Wheel collider sinking in the ground problem

Hi there!
I have a serious problem with my game. I am writing a trials remake and everything works fine, except for the wheelcollider. It behaves fine, when I ride on flat surface. When I fall and land not parallel to the ground, the wheelcollider sinks in the ground, then it bounces my motorbike away. I also tried to add extra sphere colider to prevent from sinking in the ground, increasing fixed timestep, but nothing helped.

I dont event have to go very fast to make this happen.
Please, help!

 

Hello.
From what I've seen , the problem is in the way Wheelcollider works, or rather essentially what it is, is not a wheel but only a raycast down to detect ground and simulate suspension spring effect. So when it's on flat ground, everything is fine because the ray goes down perpendicularly with the ground. But when the ray and the ground are not perpendicular, the above happens.
I have been only using wheelcollider for cars with fairly low normal angle, so I'm afraid I don't know the best solution.
One thing I can suggest is to have a script that rotates the WheelCollider according to the relative angle between the bike heading and the ground.

 

That could work, but there is just one problem, the wheelcollider cant be rotated. It looks like it raytraces -y in world space.