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Watch Your Tyre Costs

28th January 1938
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Page 14, 28th January 1938 — Watch Your Tyre Costs
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Which of the following most accurately describes the problem?

AFTER 15 years spent in selling and servicing tyres, I have come to the conclusion that, as a whole, they do not give more than 85 per cent, of the mileage that is built into them. The odd 15 per cent. is lost in many ways, some arising accidentally, some from mechanical causes, and others through absolute ignorance, carelessness and neglect.

The loss in individual cases is often severe—tyres completely wrecked after insignificant mileages. In other instances, the cover is subjected to conditions of slightly accelerated wear, which would escape the notice of anyone who did not know for just what to look, • Money Wasted • The tyre maker sells a high-" builtin" mileage, for which we pay. We pay for what the tyre is capable of doing, but do we get that maximum? It is extremely doubtful.

No, the fortunate operators are comparatively few. Most of us think that we are obtaining the maximum and we are content; but actually we are probably losing 15 per cent. or more of life.

Fifteen per cent. loss of mile

age is 15 per cent, loss of capital outlay, which, on the cost of a set of 32 by 6 heavy-duty covers, is about £7.

Small fleet owners receive a discount of 15 per cent, on their tyres, but if they lose 15 per cent. of mileage, it is equivalent to paying retail price for them.

•• Beyond Control • How shall we avoid this loss? It can be done only by systematically correcting those influences which make for rapid wear or premature failure. Some of these, including accidental damage, are beyond control, but they do not constitute a great proportion of the whole.

They comprise the cuts, concussion bursts, etc., that anyone is liable to sustain through sheer bad luck. Little can be done to prevent them, although it is worth noting that a tyre run at correct pressure is more likely to resist these forms of damage than one that is wrongly inflated.

The greatest loss of tyre mile age on commercial vehicles is sustained through overloading, underinflation and misalignment, These, the major causes, are all easily controllable.

B10 There is no reason why a good vehicle should not carry a fair percentage of overload if it be equipped for the job. Many fleet owners fit helper springs to assist the road springs to bear the extra weight, but it never enters their heads to do something about the tyres.

To most of them, a tyre is an unknown quantity of uncertain strength. They do not realize that each cover has a definite limit of carrying capacity, which is stated (in cwt.) in the price list. If this load be exceeded, the tyre will fail, just as in the case of a fuse wire subjected to an excessive amperage.

A tyre is an uncomplaining sufferer. It does not knock or pink, after the manner of an engine that is being strained to its limits, but the damage is, nevertheless, being done. Instead of waiting for audible or visible signs of suffering, we must nurse the patient from the beginning.

In the previous article, details were given of the carrying capacities of the most popular sizes of tyre. If you find that your vehicle is under-tyred, you must fit an oversize to obtain maximum mileage. Do not labour under the delusion that the stress of overloading can be eased by increasing the tyre pressures above the normal. Overinflation is injurious.

Many operators are well acquainted with the fact that they are overloading their tyres and are aware that they are losing tyre mileage by so doing. They have calculated (to their own satisfaction) that the extra pay-load compensates for the loss of tyre life.

This is a question on which no definite ruling can be given, owing to the wide disparity of opinion as to what constitutes an overload. Moreover, of course, the rate of pay must be taken into account. This question can be settled only by the operator himself, but the figures given below may give him some guidance.

It is a fact that in cases of overloading the loss of tyre mileage is greater, in proportion, than the percentage of overload, as the following table shows:— Percentage Percentage Loss

Overload. of Tyre Life. 5 10 10 18 20 30 30 40 50 60

It will be quite obvious from these figures that overloading calls for careful consideration, and should on no account be undertaken until the consequent loss has been worked out.

• Effects Similar • There is a certain similarity between underinflation and overloading, for in each case the volume of air is insufficient to carry the load. In the case of underinflation, there is an adequate receptacle which has not been. properly filled, whereas when a vehicle is overloaded the receptacle is inadequate to accommodate the air necessary to bear the load.

