Which vehicle model is used to simulate vehicle dynamics in PhysX

I’m currently doing a research concerning the vehicle model PhysX is using in oder to simulate their vehicle dynamics. I’ve already found out, that one part is the rigid body dynamics simulation. But I am wondering, if they’re also using a two track- or multibody model to simulate the Vehicle Physics. I would be really thankful for any quick responses, ideas or hints regarding this topic.

I am also interested by the vehicle dynamic model PhysX is using. I would need to have an explicit form of the model because I want to use it in filtering methods to improve vehicle localization. I am currently trying to reverse engineer the source code to extract the dynamic model but it is quite a hard task.
I would be very thankful if somebody knows more about it, where to find a “better” description than in Vehicles — NVIDIA PhysX SDK 3.4.0 Documentation .