This is purely anecdotal but could it be your cadence is low during the initial ramp up? I too find that it's harder to push (cad = 0 or less than 50) and then progressive gets easier once my cadence is up and also once the flywheel gathers some momentum.

I doubt that temperature effects are that severe. Possibly a couple of watts but I won't know since my area is always HOT HOT HOT.30c

Very simplified and generalised answer is yes. Much much less than the old wheel on trainers, but still yes. Checkout DC rainmaker for details. Some trainers do this less than others. Some recalbrate as you go.

But not huge amounts. So your feeling is more as you warm up as much as the trainer. The midway fan thing is 100% you. Logically that's the opposite for the trainer at the start where it's harder when colder.

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.

What gen is your kickr?

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.

Even the most current advanced spin down procedures I see listed that show up on Zwift for the direct drive units list a "3min warmup period".

I would assume that doing something like this both seats the belt and warms things up a hair closer to operating temp.

I would imagine a longer period each time is necessary with wheel-on units due to the nature of heat generated going into the tire. Also with wheel-on units they have you spin down every time due to probable fluctuations in tire pressure (unless you're super religious on that and have a slam bang track pump).

I now do a pretty solid warmup on my Core before a spin down and find it to work better than jumping on and doing one straight cold.

The physics or engineering of it getting easier as you ride is likely due to changes in drivetrain efficiency both in the bike and in the drivetrain of the smart trainer as it warms. I could imagine a warmer bike chain perhaps has an imperceptible improvement in efficiency. I also could imagine a warmer smart trainer belt is more flexible and supple than a room temp belt. That stuff might be worth a single watt, who knows.

I have a Kickr Core and I experience the same thing. I think room temp does affect it as the day it was coolest, the resistance was temporarily highest.
A side note, my recorded trainer mph always seems very low relative to watts/mph outside. Like 12-13 mph when outside it would be closer to 19-20 mph.
Would a spin down test more often solve this?

I did say I wasn't that familiar with the Kickr ;)
So, I stand corrected on the Kickr data most likely being trustworthy, however I still reckon subjective perception is likely a big culprit, even if the trainer is also in doubt, and especially so for the perceived change when the fan is turned on.

Speaking only for Kickr Gen 1, I was hoping that a 10 min or less warmup would solve my power gap, but it doesn't, at least if I'm not racing hard. If my garage is cold (50F), it takes a good 35-45 minutes to get near my Assioma power. Not sure why it takes so long, but it does.

I'm hoping the newer-gen trainers don't have this effect in cold garages - I KNOW for sure that there are plenty folks out here who own Neo2Ts and run them with Assioma power pedals, so I'm waiting for them to chime in about how it's working for them regarding the power gap on cold garage type situations.

I do suspect that a post-warmup spindown might reflect better power numbers, but I've done spindowns as long as 15 minutes of warming the Kickr up and it definitely didn't fix the problem. I don't want to be bothered doing spindowns any later than that! For sure though, it's not as simple an issue as doing a new spindown before I start - I was hoping that would be the case, but it makes no difference.

Your observations on RPE and the body warming up is very true also.

Indoors or out I find the more aerobic fitness I have as a ratio to my overall fitness level, the more warmup I need. The other day it took about 45min of tempo and Z2 to warmup for an outdoor TT on a route I wanted to create on Strava. The RPE during that warmup was just bollocks. Not great even for tempo. But once warm and I was about 2min into hammering the TT route, all systems were go.

As for the cold garage spin down folks, if you don't have a wheel-on you don't need to be doing a spin down every time. Do your spin down on the direct drive trainer in the cold garage at the very end of your workout when it is up to temp itself and the garage likely warmed up by yourself. Then leave that spin down alone until either the weather temperature changes a lot OR you move/relocate/reposition the trainer and bike.

I think some direct drive folks may over-do the spin down thing versus do it in a very consistent way.

My Core is indoors, so temp is always going to be 66 +/- a degree in winter.

If you have the Assiomas, then why do you care if the smart trainer is matching that? Can't you just use the assiomas as the power source?

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I explained it above -

If I run assiomas as the power source to drive the Kickr Gen1, erg mode is no longer smooth. It gets so jumpy that it's almost unusable for me. As well, even with the 3-sec power smoothing, the displayed power numbers in real time are also annoyingly jumpy compared to using the internal Kickr PM.

And secondly, I have a long history of Zwift with ALL my numbers using Kickr Gen1 PM. I'd rather not go through the hassle of restarting my race history, etc. with a new set of power numbers.

But yes, if you absolutely must have your Assioma power, you can def let it control the kickr. I find it easier just to record my Assioma with my Garmin and also have the Kickr send its PM to Zwift. Smoother erg rides, more stable reported power ( a lot more stable) in real time, and very reproducible in races down to the 0.1 watt!

I guess I'm not really sure what relevance having reproducible Zwift rides matters to anything, especially not down to 0.1watt, and I'm not really interested in erg mode. So there's that, but that's me, not you.

I really don't need a smart trainer at all, except to simulate gradient in Zwift, but I can also kinda fake that by just changing gears.

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The reproducibility matters a lot. I want to see how I'm doing over time and with different training. I like having data in both the Assioma as well as the Kickr.

I actually don't use erg mode much either. But the occasional time I do it it's very helpful. I just used it for the Zwift FTP 20' test last week, actually.

I do agree that the smart trainer is closer to a luxury than a necessity. Dumb trainer itself is all you really NEED for quality bike training. All the other stuff are extras that make it nicer, more fun. For me it's worth it - indoor training is tough enough on its own that I don't mind spending some extra money to get me excited to be doing it regularly, day in day out. But yeah, I did the dumb trainer+PM hub for 4 years before the Kickr, and was just as good on the bike as I am now. It's def way more fun with Zwift events though!

I said reproducible "Zwift" rides.

You already have your data in Trainingpeaks and/or garmin connect, right? and that has a consistent power source, like PT hub or Assiomas? There's your source for determining improvement. and 0.1 W really does not matter, since the accuracy of any of these devices is at least +/- 1%

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I got my Assioma less than a year ago. My zwift ride history goes on well before that, at least I have a LOT of non-Assioma rides predating getting them.

I am pretty certain that resistance gets easier with my Kickr the hotter it gets.

This always seemed like fair game- as the trainer gers hotter, the immediate environment gets hotter, the harder it would be to sustain the same power.
The fact that the resistance is easier offsets the difficulty associated with the heat.

Mine is definitely the opposite - the Kickr starts off in a cold room 20 watts easier than the Assioma, but after 45 minutes+, it's nearly the same. And I can def feel that 20 watt difference of increased difficulty in my case.