In a car game, it seems like increasing the mass much is having trivial effect on physics! Even on increasing the mass quite a much, as soon as the car collides with a wall collider, it springs up in the air like anything – as if it’s having a mass like a foot ball!
Gravity is also proper, but can’t get what could probably be the reason for this weird behaviour.
Can any one throw some light on this?
I think the problem you are having is do to the scale of you objects.
Try making them larger. If that doesn’t work then try smaller.
If even that doesn’t work then there is something really weird going on.
Scale and Drag are parameters that have been making problems to me. 
try Connor’s tip
The reality of vehicles is that when one hits a wall there is some “give” in the metal of the vehicle. You are asking a physics engine to replicate that without the give. This is like throwing a metal ball against a metal wall. since the forces are not adequate for either to deform against the other surface then your result is much like you say “a football.”
In the Physx world all objects are strangely solid. They do not have any “give” at all. Even if you were to program “give” into the model, (via scripting to make it deform) the physics result would still not be what you want, because it takes a collision to set off those scripts.
I guess the point I am making is… You probably will never get it right, so do some tricks to get it close. 
Do you mean that mass depends on dimension instead of just mass property of rigidbody?
Well, i’ve already tried that and because of resizing had to adjust colliders also to prevent flip-off and all.
Scale is currently (1,1,1) only, if nothing works out then yes, i will have to drag the ‘drag’ into picture 
Yes BigMisterB, i understand rigidbody concept in physics, and you are right, if normal things don’t work out then tweaks and tricks are final resorts
Thanks all
First i think you’ve got to use/make a physics material that bounces like you need it to.
If you need things to fall faster you need to rescale all of your project. It works best if you think of one unit being one meter.
Drag will only slow down falling and will not speed it up.
Mass is not used in falling, its only used for collisions between rigid bodies. Like if i have a rigid body with a mass of 2 and a rigid body with a mass of 0.5 the body with more mass will push the other object and the object with less mass will resist less. Size does come into play though, and i think the term mass is improperly used by unity where it should be called density.
If you want to avoid rescaling your project, you could try instead setting gravity to whatever 9.8 meters would be in your projects scale. Ultimately though at the start of a project you should make sure all your units are good for this sort of thing, sucks having to rescale late on.
Yes BDev, i agree that mass is not used in falling since gravity is independent of mass. Masses are considered for collisions and forces.
Thanks BDev, that was useful. It seems i will have to resort to some work around
thanks UDev. Good answer.
I’m reescaling all times the projects but now i know that 1 unit is 1 meter i will try to think it before start new one project.