The trick is to move the center of gravity below the ground contacts
You have to do this by playing tricks with the inertia tensor or “ghost” physical bodies.
The nice thing when you do this, is that the bike will balance on its own, and when you turn, it will automatically lean inwards (as a skilled rider would) beause the mass below the fulcrum is pendulum-ing outwards.
Two spheres will do great for this, as long as you can live with the diameter of those spheres out to the sides.