The equation for slip angle is:

https://en.wikipedia.org/wiki/Slip_angle

slip_angle = atan(speed_y / abs(speed_x))

However, I am not sure how does the speed_x exactly work. Is it the wheel's motion in longitudal direction ir maybe it's wheels effective speed(angular velocity * radius)? The second version seems to work like it does in other physics engine(the handbrake reduces the lateral friction), however, I'm still not sure if it is really the right way...

What's the velocity of a point at the contact patch? Vcp = Vcar + WheelDirection * WheelAngularVel * WheelRadius.

1) When a wheel is free-rolling, it means the velocity at the contact patch is zero. Meaning the rotation and direction of the wheel cancels out the car linear travel of motion exactly. Vcp = 0.

2) The steering starts turning the wheel. The wheel direction is not aligned with Vcar. So Vcp will now be != 0.

3) when you apply the handbrake the wheel rotation is now Zero. Therefore Vcp = Vcar.

4) when you apply too much power, the angular velocity of the wheel becomes greater than Vcar. It's the opposite effect.

To calculate speed_y and speed_x, it's Vcp, but projected along the wheel direction vector, and the other component, perpendicular to it.

That's the simplest version of tire dynamics, of course :)

What's the velocity of a point at the contact patch? Vcp = Vcar + WheelDirection * WheelAngularVel * WheelRadius.

1) When a wheel is free-rolling, it means the velocity at the contact patch is zero. Meaning the rotation and direction of the wheel cancels out the car linear travel of motion exactly. Vcp = 0.

2) The steering starts turning the wheel. The wheel direction is not aligned with Vcar. So Vcp will now be != 0.

3) when you apply the handbrake the wheel rotation is now Zero. Therefore Vcp = Vcar.

4) when you apply too much power, the angular velocity of the wheel becomes greater than Vcar. It's the opposite effect.

To calculate speed_y and speed_x, it's Vcp, but projected along the wheel direction vector, and the other component, perpendicular to it.

That's the simplest version of tire dynamics, of course :)

So it's the both things I mentioned added together? Interesting to know. I'll try plugging this in to see how it works, thank you!:)