By R. C. SYMONDSON
A Well-balanced Survey of How Fast Cars Should Steer and Corner.
Handling and qualities
MORE and more expressions do we meet the expression “understeer” and “oversteer,” and it seems
doubtful whether some people who freely use these expressions understand what they mean. One might indeed rudely assert that a shocking lot of nonsense has lately been talked and
written Before about going these any further, characteristicsther.
efore. let us attempt to define over-and understeer briefly. If a car is proceeding straight along a level road in no side wind and it is pushed sideways by a giant finger applied to its centre of gravity, it may turn towards the giant ; it is then said to “oversteer.” If it turns away from the push it is said to ‘” undert>teer.” A car wl1ich understeers tries to regain its former course (not its former track) if it is deflected therefrom (by bumps, by the driver turning the whee.I, or by a side wind-though in the last case the giant’s finger acts through the centre of [wind] pressure not the c. of g.). A car which understcers is, therefore, directionally stable and is easier for the driver to control than one which oversteers and, therefore, requires constant steering wheel movements to keep it on .its desired path.
Now it is by no means unknown for a car to understcer on the straight, but to overstcer when cornered fast. In this case the designer has built into it sufficient features to ensure that when running straight .the car will try to continue in a straight path, but has neglected to allow sufficiently for the fact that under severe cornering conditions t_he car will roll, leaf springs will bend sideways, shackles may do the same, rubber bushes will deflect and in general the location and direction of. the road wheels will be d.istorted from their designed positions to an extent and in a direction sufficient to make the car try to turn a sharper corner than the driver’s movement of the steering justifies. Cars which are a handful at speed on the straight but which corner well can also be called to mind, and these ill.istrate the opposite effect, i.e., they oversteer on the straight and understeer on corners.
Of course, skidding is not in itself anything to do with the. phenomenon under d.iscussion. It is a matter of adhesion ; a car which skids its tail round under the slightest provocation is a nuisance, but, until the breakaway occurs, it may well be an” understeerer.” Cars with no differential provide a good illustration of this.
It may be worth while to see if it is possible to lay down a list of desirable handling qualities for all cars. The cognoscenti and others may intcrjeet ” understeer ” and ” oversteer ” at appropriate intervals down the list.
(1) A car must go straight without undue attention at all speeds and on all surfaces.
(2) Road wheel reaction at the steering wheel must be no more than very slight.
(3) Backlash at steering wheel must he almost non-existent. (How lamentably few makers achieve this !)
(4) Steering must be reasonably high geared (very low gearing is dangerous in an’ emergency, apart from other considerations). Terms of reference relating turns of steering wheel to deflection in
degrees or road wheels are called for : the old ” num.ber of turns from lock to lock ,. is inadequate owing to variations in lock on different cars.
(5) Steering must be reasonably light. Again, accurate terms of reference are called for, e.g., foot pounds at steering wheel rim required to deflect road wheels to produce a given radial acceleration at a given car speed.
(6) Steering should have slight but not excessive self-return action.
(7)Steering must be positive at all speeds. To the driver there must be no apparent ” spring ” in the steering gear as a whole. Nor must he find it necessary to move the steering wheel a_ppreciably further to deflect the car a given amount when travelling fast than he does when travelling slowly; nor, again, must he find that a quick movement of the steering wheel fails for an interval of time to affect the course of the car.
(8) The steering must naturally never, never wobble or shimmy or tramp. It should be unnecessary to “wrestle ” with the steering wheel in order to make the car hold a desired course on a bend.
(9)The car should not roll appreciably. Rolling is always uncomfortable and, if not actually dangerous in an emergency, will spoil a car’s ability to ” dodge.”
(10) The car must have good adhesion, i.e., not skid easily. The back end should
break away just before the front end does so-but never the reverse, except perhaps under very heavy braking.
{11) The car must remain docile and controllable when the driver has made a misjudgment, e.g., coming too fast into a rough and badly cambered bend.
{12) The car must be able to ” dodge ” under the driver’s control, e.g., the car as a whole must react quickly and controllably when the driver swerves.
(13)The car must not feel” reluctant” to go round corners .. ·Nevertlieless·, ai; the car is cornered faster (i.e., as the ” breakaway ” point is more closely approached) the turning force required at the steering wheel must slightly increase. On no account must the driver find it necessary to do any ” unwinding ” of the steering wheel when the required rate of turning has been established. (It is here assumed that skidding has not been provoked.)
(14)When the car skids its rear wheels, it must be easy for the driver to correct the skid without calling for frenzied work. The car should not stop skidd.ing suddenlv nor with a lurch ; nor should it have a propensity for ” skidding the other way ” as soon as the initial skid is It will probably be fairly well agreed that we all want handling characteristics such as the foregoing. Many of them are interdependent. quite naturally. A good many of us know too that a very few of the cars produced in the ” pre-soft springing ” era could match up very well with these requirements (all right-I admit I am a Bugatti owner!) Of the remainder, few were very seriously unsafe because wheel travel was strictly linuted, especially at the front end of the car.
But now soft springing, with big lightly damped road wheel movements, has come to stay, and there is no question that both comfort and road adhesion at high speeds have in general improved as a result. The problem, therefore, is : can our desirable handling qualities be incorpJrate<l in a car with modern suspension? So far, with horribly few exceptions, designers have apparently been obsessed with the very real danger of producing a car with very soft springs and oversteering characteristics and have, therefore, provided us With unresponsive machines with spongy feeling steeringcars which have to be dragged round corners. They have thlL5 produced safe and well-sprung cars, but have robbed us of much-indeed, far too much.
Various devices have been adopted by designers to ensure “understeer.” One of these is, when using half-elliptic rear springs, to tilt the spring. upward towards the rear. Thus when the car rolls the ” outside ” -end of the axle is pulled forward as it rises : the inside end at the same time is pushed backwards as it drops. The axle is, therefore, pushed out of line in a direction which tries to prevent the car going round the corner. Another such device is to arrange the steering ” geometry ” so that when a front wheel rises on ” bun1p ” it turns slightly outwards and when it drops on rebound it turns slightly inwards. Thus when a car negotiates, say, a lefthand corner and commences to roll, the outside front wheel-turns, without instructions from the steering wheel as it were, slightly to the left. The inside front wheel similarly turns slightly to the left and the car, therefore, tries to straighten direction until the driver either applies more lock or slows down so that the car ceases to roll.
There is obviously much more than this in the design of the complete car affecting handling characteristics. But still, some of us may dare to think that tricks of this sort are rather beastly and, further, we may wonder whether the rapid tyre wear frequently experienced with post-war cars can be partly caused thereby. Especially as we are told that the lateral scrub of the front tyres on the road due to track variations with most modern suspension linkages is nothing we need worry about (though perhaps we do wonder about th.is too).
If the best of the ” cart spring ” handling characteristics could more frequently be combined with the modern ” flat ride ” I think a lot of us who are interested in driving would be much happier. As a step in this direction could someone whisper to design staffs that whilst we agree that understeer is better than -oversteer, nevertheless and notwithstanding, understeer is a bad fault and is one from which post-war cars suffer ?
