[freebeard]

If I had pursued this further, I would have gone toward a Vespa motor scooter front axle, with it's side-arm brake and suspension.

I wasn't sure whether the offset between the horizontal and vertical axis is important to your design or not. I leaned toward an horizontal hinge at the bumper and another hinge at the axle. If it was to fold up, the wheel would be on a 4-bar linkage.

Another possibility might be two vertical hinges, with [a] control arm[s] to control the side-to-side excursions. I'm not sure how that one would back up, it might want to jack-knife.