Both causes have the same effect. The tyre flexes unduly and great heat is generated, thus resulting in rapid tread wear and frequent carcase failure, to say nothing of the increased vulnerability of the cover to accidental damage.

Pressures should be checked at least every week, an operation that can be carried out only with a proper gauge. Slovenliness in pressure checking is common. Even to-day there are many drivers who judge their tyre pressures by eye; if there appears to be no undue flexing of the wall, they are quite satisfied. A margin of error of as much as 50 per cent, is quite common in such cases.

• Maintain Pressure It is important that the correct pressure, as specified' in the price list, be accurately maintained, and at no time should it be allowed to drop more than 10 per cent, below that recommended by the maker.

Loss of air may be due to valve leaks, slight punctures, or air shrinkage. Any tyre that loses more than 15 per cent. of pressure per week, when working under normal conditions, should be suspected of a puncture or valve trouble.

These slow leaks are devastating in their effect and are much more to be avoided than a rapid puncture. The driver, having just had the tyres inflated, goes forth with a full load feeling confident that everything is in order. Slowly, imperceptibly, the tyre is losing air, perhaps to the extent of 60 per cent. per day, yet because the loss is so gradual, it remains unsuspected and does great harm.

, I have known many tyres to be ruined by under-inflation within 24 hours of having been inflated, and always it is due to the unsuspected slow leak.

• Check Daily •

Vehicles engaged on comparatively light town work are not so liable to suffer from this trouble, as their tyres are subjected to a fairly regular casual supervision, but bn long-distance and heavy-haulage lorries, a pressure gauge should always be carried and a check should be made daily.

A great deal of trouble can be eliminated by regular attention to valves. Air is often lost by valve cores becoming worn or dirty. Renew these whenever necessary and always fit a valve cap. By so doing you prevent grit and damp from affecting the core, and the cap in itself is an extra air retainer.

I come now to the third of the major evils previously mentioned— misalignment. It would be safe to wager that out of 100 vehicles selected at random, nine or 1G would be found to suffer from misalignment in a greater or lesser degree. This fault may cause' a loss of tyre mileage of anything from 10 per cent. to 70 per cent., or even more.

I have known a brand-new tyre to be worn down trithe can

vas in three weeks. It was 21 ins. out of line.

Misalignment has the effect of dragging one or other of the front tyres in a sidewise direction, which results in the tread being " scuffed" off. Friction, except that caused by ordinary rolling and braking resistance, should be non-existent on front tyres, but misalignment introduces a third and considerable friction, which will dispose of much more tread rubber than the other two.

The signs of this trouble, apart from rapid tread wear, are sharp " feathered " edges on the tread blocks of the tyre. The idea that misalignment causes the tread to wear more rapidly on one side than on the other is false. This is a question of wheel camber. A tyre that is out of line will often wear evenly across the tread. The damage is so easily sustained that it is seldbm appreciated. A sharp tap on the kerb when pulling into the 'gutter is quite sufficient to put the wheel out to a large degree. DelaY is expensive. In extreme cases, it is possible to lose two or three potential miles for every mile travelled'.

The vehicle maker, in the handbook, states the correct amount of toe-in. This reading is taken when the lorry is at a standstill and it is calculated to allow of the wheels splaying out to parallel when tra.velling at normal speeds.

• Gauge Essentials

To read the setting, a proper gauge is necessary. It is useless to attempt to measure it with lengths of string, strips of wood, etc. Even when trouble is not suspected, it is advisable to take a reading every month, for it is often difficult to detect slight misalignment by inspection of the tyres. The' job takes Only three minutes or so.

Any Vehicle is liable to be suffering from any one, or all three, of these major causes of tyre wear. Careful selection of equipment will eliminate failure from overloading, but this initial precaution is almost useless is backed up by regular and systematic attention to the maintenance of correct air pressures and

alignment. L. V. B.


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