and have this whole discrepancy be done with, but I find the power readings in realtime fluctuate a lot more when I do this, to the point that erg mode feels almost unusable as it's so jumpy as a result. As well, I have a long history of Zwift rides controlled by the Kickr which are really reproducible (down to the 0.1 watt for race efforts!) so it screws things up to switch over to a new power system. I do only rely on the Assioma readings for planning future outdoor races or outdoor training power efforts, not the Kickr ones as a result.