I've used Michelins in the last 30 years, and they have been great! Yes, Costco has a Michelin replacement but it's the Michelins with only 40K mile warranty. For under $1K, it's not bad at all. One can use the Costco Tire Selector to find out if what's available in their area...
My R1S with 22-inch rims were updated last Friday night. I drove it the last two days on AP mode and yes, the ride feels posh in general that includes highways and light off-road. I also tested in on off/on ramps at ~45/50 mph and there was hardly any body lean. Posh ride to me is comparing...
I came across this article, and it was recently updated. I believe it will answer several questions posted on here and dispel the misconceptions as well.
How Do Rivian Brakes Work? (tirehungry.com)
We were in the area and since we were staying in Short Pump, VA, we decided to drop by the Rivian Service Center. Prior to our visit, we've watched a lot of you tube videos on performance and capabilities of the R1S. As opposed to the pictures posted here, the back lot was about 50% full...