THE HONGKONG TELEGRAPH. MOTORING SUPPLEMENT, SATURDAY, SEPTEMBER 6. 1930.
TESTING FOR WHEEL WOBBLE. Analysing the Causes and Effects.
AN INTERESTING INSTALLATION. During recent years the most on another. Personally, I began difficult problem with which to think it must be caused by some At the time manufacturers of motor cars have obscure bacteria!
at its had to contend is without doubt, when the epidemic was the phenomenon known as "wheel height, people were rather free in wobble." My recollection "is that blaming the makers of tyres. for the first serious epidemic of wheel they said that the softer tyre with wobble began to show on cars its larger deflection encouraged some six or seven years ago wheel wobble to begin, whilst the writes Montague Tombs in the addition to the unsprung weight Autocar, at about the time when of the front axle due to the front speeds had begun to go up, wheel brakes made it much worse. possibly as the result of the better
Experimental Work by Tyre control afforded by four wheel
Makers.
before the War.
can
the vertical centre line of the hub, an alteration automatically would, haye been made in the amount of caster action given by the inclined swivel pins of the front axle, which easter action, of course, has a quite considerable bearing on the behaviour of the vehicle's wheels during steering.
When the car is in position a spring-loaded pencil is attached to of the front the centre of one wheel hub Caps. This pencil 2 sheet of paper bears upon
two drums
stretched between rotated at n definite speed by
clockwork, so that the pencil draws upon the paper a record of the movement of the hub. A second pencil is operated from a speed indicator worked in con-
Junction with the electric" motor, whereby another line is traced brakes and when tyres were In self-defence, therefore, the upon the paper, giving an Indica- changed from the original high pressures to the lower pressures tyre makers themselves had to do tion of the equivalent road speed which since have undoubtedly a great deal of experimental work of the car at any moment during A speed indicator proved beneficial. for punctures to find out what really was the the test. and bursts have now become cause of the bother, and much attached to the electric motor rarities on any save old cars. But time and money have been spent shows the operators the equivalent wheel wobble as an ailment of the by the Dunlop Rubber Company in speed of the car in miles an hour.
carrying out research work. This The Plant In Action. motor car is nothing new.
cases of has culminated in the installation
In action the wheel wobble- remember having seen
plant is violent wobbles and flaps long of a special plant at Fort Dunlop, testing
immensely which enables any car suffering Interesting even thrilling to from wheel wobble to be tested watch. The electric motor is The Two Different kinds
safely under minute observation, started up, and the front wheels
duta that definite There are, it seems, two kinds of so
be begin to revolve as the drums wheel wobble-a low-speed wobble obtained on cause and effect. rotate. At first the wheels remain and a high-speed wobble. The Basically, the plant consists of perfectly steadily in contnet, and low-speed phenomenon is usually a large hollow ramp on to which then, perhaps when 55-60 m.p.h. set up by traversing a series of the motor car is driven. Within is reached, the tremor begins. It pot-holes, and does not matter the ramp is a stout shaft carrying increases until it reaches a con- very much.
This occurrence is a pair of large-diameter plain siderable violence, the wheels most likely to be due to incorrect drums, and this shafts is driven by bouncing up and down clear of adjustment or excessivi wear in a powerful electric motor con- the drums, and rocking violently the steering gear. It fellowa, too, trolled as to speed of revolution from side to side and around the that a car that can produce a low-by a rheostat. The distance apart steering pivots, so that the steer- speed wouble will very likely for the rollers can be adjusted to ing wheel of the car is kicking so possess a high-speed wobble of a suit the track of any car. The vigorously that it cannot be held. considerable intensity. On the vehicle la manoeuvred into posi-The front springs flex and twist, other hand, severe high-speed [tion and secured so that the front and the frame of the car twists wobble may be encountered on of contact being carefully set so from end to end in the most extra- that it lies vertically beneath the ordinary way, whilst the radiator It seems that the great difficulty centre of the hub, which provision and bonnet appear as if they were in dealing with high-speed wobble is, of course, necessary in order about to part company with one has been that the disease has had to make sure that conditions on another and with the car. That so many possible causes, and steps the road are correctly reproduced; is wheel wobble, a savage force taken to cure it on one car have if the point of contact were a which occura for no apparent sometimes made it actually worse little in advance or a little behind reason, and which appears to be,
well-nigh uncontrollable.
new cors.
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1 must not be thought, of courke, that wheel wobble will attack absolutely any car at any moment. Correct design in every detail and essential can prevent wheel wobble from ever occurring in any conditions other than extreme wear or complete lack of adjustment. It is, nevertheless, a chastening experience to see, as I have seen, a violent wheel wobble in full swing on this testing machine, produced by a particular car which I know has, when in normal condition, an eminently respectable character and no Ay- away habils.
a
It is also rather uncanny to see wheel wobble start up for apparently no reason whatever. In the pass it was easy enough to believe that a wheel wobble might hê caused by front wheels striking
a series of pot-holes or irregulari- ties in the road surface, which set up some vibratory movement cor- responding to the periodicity of some other element in the car's construction. The preconceived idea is badly shaken when a high- speed wheel wobble is seen to start on the equivalent of a per- fectly smooth road surface. Effect of Pressure and Absorbers.
During my visit to the installa- tion some interesting tests were made showing the influence of type pressures and of shock absorbers upon a wheel wobble in a car specially picked for the pur- pose. The first test was made with the tyres at a pressure of 30 lb. and with the shock absorbers slacked right off. A violent wheel
wobble occurred at 55 m.p.h. Then, the front shock absorbers were screwed up to their normal adjustment, and the test was ze- The wheel wobble took peated. place again at 55 m.p.h., but its intensity was reduced to the point where It was no longer vicious, but merely unpleasant.
it was
After that the tyres were pump- ed up to a higher pressure, 40 lb. to the square inch. This had the effect of raising very consider. ably the speed at which the wheel wobble took place. Previously, the critical speed was 56 m.p.h.. now raised to 67 m.p.h.; and, to my surprise, when it did come at 67 m.p.h.. it was a great deal more severe than it had been with the lower tyre pressure at 56 m.p.h. The lesson from this is that hard tyres will cure a wheel wobble; they will only cause it to take place at a higher speed, and the harder the tyres the greater the violence when the wobble comes.
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On March 10, 1980, Cecil Hawley, Director of Texaco National Road Re ports, left New York for Los Angeles in a stock model Buick Roadster, He was back in New York March 26 after travel- ́ ling 10,243 miles in a total elapsed time of 16 days 13 hours and 36 minutes. Every precaution was taken to observe all traffic rules and regulations. An average speed of 29.35 miles per hour was maintained. This was a business trip, testing the qualities of current model Buicks and the new Texaco Motor Oll. No attempt whatever was made to establish a record.
*
Five months later, Mr. Hawley again left New York on a round trip dash to Los Angeles (California) and re- turn to New York... This time Mr. Hawley was driving a stock model 118". wheelbase Buick Coupe. Hawley's total time from New York to Los Angeles and return was five days, 21' hours and 44 minutes. This record is more than 17 hours faster than the swiftest Transcon- tinental Trains. The previous record held by, Cannonball Baker, the famous
cross-country driver, was broken by more than 15 hours. Mr. Hawley's stock model Buicks were fueled and lubricated by the new and better Texaco gasoline and the new Texaco golden oil
4
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