can anyone tell me whats spring rate??
like kgf/mm lbs/in?? what's all that mean?

 

It refers to how many kg's will compress a spring 1mm. This allows the stiffness to be gauged and gives a nice comparison method.

 

what's stiff and what's not (kg/mm)

 

There is no standard for what is stiff and what isn't. The weight of the car, desired unladen ride height, maximum compression force, minimum dynamic ride height, and other factors all determine what a good spring rate is (along with the necassary spring length).