I'm not entirely clear on how the tyres work, but I understand that there are x number of flat sections, so the tyre is not round (which would explain the choppiness).
I've posted a couple of times about the odd instability, and about how the actual driving, particularly on roads is not very good or worth bothering with for long, at the moment, even if it's a bit of fun for a while. Usually met with the usual tunnel-vision response from "Defenders Of The Devs" (defenders).
Reading your thread in the Beam forum, atledrier, I'm still not entirely sure how the tyre works. Someone says 12 sided "wheels" act like 24 sided "wheels" because one side is rotated compared to the other. What does that mean? That half the left side is out of line with the right? Do the tyres end up running on the points of the shape rather than the flat face, as they would in real-life?
It all seems irrecoverably messed up and all this talk of wheels being too heavy if they're rounder and so on just seems to suggest that it's impossible to do anything serious with the tyres in this engine.
Still, good crashes and junk.