OK, I finally had some time to test the tyre wear issues. And it's just weird.
It kinda seems to depend more on the tyres than on car. I pulled up the official tyre app to compare the tyre wear and went hotlapping with different cars.
First I tried the Tatuus. With medium tyres, the tyre wear started at 92 and reached 100 on all four tyres in about 3 laps. Then it kinda sorta seemed to drop down more or less according to how the tyre wear bar in the official app went down. Then I changed the tyres on the car to softs. This time, the tyre wear on the fresh car out of the pit was 67 on all four tyres. It took them almost seven laps to get to 100 and then it began to fall down again mostly according to the bar in the official app. When the bar in the official app turned yellow, Sidekick was showing I believe around 60 on that tyre (scale 16).
Then I tried the MX5 Cup. The tyres again started at 92 and it took about three laps for them to get to 100. And then they just stayed there. I kept on hotlapping, hoping for some change, and it literally took me *an hour* (tyre wear 1x) before one of the tyres finally dropped from 100 to 98. It did it in one lap, too. Meanwhile, on the official app, the bar for this tyre was almost one quarter down (though still green) and the other three tyres were only slightly better. And obviously, the grip was very bad as well.
Then I took another car I drive a lot lately, the Porsche 911 RSR 3.0. This time, the tyre wear fresh out of the pit was showing 100 on all four tyres and the number dropping closely matched what the bar on the official app was doing.
Then I was running out of time, so I was spending less time with each tyre/car combo.
Ferrari LaFerrari with Trofeo Slick tyres. Start at 92, a few laps to get to 100 and then it seemed to stay there without dropping down, just like on the MX5. Changed the tyres to Road tyres, and just like on the Porsche, they started at 100 and then gradually seemed to be dropping down more or less OK.
And finally, the BMW Z4 with hard, medium and soft tyres. All three tyre types started at 92 wear and gradually got to 100. With hard tyres, it seemed to stay there - I did about 5 laps once they reached 100, so maybe it wasn't enough time. But the bar on the official app was definitely dropping. With medium and soft tyres, the wear seemed to be dropping, though not following the official app bar all too closely.
So yeah, I don't really get what's happening there. Not sure why with some cars/tyres, the tyre wear seems to be working as I would expect it to, and with others, it's acting weird to the point of pretty much not working at all with some combos.
And one more weird thing - doing all this and watching the indicators closely, I realized the brake temperature readout that is supposed to show up while braking (as I have it set up) doesn't work. Except - it works with the Porsche 911...
BTW, while going through my race recordings, I also found this race in the Tatuus with medium tyres (if I remember correctly) - and the tyre wear is all over the place there (watch the left rear tyre especially):
So...yeah...