hi, for collision events I would stick to regular physics hit events and maybe do some filtering. getting the impact velocity/normal should give some information about the feedback scale.
about bumps it could be handled in a couple of ways but hard to tell which would work best. I would probably try to get each wheels local Z velocity and consider it a bump when it reaches a certain threshold. you could check wheel.getRayHit or wheel.getSuspensionCompressedLength etc. to calculate the vertical velocity. make sure you add some averaging to filter noisy data.