How to properly scale with Colliders?

Hey, hope I can find some help here. I bought an asset for a modular race track, but it's way too small and when i scale the whole track, i get invisible bumps and walls here and there, also my car gets a bit wild and sticky when colliding with another object. it doesn't do that when the track is unscaled. Mesh looks fine to me. shrinking the car is not a good option for me either. it's a prefab with box colliders on straights and mesh colliders for the rest of the children. And yes, I'm new to this, but it's almost the only thing that prevents me from further level design. please, i'm going nuts here. :D