[-Joe]

The passive rear steer function is controlled by the "give" in the rubber bushes used to connect the wishbones. It will allow a small forward and back motion of the rear wheels.

In the Spitfire this maybe 1/2 centimeter at maximum. In the 75 it might be 1cm or so I guess.

With modern small cars they use trailing arms mounted solidly to the wheels center axle but with a rubbery mount to the body well forward of the center of the wheel. Which I feel is a bit uncivilised and takes getting used to but it does make these hot hatches handle really well.

The pivot point on 75 is closer to the center of the wheels so that the small rear steer characteristic is harder to detect.

The outward push is to do with the wishbones design for up and down suspension movement.

I guess the garage guy just doesnt understand suspension geometry in the same way as a car designer. If the rear wheels can independantly move back and forward even a little bit, that will help steer the car.