MOTORDOM

Greymouth Evening Star, 8 May 1931, Page 4

MOTORDOM

NEWS OF THE ROAD

(By

“Gearbox”)

HINTS ABOUT BRAKES

The importance of correct adjustI J ment of four-wheel automobile brakes .was recently demonstrated by tests conducted at the National Physical Laboratory, London. A working mod;el of a car was -used in the experiments. It was found that the model •kidded perfectly straight for four feet with all four brakes on and the wheels locked. With the two rear wheels locked the car skidded 9ft'. forward, and deviated Ift to one side, whilst with the two front wheels locked thej machine skidded sft forward and kept on a straight course. With both front and right-hand rear -wheel ■locked there was a skid of 4J feet with a slight deviation to one side. The investigation resulted in the following conclusions: The tendency to overturn is specially marked at high speeds with the following brake combinations—Two rear braked only in \ opqfration— a '‘-jgonal pair of brakes—and also when one front and two rear brakes are applied. In the case where the front brakes lock the wheels of a car, the driver has little or no control over the direction of travel so long as those wheels are locked. On the other hand, when the rear wheels lock, the stability of the motion is better under control. These experiments indicate the importance of correct brake adjustment.

Now-a-days, with high speeds and more road traffic the efficiency of automobile brakes becomes more important than ever. The standardising ;f ‘four-wheel brakes has given to motorists greater control over their vehicles, but at the same time has introduced a more intricate braking system when it calls for adjustment. The appearance of so many black smears of rubber on the surface of city streets is only too significant evidence of the number of automobiles that are running with unevenly adjusted brakes. Admittedly not all brake systems are easy to correctly adjust, an<J where there is any doubt in this respect it is advisable to let air experienced mehandle the job. For those who desire to handle the adjustment themselves, the Dunlop Co. suggest that the best way is to jack up both axles so that all wheels are free of the ground at the same time; then cut a strut to press down the brake pedal from the dash or from front of seat, whichever is the most convenient. Go to each wheel in turn and make the adjustment, so that you can just manage to turn the wheel by using your whole sfrength. Compensated brakes present the greatest dir-, Acuity and may make it necessary to go the round of the wheels several times. This is because individual adjustments affect the other brakes. In carrying., out such an adjustment it is well to remember that worn treads of tyres do not give the same road grip, as do covers with the patterned tread in good condition; also .that tyres should be evenly balanced as regards tread surface on the wheels of each axle. . >

IN CITY STREETS More effort is required to control and steer a car when travelling at low speeds in city traffic than when a moderate or fast pace is maintained on the open road, which sometimes accounts .for undue fatigue of which novices sometimes complain, while getting accustomed to driving. But a jnore common cause for fatigue is occasioned by the habit of gripping the steering wheel tightly at all times, so that the muscles of the hands and arms are continually under stress. This, of course, prevents the wheel from being moved freely find hinders the sensitive control necessary for accurate steering besides interfering with the natural tendency of the fro it wheels to return to normal straight position on* their own account afteifaking a curve. The facility for the front wheels to castor freely and with accuracy is essential both for safety and comfort of the driver, and therefore this action should not be hindered by undue interference bythe driver, as happens when the wheel is gripped too tightly.

BADGE OF DISGRACE r> —1 — 'An effort is being made in one c-f the States of America to bring irulegislation, which would compel'all persons convicted of reckless driving to display on the back and front of their cars red plates containing the letters “RD”, such plates to be carried on the back and front of the vehicle so long as the court might decide. The < intended effect of the badge of disgrace would be to warn the police and drivers of other cars, that the driver of the “Red Plated” car was a man that needed watching. > . AVOIDING TAXATION A novel suggestion to motorists about they could protest again 4 further taxation was contained in a letter received at a meeting of the committee of the Wellington Automobile Club on’Monday. The reading of the letter was greeted with some laughter bv the members..

“I am very pleased,” said the writer, “to observe that there is a movement on foot to secure the support of the Federated Automobile Associations throughout New Zealand in order to combat any increased tax burden that the Gpvernment may seek to impose on motorists. I take the liberty of suggesting that in the event 'of, a horse-power tax or a substantial further tax being put on petrol, an appeal be made to all members of the various clubs throughout New Zealand to store their cars, particularly those who use them for -leasurC/ only; that is, keep the cars in the garage and remove the wheels; which, I understand, is necessary to meet the technical requirements to avoid registration. This’would be done as a tangible protest against any such increased tax. The effect, as you will agree, would he such as to force the authorities !•> realise that motorists are tired of being made to bear the burden of taxation as a class.” “Wouldn’t that be a lock-out?” asked a member.

