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Putting the Tractor "On Air" and what it has achieved

30th June 1939, Page 70
30th June 1939
Page 70
Page 71
Page 70, 30th June 1939 — Putting the Tractor "On Air" and what it has achieved
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The Pneumatic' Tyre Has Won Its Way to Success for Tractor and Other Duties and Has Brought Many Advantages to Farmer and Driver In Its Train

IN little more than five years, the pneumatic tyre has secured a hold upon the tractor industry which is significant in attesting to the all-round success of the rubbertyred wheel. At first, the innovation was regarded with the usual scepticism to which most refinements in agricultural-engineering practice are subjected, but a growing appreciation of the practical utility of the pneumatic has already overcome a great deal of this prejudice.

The proportion of tractors being sold " on air" has shown a steady rise during the past three years and, in many districts, has already exceeded 50 per cent, of the total. This is the more remarkable in face of the substantially higher cost of a rubber-tyred tractor, as against the same model on steel wheels. This, commonly, amounts to something in the region of £50 which, on a machine costing, perhaps, less than £200, is sufficient to make most buyers think twice before specifying the air-tyred model.

The far-seeing farmer, however, realizes that, in many circumstances, he is getting better value in the rubber-tyrecl tractor, even at the higher price, as compared with one on steel wheels, chiefly because he will get out of it more work at lower cost. How is this done?

Regarding the tractor merely as a machine for hauling a plough, it may appear that the steel wheel with spade lugs. or cleats is the most practical type, and that pneumatics are merely a luxury. It is true that one can work almost anywhere on such wheels on this class of work, but it is, nevertheless, a fact that several disadvantages are present.

Eyed the process of moving from one field to another may necessitate the fitting of road bands over the lugs, a job causing considerable loss of time. If the land be hard, the machine, when in work, is subject to a great deal of excessive vibration. When the land is soft much power is absorbed, due to the sinkage of the lugs into the soil and their withdrawal as the tractor moves forward.

On such work alone, then, the pneumatic tyre offers substantial advantages, due to reduced rolling resistance and less vibration. These two factors are responsible for savings in fuel consumption (provided the effective diameter of the rubber tyres be not less than that of the steel wheels); fewer breakages due to vibration; muchimproved working conditions for the driver (the less fatigue he experiences the better his daily output of work).

The air tyre has some distinct advantages over the standard steel wheel for cultivation work, beyond what has already been mentioned. There are frequent occasions, in some districts, when it is difficult to gain adhesion with c2S steel wheels, owing to the yielding nature of the soil. This is commonly encountered on sandy land. Here, it is possible with pneumatics at low pressure to secure a footing, due to the flexible nature of the tyre, and to carry on where steel wheels would simply spin.

Tractor work does not stop short at cultivation, and the most striking effect of the air tyre is to render the tractor suitable for a great variety of jobs for which it is not fitted on steel wheels. This means to say that a rubber-tyred tractor will replace more horses than the older type. All kinds of farm haulage over the land and on the road fall to the lot of pneumatic-tyred machines, whilst they are popular for use in mowing on land that must not be damaged by solid tyres. This is especially true in cutting short grass for artificial drying. This is a job where considerable power is needed to cut and load the grass automatically, and horse teams or steel-tyred machines would be quite unsuitable. Pneumatic tyres have exerted a big influence on design, that is also having its reactions on agricultural implernen...

It has been found that larger wheels with a big arc of contact help to solve the problem of securing traction when soil conditions are difficult. They also fit in with other requirements, such as high clearance, for row-crop tractors. These larger-diameter tyres Mean fewer engine revolutions for a given distance of travel and this factor shares with over rolling resistance in reducing fuel consumption by an appreciable and satisfactory margin.

There is now a considerable range of different tractor-tyre sizes on this market, a compared with the limited selection when such equipment was first introduced. The 11.25 by 24 size has sold in large numbers for mediumsize .general-purpose tractors, but there is now a general tendency to displace this in favour of a 28-in. tyre on the same machines, since the 24-in. wheel is undoubtedly too small for the best results on this class of machine. For row-crop work on tractors in the same power range (motors of 20 to 30 hp.) a common size of tyre now adopted is the ii by 36, which is giving good nil-round results.

The application of pneumatics to the larger %%heel-type tractors, developing 40 h.!). or more on the belt, was at first thought not to be practicable, but opinion has changed in view of the fact that such machines are operating successfully on such equipment. The size of tyre adopted is usually a 12.75 by 32, and with such equipment an outfit will handle a four-furrow plough on heavy land or haul a full-size thresh

lug machine on the road without any difficulty at all.

Tyre makers have devoted intensive research to the production of hard-wearing tyres that are also noteworthy for self-cleaning action and gripping qualities, so that it may almost be said that whenever the ground is fit to work, a rubber-tyred tractor will work it. The life of such tyre.-, when properly cared for, would appear to be more than equal to the normal life of the tractor.

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