As far as I know, they are not working with "race drivers" per se. However, they get a lot of data and feedback from manufacturers. But does it _really_ make a difference, I wonder ?
What matters more, I would say, is that: physics is done mainly by one guy (Aris), so instead of loosing time getting "a team" to work together, you get to actually spend it where it matters - in physics. And then, what's also important is that Aris himself races. Not professionally, but he has stressed a few cars on track - so he knows how it _should_ feel.
In the end, it's the overall feeling of the end product that matters - and AC feels great.
Can't say the same for pCars. And I was actually one of the original backers, and I wanted to be an awesome product. I have watched closely the development - and every iteration from the firsts alpha until the realeased version. The "math" side was there. The guys were doing huge efforts to nail the physics. However, something was flawed that made the whole feel very simcade in the end.
pCars, was only a success from a commercial point of view, but not at all as a "feels real" sim. Imo.

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Let's see what pC2 will bring. Wish them all the best honestly. Because aside from the physics, I actually enjoy(ed) the rest of the features.
