Engine braking and inertia
This i believe is the biggest overlooked issue with physics, but surprisingly, is a crucial one.
As i work on new versions of my team's F1C historic F1 mods and conversions, i was surprised to discover how much more drivable the cars get once we fiddle (read lower) this value.
And i am not talking about setting it so low that it won't interfere with corner entry no, i am talking about power sliding or creating wheelspin out of a turn.
Let's think about the follwing example, you come out of a corner, you floor the throttle, the rear slides a little as you get wheelspin, you lift of half of the gas pedal and counter steer, and your car just slides even more to that side into a 180º stop.
All too familiar right? People at this point will quickly blame the tires. And rightly so, given the historical wooden feel of many simulations and mods of old. But is it the only thing to blame? It certainly isnt. I was once dumbstruck of a video of the suzuka hairpin, showing clearly Jean Alesi powersliding ALL THE WAY out of that corner, with the tail of his V12 1995 Ferrari hanging. It clearly showed me that sustained wheelspin on even a modern F1 was possible. But that wasn't happening in game, no matter how i fiddled with it, unless i would add unreasonable amounts of grip or downforce, and even then it was hard.
Until it struck me. I wasnt having problems when i floored the throttle initially. I was having problems when i lifted half of it to control the wheelspin. In that moment, the car would slide even more due to the back wheels literally braking on their own, and if i tried to counter steer, either it wouldnt make a difference, or the car would fishtail and send me out of the track.
So i tried to lower it a bit, influenced by some torque graphs i saw, and it was night and day. Suddenly counter steering started working, modulating the accelerator started working, and i could have a lot more wheelspin out of a corner without losing control.
Mind you, i don't know for certain what values of back torque are reasonable for certain X rpms in certain Y engine unless i have the real values, the values the modding and dev teams place on the cars might even be realistic, but the games don't handle them too well for what i see. This has something to do also with what inertia values the cars have, and how the physics engine of the sim cope with them.