# Tire Slip Angle

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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...

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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 :)

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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!:)

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