“It would be a knock-out,” suggested another member.

The letter was received

SPEED WOBBLE.

There are no doubt many motorists who have never experienced speed wobble with their cars; and when first faced with this peculiar development often in the short space of time devoted to wondering what has happened — a now the wobble to take complete control of the car and maybe with serious results. A speed wobble is simply an unpleasant “wiggle-waggle” of the front -wheels, but it usually develops without the least warning, and the disturbance is transmitted throughout the entire steering system, even up to the steering wheel itself. There is a cause for this trouble, which may be little known, and one that few drivers —even many with considerable experience—would give a moment’s thought to. Besides the common cause usually traced to -worn joints in the steering connections, it may lie directly with the front springs. In this way if the shackle bolts and their brackets have become overloose through wear—and those •on one spring may quite easily wear down before those on the other —a degree of play may be readily introduced, permitting one side of the front axle to be less rigidly mounted than the other, with the result that the wheel on the corresponding side has too much movement. Naturally this undue play

is inclined to develop as the speed of the car increases, until at a certain pace it has reached and passed the limit of safety. Then it forces the other front wheel to join in the revolt, and so the wobble commences. There is yet another likely reason for the introduction of speed wobble, and one that is generally the fault of the motorist himself. For instance, it has often bfien proved to have been caused by excess lubrication. This fact no doubt will cause a little surprise, but nevertheless it has been found that over-lubrication of the steering joints of the stub axle, track rod, and other steering pivots, may cause too free a movement; and lastly, the practice of fitting unequally shod wheels on the front axle (with . one good tyre and the other the tread , of which has worn down) is certainly asking, for wobble trouble. It ( stands the worn down cover —produc- . Ing in fact, the same effect as uneven- ‘ ly sized wheels on a single axle. As anyone may imagine, the larger wheel j will 1 always be trying to overrun the smaller. Speed wdbble starts, and un- ( reliable steering '-results, since the - driver’s attention must be devoted thewhole time to correction of the bias j of the larger wheel, whilst when < steering towards the side on which < the badly-shod wheel is mounted, un- j less extra care is taken, it will steer < too -readily that way, and may lead ] one into danger. On the other hand, . steering towards the side on which the j efficiently shod wheel is fitted will < prove stiff and generally difficult. Yet, - if any slackness in holding the steer- < ing wheel is permitted, the “wobbly i business” immediately takes control. j It is evident, therefore, that a speed j wobble is something to be avoided at ] all costs. z i -— 1

POWER TO WEIGHT RATIO There is plenty of scope for reducing the power ,to weight ration in automobile engines. The fact that the average automobile engine weighs about 121 b per horse power, and that, aeroplane power units have been brought as low as .781 b per h.p., indicates what a wide margin there is* between the powerweight of the two types of engines. Admittedly, they are made for different classes of work, but that- in itselb does not account for the difference. In the beginning, aero engines were little lighter than car engines, says the Dunlop bulletin. But technologists, , metallurgists, etc., have, by focussing their energies on the improvement < r aero engines, outstripped the efforts of those responsible for the motor car engine. So efficient, reliable, and light has the aero engine become, that little surprise would be occasioned should some of the leading automobile mann- , facturers, sooner cr later, use the aero < engine in their cars, after making any ( mechanical variations necessary for its use for work on the road. . j

Nowadays, with improvement n high-ways, better suspension of chassis, and larger and more resilient tyres, much' weight can be eliminated from the power unit- of the average motor car without in any way sacrificing its reliability and life. Malcolm Campbell’s feat in recording a speed of over four miles a minute with a Napiei* aero engine installed in his Dunlop shod “Blue Bird,” is a case in point. The engine weighed only 1140 lb., yet developed 1450 h.p., or .78 per h.p. Again the continued successes of the “baby” type of car in high speed tests on road and track has shown in no uncertain manner that engine weight can be elinfinated without reducing efficiency. '