Factors that Govern
Page 33
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Tyre Equipment on Light Vans
Our Contributor Outlines Some of the Chief Factors of Tyre Use Peculiar to Small Vehicles and Stresses the Importance of Fitting Equipment that is Adequate for the Loads that Have to be Carried
rIN glancing through my previous
contributions I find that I have dealt mainly with those tyces used on heavy goods vehicles, and have to some extent neglected the equipment used on light vans. Perhaps this is partly excusable when one considers the greater difficulties which attend the use of giant tyres, and the far greater financial outlay involved.
Their importance to the operator looms very large, and, to some, they represent a never-ending story of high expense and low mileage. This is due to the exacting conditions under which they are used, conditions which the lighter stuff is rarely required to face. It is not unnatural that giant tyres, with all their attendant problems, should receive the most attention.
How Giant Tyre Equipment is Determined
What is the difference, you may alk, between a giant tyre and any other type? Just where is the dividing line between the two classes?
It is -quite simple. Any tyre which is made purely and simply for a cornmercial-vehiele chassis is a giant tyre. It is not interchangeable with any car tyre, for instance, Generally speaking, too, this class of • equipment is found on all goods vehicles from 1-tonners upwards.
On the 5-10-cwt. type of van, which is usually based on a car chassis, a car tyre is used. This, then, is the dividing line. From 1-tanners upwards the tyre is a purely commercial model, specially built to face the hard work, which lies ahead, but on the smaller vehicles an ordinary car tyre is called upon to do commercial work. Thus, the tyres -which were intended to equip 8 h.p., 10 h.p., and 12 h.p. cars are pressed into service on vans of 5-10-cwt. capacity.
A Factor that is Ignored by the Maker It is unfortunate that the vehicle manufacturers do not see fit to increase the tyre •equipment in Order to make it capable of doing the job which is expected of it. Very few do. Although there is no actual commercial-vehicle model of tyre in these small sizes it would, nevertheless, be quite easy to increase the tyre size, and, therefore, its carrying capacity, from the existing range. But, apparently this is not to be. The light van on the car chassis is usually turned out with exactly the same tyres as the equivalent model of car.
In many cases, surprisingly enough, this arrangement works quite well. The butcher, the grocer, the baker. and similar tradesmen, provided that • they keep within reasonable limits, do not experience much trouble. Their short local deliveries, with not-too heavy loads, do not impose too great a strain on the tyre equipment.
At the other extreme we have the builders, plumbers, milkmen, etc. Operators in this class are frequently not prepared to invest in one of the heavier models of vehicle, and they use extremely light lorries for transporting considerable loads. This overloading, although it may have no apparent effect on the vehicle itself, will cause frequent tyre failures, but the difficulty can be overcome if it be attacked from the proper angle.
The Tyre Must Be Built for Its Mission
The first pant–to establish is this. In nine such eases out of ten, where troublo is experienced, it is due entirely to the fact that the original• tyre equipment is inadequate for its mission in life. No matter how respected its maker's name, no matter how conscientiously it is inflated and cared for, it is bound to collapse prematurely if it be subjected to repeated overloading. You cannot make a pony do the work of a cart-horse—at least, not for long.
So the first step in the right direction is to depart from the manufacturer's specification and fit an oversize tyre.
Against this procedure there is the well-worn argument that the maker is best judge of what is most suitable for his vehicles. This is mainly true, but it must be borne in mind that the manufacturer is often limited as to tyre equipment by reasons of economy 'n production costs, and, perhaps, a desire to standardize. Moreover, the original equipment is intended to cope only with normal conditions for which the vehicle is designed. If conditions be abnormal the tyres must be adjusted accordingly. Carrying capacity is raised with
increases in size. Tyre sizes for any given rim diameter increase in steps of .25 or .so of an inch. Thus we have such increases in sections as 4.50, 4.75, 5.00, 5.25, 5.50, 5.75 (16-in, rims only), 6.00, etc.
Simple Matter to Increase the Tyre Size Almost any vehicle will stand an increase to the next greater tyre size, and most of them will take two sizes greater. Thus, a 5.00-17 tyre can be used to replace a 4.50-17, a 5.75-16 will replace a 5.50-16, and so on. These increases in tyre size do Lot necessarily entail a change of wheel equipment and often do not require a change of inner tube, because nowadays tubes are made • to be equally suitable for two or three sizes.
Before making the conversion it is necessary to check clearances to the nearest fouling point. Clearances should be measured with the vehicle laden with its usual load, and front wheels should be checked with full lock in both directions. Bear in mind the amount of increase in the oversize tyres as compared with the originals.
The minimum lateral clearances with the oversize tyres should be (a) 4 In. to any fixed part which will not come nearer to the tyre when the vehicle is in motion (such as springs, brake rods, etc.), and (b) 1 in. to any moving parts such as rnudguards, body, etc.
Another Method of Raising Tyre Efficiency So much for the oversize tyre. There is still another way in which tyre efficiency can be raised, and that is by fitting a heavy-duty cover in place of the standard equipment. Heavy-duty covers are usually of six-ply construction, as compared with the four plies of the standard grade, and they have an additional 25 per cent, effective tread rubber. Of course, the absolutely ideal arrangement is to invest in an oversize tyre of heavy-duty quality, thus securing two great improvements embodied in one tyre.
Nothing has been said about .cost.
There is not much to say. It boils • down to this. If you buy oversize equipment you have to pay for it— naturally. But if you do not buy it you still have to pay for it in lost mileage, failures, and repeated outlays on inadequate tyres. The initial outlay for the oversize is greater, of course, but the ultimate cost is about the same. The saving is effected in the elimination of trouble and the increased efficiency of the vehicle. L.V.B.