I also wanted to share one development - feedback from the wheels to the engine. When drive gear and clutch is on, not only does the engine accelerate/brake the wheels, but the wheels also affect the engine, do not they? There may be several solutions, for example, to calculate the torque from the traction force, and then apply it to the engine. But the most likely simple and effective way is this. We recalculate the angular velocity of the wheels back through the transmission and compare it with the engine speed. Multiply this difference by some coefficient (clutch friction coefficient?) And subtract the resulting number from the current engine speed. If the wheels spin faster, the number will turn out to be negative and minus the minus will give a plus, that is, the wheels will start to spin the engine. If the speed of the wheels is less, they will start to brake the engine. The implementation of this issue will simulate such an effect as if the car jumps on a bump and its wheels stop touching the road and the throttle pedal is pressed so far, then the engine no longer has resistance from the road and its speed instantly soars up. You can go further. We can consider, for example, the difference in speed in the clutch, and if the difference is too great for a very long time, then the clutch breaks down(As in those videos on YouTube X)). In other words, the engine speed in my project is considered in 2 functions - 1) the function where the engine spins itself up if the throttle is pressed, and brakes if the throttle is released. 2) function with differentials and feedback between the wheels and the motor