Changes v8.3b:
Reworked cabin behavior
Reworked seat behavior
New recommended settings

Physics was done in game v1.36 but it is very likely that it will work for newer versions of the game.
It is highly recommended to follow the Recommended settings, otherwise the result may be completely different.

This is  vision of physics and it may not coincide with reality

Installation:
copy the file to the "mod" folder and place it on top in the mod manager.

Recommended settings for v8.3 (can be changed in console or in config files):

g_cam_physics_value "1.0" (DEFAULT)
g_cam_physics "1" (DEFAULT)

g_cabin_suspension_stiffness "-1"
g_suspension_stiffness "0.3"
g_trailer_stability "0.5" (DEFAULT)
g_truck_stability "0.5" (DEFAULT)

g_brake_intensity "1.0" (DEFAULT)

residual_travel[] in chassis defs - 0.10 and 0.088 (DEFAULT)

ATTENTION!The g_cabin_suspension_stiffness parameter is set to "-1"! If you move the cabin suspension slider in the game's config, the parameter g_cabin_suspension_stiffness cannot become negative again! Then you have to set it to "-1" manually (in the console or in the profile's config.cfg file)! 

Credits:
knox_xss