The problem here is your root bone is below the wheels. I’m not 100% sure, but definately in UE3 the engine would consider the location of the root bone compared to the wheels as the “chassis height” which was a bit bonkers.
I’ve set up several vehicles in UE4 from Blender, and it’s always a pile of trial and error so get used to it never working right away. Lots of weird stuff factors in to whether the engine will consider the vehicle bottomed out or not. But in almost every case you want the root bone near the center of the vehicle, with the wheel bones lower down on the Z axis. I believe the root bone location is also taken into account for center of mass.
Also, you don’t need or want physics bodies on the wheels. Usually you’re only going to want one physics body applied to the root bone, I imagine having wheel bodies is what’s causing your car to launch into orbit, as the physics system tries to make sense of the bodies clipping into each other at the start.