Mechanical linkages for this seem to have a dual ratio in the rear. For the first few degrees of steering, the rear wheels steer with the front, crab walking the vehicle, as the steering is turned further, the rear straightens before turning counter to the front, performing as a shorter wheelbase. Obviously this is done a a simple solution to provide in phase at low steering input for high speeds, then counter phase for high steering input at low speeds. However, it seems that it would be more advantageous to do the opposite at higher speeds. Counter steer the rear initially in order to rotate it into what would be an oversteer condition for a 2 wheel steering vehicle, and then to turn the wheels in phase and slightly crab walk the vehicle through the turn. This would introduce a sideslip angle onto the rear axle and then utilize the available traction of the rear to balance the reduce the horizontal forces on the front axle. The Ackerman ratio seems to be a nightmare as well, with the center of rotation constantly moving around.
Mechanical linkages for this seem to have a dual ratio in the rear. For the first few degrees of steering, the rear wheels steer with the front, crab walking the vehicle, as the steering is turned further, the rear straightens before turning counter to the front, performing as a shorter wheelbase. Obviously this is done a a simple solution to provide in phase at low steering input for high speeds, then counter phase for high steering input at low speeds.
However, it seems that it would be more advantageous to do the opposite at higher speeds. Counter steer the rear initially in order to rotate it into what would be an oversteer condition for a 2 wheel steering vehicle, and then to turn the wheels in phase and slightly crab walk the vehicle through the turn. This would introduce a sideslip angle onto the rear axle and then utilize the available traction of the rear to balance the reduce the horizontal forces on the front axle.
The Ackerman ratio seems to be a nightmare as well, with the center of rotation constantly moving around.