The older FC's and 240SX's had a passive 4WS system that from what I understand used a system abnormally severe bump steer to cause toe changes. Most people who modify these cars will tell you that removing this system is one of the first things they do.
a few cars use an active 4-wheel-steering system - the honda prelude SI was available w/ it, as are a few current trucks & SUV's from General Motors.
from a performance stand point, 4WS systems used on production cars have no value. First off, the weight of the system is fairly significant. Secondly, the system is computer controlled, and the amount of left-right steering, as well as the direction, is dependent on speed.
At speeds below 30 mph, the rear wheels turn in the opposite direction from the front, like this:
FRONT
\\===\\
...........
...........
..........
//===//
REAR
The picture is exagerated, the movement of the rear tires is only a few degrees. This causes the rear to swing around faster, reducing the turning radius. A GMC Yukon with this system has the turing radius of a Honda Accord coupe.
However, the faster the vehicle goes, the rear tires deflect less and less. at about 40 mph, the 4WS system is pretty much disabled.
As you accelerate ABOVE 40 mph to highway speeds, the computer begins to turn the rear tires in the SAME direction as the front tires, like this:
\\===\\
...........
...........
...........
\\===\\
again, the rear tires don't turn as far....
this causes the vehicle to sort of "slew" sideways, great for changing lanes. It increases stability, reduces swaying in quick lane changes, and makes towing much easier when used on large trucks.
Again, from a performance standpoint, this would hurt high speed cornering. It would basically feel like an increase in understeer.
