Re: turning radius 36ft fifth wheel
Welcome to the forum!
Theoretically, the minimum radius would be the distance between the axles and the center of the king pin.
If you're talking about how much room you'll need to turn that rig around, it would be the circle that is somewhat centered around the axles and extends out passed the side of your vehicle.
Like the old song says, "Give me 40 acres and I'll turn this rig around!"