LACK OF ADHESION

Evening Star, Issue 21881, 19 November 1934, Page 15

LACK OF ADHESION

DEFECT IN GAR DESIGN la the ‘ Sydney Morning Herald ’ recently appeared a couple of articles by William M'Neill, who holds that the basic cause of ear accidents is a latent, defect in car construction. Although it has always existed, he says, it has never been so pronounced as it is today. Mr M'Neill says that the defect is two-fold. The tractive-adhesion of motor cars is neither its purpose, nor is it maintainable on the open road. Tractive-adhesion is the effect of the friction or weight-pres-sure of the vehicle on the road for the purpose of converting the enginepower into propulsion and for the maintenance of steering direction. Its efficiency depends upon its ability to prevent the road wheels spinning and side-slipping on the road and to keep the steering under the driver’s control. It should, bo the foundation of the design, of all self-propelled vehicles, because safety, efficiency, and comfort depend upon its due and proper application, but in motor car design it is ignored, with the result that cars pass out of the drivers control to the danger of all road users, f It is true that all motor vehicles, according to their total weight, have some degree of tractive-adhesion, but safety demands that that weight not only shall .be proportionate to speed and other conditions of road performance, but that" its distribution upon the road wheels shall comply with certain recognised necessities. The factors governing the Jaw of tractive-adhesion arc top technical to be entered upon, but the lay mind will grasp its importance from three evident'facts—viz.:— 1. There cannot be the same degree of safety in each of two cars travelling over the same road surface at the same speed,-if the total weight of one car is tiyice that of the other ; further, if the two cars are of equal Weight, there cannot be the same degree of safety if the driving wheels of one car are carrying a greater weight than those :of thepthcrcar. ; 2. As the speed of a car iifcreases, the more easily, is its direction deflected by extraneous influences, such ns are produced by road inequalities, _ centrifugal force, sudden acceleration of speed or. brake application. The lighter the weight of the car the more easily is its. .direction deflected by these influences.

: • 3.- ,Tho, exiremo ■ flexibility and resilience of modern car springs and tyres must, under frequent conditions of service, render tractive-adhesion not only unreliable, but often nugatory.

To place the, public in possession of vehicles having sufficient engine power to propel them at high speeds, regardless of their weight and other factors of tractive-adhesion, is a sufficiently dangerous custom, but when the construction of such vehicles permits oven that haphazard degree of tractive-ad-hesiqn_ to b’e lost under frequent road conditions, it is not surprising that accidents should occur so frequently. If the driving and leading-wheels of locomotives did not carry permanently the great weight of the boilers, etc., or if their springs were more flexible and the rails less smooth, neither safety nor efficiency would be expected, and public inquiry into the disastrous results would soon produce a rectification of the defects.

It is important to understand that the pneumatic tyro is merely a spring with similar “ pitch and toss ” defects to those in a steel spring. The only difference is that whilst the resilience of the steel, spring can be controlled, the resilience of the pneumatic spring (tyre) is definitely uncontrollable. For years_ manufacturers have been increasing the flexibility of springs and tyres in order to increase their shock absorbing'properties, regardless of the fact that the greater the amount of road-shock-force they absorb the greater i.q the strength of their rebound action, which in turn produces greater oscillation and loss of tractiveadhesion. This is the cause of the majority of serious accidents and the discomfort of motoring. It requires intimate knowledge of the- motor industry -to understand the norsistenco of.manufacturers, year after rear, pursuing increased flexibility of ' springs and. tyres, whilst at the same time the whole world is lamenting the huge casualty lists of the disastrous insults of that flexibility.

The unpalatable truth may savour of heresy; nevertheless, facts lead to the logical assumption that certain so-called improvements arc making cars more and more unsafe to drive on the open road. This is particularly evident in regard to uncontrolled flexible springs and uncontrollable flexible tyres which permit loss of tractive-ad-hesion more readily, and therefore more often. _ The problem cannot bo solved by fitting additional shock absorbers, because it is due entirely to the efficiency of the shock absorbers, springs, and tyres. It cannot be emphasised too strongly that safety and comfort exist only whilst tractive-adhesion is maintained. If the average vehicle is deficient in tractive-adhesion it is greater reason for maintaining that which does exist, ami this can be done by'applying the obvious remedy—viz.: I: Eliminate excessive tyro resilience by keeping tyre pressures high enough to prevent it. Tyre resilience is definitely uncontrollable. 2. Eliminate excessive spring resilience by using au effective system of spring control. Spring resilience is definitely controllable, and can now be accomplished without adversely affecting the efficiency of the most flexible springs.

The only real shock absorbers on a car are the .springs, tyros, and upholstery. As the resilience of tyres cannot be controlled, it is not belittling

their value to state that their safe practical utility is limited to a comparatively, small degree of flexibility. On the other hand the resilience of springs can be controlled, therefore, springs should absorb all the road shock thfit is too great to be, absorbed by the tyres; but to do this safely their resilience must be under effectively control.