Very interesting post from Aris (on FB):
Aristotelis Vasilakos :
The tyre model has been heavily reworked. 3 dimensional flex of footprint and sidewalls with specific rates for each axis that are also influenced by the pressure and temperature. Temperatures now have even more layers and even get affected by brakes heating. Pressure heat and wear do not only change a simple grip variation but also the actual behaviour of the tyre, affecting values of slipangle, slipratio, and the grip curve as a whole. You're not only feeling a different grip but a different response too. Tyre also has a different response depending on the different surfaces it touches.
The weather simulation is not a simple lower grip, but an actual water film layer with different depth. The tyres have algorithms that simulate the drainage of the water from the tyre, in order to keep the contact patch in..."contact" with the surface. If it succeeds, you get good grip, if not, the tyre "raises" over the water film and you get aquaplaning. That is what it makes wet driving so unpredictable. You don't have to deal just with a lower grip and that's it. You might think you got grip, push a bit more and instantly get a different behaviour on the same turn a lap before.
Many more big and smaller details got implemented and this obviously makes the fine tuning of the whole system, extremely delicate, considering that the rules predict just one compound for all cars/tracks combinations.
On top of that we have a brand new aero model coordinated by Stefano Casillo and created by Fernando Barbarossa our new physics developer. Much more complex, doesn't take into account different wings as single entities anymore, but a single aerodynamic object that gets affected by flow, and becomes very sensitive in pitch and yaw situations. 1-2mm ride height difference can be felt by good drivers and makes the setup a very complicated matter.
Because of that, we had to improve our suspension model. It now includes variable rate bumpstops that I can set with extreme precision to keep the car from pitching too much. Also new dampers with proper graph curves and not just 4 values. The bumpstops are quite complex so we're trying to figure out a way to make the setup screens better designed for the users.
We also have brand new TC and ABS algorithms, again more complicated than the original AC ones which by the way were an industry first at the time. Now we control slip and slide differently and even how much the engine cuts instead of on/off situations. Those maps alone can change quite a lot the behaviour of the car.
On top of that, add all the different dynamic grip and weather simulation and you can imagine that the possible combinations and situations where something can go wrong are quite a bit. We are also working in a condition that everything can change from a week to the other because of new features added and this means we might need to re do the physics of the cars.
Even BoP is different for each car and each track, and this is getting updated by SRO as we move from one track to the other...
So, I don't know where the 1.5 months per car comes from, as we keep working on all cars at the same time, so I can't really give an accurate estimation of how much time we spent on each car, surely Marco has this under control. But I can tell you that it has become extremely complex..