Ideally, the center-point of the turning circle would lie on the extension of the rear axle. The vehicle then passes through the curve, free of lateral forces, if each wheel finds itself on the curve-trajectory, whose center-point also lies on this extension. Due to the fact that the individual wheels pass through circles with differing diameters the result is also differences in the track which is followed by the wheels. Additionally shown in the picture is, that a greater track-width requires a larger toe angle difference.
The differing wheel-tracks are brought about through the steering trapezoid. The description 'steering trapezoid' is only applicable when the vehicle is moving in a straight line, because only then is this geometrical shape formed by the axle beam, the tie-rod and the steering rod. The greater the difference in length between the axle beam and the steering rod, the greater the track difference is when the steering wheel is turned. This is also valid for the cars of today, with up to three-part tie-rods and with no visible axle beam.
Actually, the relative steering angle should also become greater when the wheel base is increased. This however would assume a greater steering angle. Indeed, in practice e.g., with trucks, the frame would simply be lengthened. With an unchanged steering angle, the relative steering angle would in fact, become smaller.
Please take note, that in this case, we're dealing with computational or geometrical demands. If e.g., you were to move a modern vehicle to a suitable place in the showroom without starting the engine, you would mostly be confronted with considerable resistance and noises which would indicate, that the wheels are not quite following their planned trajectory.
Wheel-settings must be looked at as being dynamic. The elasticity of the chassis/suspension (even to a small degree in trucks) contributes to such a deliberate turning away from the geometrical provision. The fact that the outer-curve-wheel can be greater angled, to improve the slip-angle, may, in this case, serve as an example. 01/14