It is certain that, with very few expensive exceptions, all normal cars are subject to either understeer or oversteer under certain road conditions. Can we then decide by considering the facts, which steering characteristic is the least desirable, and hence fall in or out with Dr Porsche?
Let us, then, first consider understeer. On any corner there is no force tending to move the rear of the car towards the inside of the curve, hence there must be movement of the front wheels outwards. This movement is at right angles to the wheels and therefore cannot be diminished by the driver at the steering wheel. By throttle adjustment, or braking, it may be possible to cause the rear wheels also to break away, but this only in the case of powerful cars and in certain circumstances. We can then assume that understeer is often completely uncontrollable and at all times increases the diameter of the turning circle, unless the engine power is sufficient, to balance the centrifugal forces.
Now let us consider oversteer. In this case, due usually to a rearward placing of the centre of gravity of the car, the back end tends to swing outwards. Immediately any movement takes place, the line of action of the tractive forces is towards the inside of the turning circle and the engine helps to maintain the turning circle diameter. At the same time the driver is in complete control of the front wheels, because they are not sliding, and by the correct adjustment of the steering the outward swing of the rear may be cancelled. Thus we can say that at all times oversteer is controllable, and under most conditions does not increase the diameter of the turning circle by an appreciable amount.
Going further, it is assured that when oversteer is inherent, the driver expects it and is always ready and able to correct it. However, in the case of understeer, control is impossible with a moderate engine, and as there is no automatic tendency for the car to correct, the break-away is sudden and complete.
I think, without doubt, that Dr Porsche wins the day.
I am, Yours, etc.,
John E Scanes. Stevenage.
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