It's also worth mentioning that just like the other engines out there, the Madness engine is modular and can thus have all or some of it's parts rewritten from scratch, which is what has been done for instance for the tire model. It has literally zero % code from the Shift series. Same with the some of the other physics stuff like more complex suspension and differential model. Not sure about how
they've done the 4 wheel drive stuff but as I remember it they had to upgrade that stuff too.
The FFB topology is also completely new and comes now 100% straight from the tire+spindle arm (and the player gets to finetune the angle in car setup) into your wheel. They'll probably add the canned gear shifts and jolts things though.. but it will be possible to run 100% physics based FFB if you want to. The old Shift titles had a mix of straight-from-tire and "canned" effects, like slip angle (pretty much identical to what you can select in Assetto Corsa as an added effect), rumble strips, jolts and gear shifts.
On the graphics side of things, the most notable new addition is the weather/environment simulation which is brand new.
The AI is also brand spanking new and the early signs are very promising!!