Car Physics Bug After Unity 2022 to Unity 6 Upgrade - Momentary Speed Drop on Low-Mass Collision

After upgrading from Unity 2022 to Unity 6, my vehicle exhibits incorrect collision behavior. When the car collides with low-mass objects (that shouldn’t significantly affect vehicle speed), it momentarily almost stops for a couple of frames before returning to its previous speed. This occurs approximately 60% of collision instances.Expected Behavior:
Car should maintain consistent speed when hitting low-mass objects.Actual Behavior:

  • Car nearly stops for a couple of frames
  • Speed instantly returns to pre-collision velocity
  • Creates a “freezing” effect during collision
  • Sometimes it happens after a while, like 1 second after collision and after I’ve passed the object!

Untitled video - Made with Clipchamp

Technical Details:

  • Unity Version: 6000.0.32

Breakable map object every piece:
Physics Material & Mesh Collider Settings:

  • Dynamic Friction: 2
  • Static Friction: 2
  • Bounciness: 0
  • Friction Combine: Multiply
  • Bounce Combine: Minimum
  • Convex: true
  • CookingOptions: everything

Car:
Rigidbody Settings:

  • Mass: 1400
  • Linear Damping: 0
  • Angular Damping: 0.5
  • Collision Detection: Continuous Dynamic
  • Interpolate: Interpolate
  • Center of Mass: X:0, Y:0, Z:0
  • Use Gravity: Enabled
  • Automatic Tensor: Enabled

Mesh Collider:

  • Convex: Enabled
  • Layer: RCC
  • Layer Override Priority: 64
  • Material: RCCVehicleCollider

Physic Material

  • Dynamic Friction: 2
  • Static Friction: 2
  • Bounciness: 0
  • Friction Combine: Multiply
  • Bounce Combine: Minimum

Thanks for help

1 Like

This is the problem. Don’t use the Continuous Dynamic collision detection method.

A PhysX update in Unity 2022.3.8 changed how Continuous Dynamic works, and it seems this is the “by design” behavior now. More details: