RELIABILITY.

Sun (Auckland), Volume I, Issue 237, 27 December 1927, Page 6

RELIABILITY.

EFFECT OF TYRES. COMPARISONS WITH OTHER TIMES, One of the most illuminating methods of studying automobile progress is provided by an examination of the varying complaints which follow changes in design. The modern motor-car, although differing only in deail construction from those manufactured 20 years ago, provides both driver and passenger with an entirely different type of general service. The ever-increasing demand for improvements in comfort and _ speed has made the modern car efficient, but it is efficient in a totally different manner to the most reliable cars of 1914.

Probably the most misunderstood, and at the same time one of the most important, links in the chain of reliability is the pneumatic tyres. Very few motorists have the slightest conception of the conditions under which a tyre operates, and the circumstances most liable to produce wear.

Tyre manufacture has reached a stage of extraordinary perfection. Tiie chemical and physical investigation of the properties of rubber, together with an unending series of experiments, has improved tyres out of all recognition. It is a fact, however, that motorists will be heard to remark that “the modern tyre does not always equal in mileage the older type,” particularly referring to those which are within the highpressure classification. Now the old-fashioned car, which was incapable of rapid acceleration or deceleration, subjected the tyre to a far nearer approach to pure rolling than can ever apply to the modern vehicle, which usually weights under 20 cwt, has powers of violent acceleration, and can maintain an average of 30 m.p.h. over good or bad roads, with an engine of 1500 c.c. It has recently been established that, under rolling contract alone, tyres are free from practically all signs of abrasion and wear; they will last up to 100,000 miles, and show but little effect through flexion, even when artificial road inequalities are included in the test. DRIVERS’ RESPONSIBILITY,

It is the conditions of use that affect the life of a tyre, and of these many conditions a certain number are definitely within control of the driver. When a car is used all the year round the tyres are subjected to strains of varying nature, but few drivers trouble to consider that tyre stresses-to-day are quite different from those encountered by tyres of three, or even two, years ago. # Quite apart from any increased vibration resulting from the general adoption of high speed engines, road speeds have enormously increased, and it is well known that this is a prime cause of tyre wear. With an increase of touring speeds it cannot be said that springing has improved proportionately. A bouncing .contact between road and tyre gives every opportunity for tyre wear, allows slip to take place, and tears particles from the rubber surface as the car progresses. The modern motorist expects far more than mere reliability from his tyres. He demands a vastly increased degree of comfort, which has naturally led to the redesigning of tyres to suit various makes of cars and different conditions of loading or spring action. Until quite recently motor manufacturers regarded the tj're as an afterthought; it would have appeared extraordinary to them if they, had been requested to vary any part’of the design or Wheel loading to suit the tyres alone. Yet this is a perfectly logical attitude. The low-pressure tyre is certainly more sensitive to alterations to “toein,” speed, violent braking and springing. Not one motorist in 10 will trouble to realise that a small alteration in pressure has little effect upon a highpressure tyre, but may cause a lowpressure tyre, with its increased area of contact, to work under totally different conditions ,to. those for which it was designed. If motor users required tyres for speed alone or for comfort alone, each of those conditions would he easy to satisfy.

The modern car must he both comfortable and speedy at the same time. The touring conditions of to-day are strenuous, and the damage which nie-chanicaV-or-drjving’ faults can cause is cumulative. A wheel which is liable to wobble does not necessarily render a car unsafe,, but it implies that a straight track is never maintained at speeds far below those liable to produce any damage or peculiarity of actual steering. A tyre with a quarter-inch error in the amount of “toe-in” provided is pushed 16 miles sideways for every 1000 miles of Its normal forward travel.

ON THEORY •We are told that any exercise which shakes up the liver is good fpr the general health. Then why complain about ruts and potholes on our roads. On this theory motorists and cyclists should be the hardest and healthiest race on earth. * * * “Compelling' motorists to exercise due care to avoid so far as possible the splashing of pedestrians meets with our entire approval.” Thus the South Island Motor Union:, in its comment on the proposed regulations. * * ♦ In its comments on the draft regulations under the Motor Vehicles Act, 1924, the committee set up by the South Island Motor Union expressed the [opinion that it was not necessary for la motor-cycle, .with or without a sideIcar attached, to be equipped with a reflector or periscope, , \