Physcial Units of Wheel Collider Parameters

Hi everyone, we are using Unity wheel colliders in a mobile robot simulation for our research, and I am performing a study that compares performance of simulated robots with performance of real robots in challenging terrains.

I have attached a screenshot of the default wheel collider parameter values for our simulated robot wheels. My questions are:

  • What are the physical units (meters, Newtons, etc.) for each of these values?
  • Why were these default values chosen to be what they are?
  • The webpage for the Unity Wheel Colliders references the “slip-based tire friction model”, but I am having trouble locating substantial documentation on what exactly that is, from an engineering perspective - is anyone able to provide any more detailed documentation on this? (diagrams, equations, physical units of the slip, force, damper, spring, etc.)

I have done some searching on Unity documentation and forums, but haven’t been able to find answers there so far. Any help would be greatly appreciated.

This is a compilation of what is currently known about the WheelCollider: