This is quite old now (2012) but directly from the developers on the subject
http://www.racedepartment.com/forum/thr ... 467/page-2
The tyre model is something Stefano has created ad hoc. It's based on "single slip profile" with flex, relaxation length, speed sensitive, and everything else you can immagine calculated dynamically and not in steady state.
It's a bit difficult to analyze with graphs and curves because everything is dynamic, but on the other hand it is extremely easy to tweak with relatively a small amount of variables and it is also difficult to do "stupid" things with it. As a result, even modders with low experience, will be able to do very good tyres for their cars, without messing around too much.
So the things you don't see, are difficult and already made by Stefano and to some extend me. The rest is easier to handle.
Most importantly, it gives an amazing feeling of being connected with the road, while at the same time staying always predictable without any moments of "wtf"
This is not our "NTM" that I mentioned in that tweet you've posted. That's an even more advanced tyre model that we are not going to use on v1.0. That one theoretically has some even more impressive potential, but we haven't even driven it, it's just equations and graphs for now (but very impressive hehe).