When changing the mass property of a VehicleBody, the vehicle becomes strangely lighter with increased mass.
Using the mass property with another RigidBody yields perfect results in 1:1 scale metric system. For example, when calling add_central_force(direction * 9.8) on a RigidBody without global gravity, the RigidBody falls down to the ground in a realistic manner relative to its' mass in kilograms at what looks like Earth's gravity at roughly 9.8m/s.
However this does not work with a VehicleBody -- rather 10x the amount is what is needed for a similar result.