THE GROWING PNEUMATIC TYRE
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Conclusions Which Have Been Arrived At in the States Concerning the Employment of Pneumatics for Commercial Vehicle Work.
E REFERRED, in an editorial article in our issue of January 27th; to the fact that de-velopments in the employment of the pneumatic principle in tyres for heavy motor vehicles for .commercial work have Made eonsiderably greater advances in America than they have in this country. No fewer than 37 Makers of chassis suitable for commereial-vehicle work have adopted.pneunna.tic tyres as standard equipment on their productions ; whilst in our reference to the recent New York Show of commercial-motor vehicles (appearing .elsewhere in this issue); there is a short description of the new Packard 3-tonner which, being fitted on all wheels, With. the giant pneumatic tyres, is .shown to be equipped in consequence with an engine powerful enough for a h-tonner.
But for the war, developments in. the use of the pneumatic tyre in this country ,would have been equally advanced, but more has been done in the way of experimental work than has:ever been recorded, the BritishthanufaCturer al-ways being fhr more reticent concerning his work,aims and intentions than the American.
One of the chief. authorities in the States on .the sabjeet of prreurrihtic.tyres and wheel,eqUipMent.fOr commercial-motOr Vehicles is:Mr;--J.-.E.. Hale, .who is the.--ehief tyre designer -fot. the cleodyear: Tyre and Rubber Co.-,.and...we. prepOse.to,-epitomize here some of _the remarks -which he:ireeently addressed.,to.the members of -the_Automsitie Metal Wheel Association for the -purpose of enlightening them upon the need of the ease in wheel,design, so far as concerns the welfire.-of,the tyreErigith which they are to be fitted Mr. Hale is emphatio2in his assertion that the change from solids to pneumatics,' as the tyre "equipment on commercial vehicles, makes such remarkable improvements in vehicle operation from many points' of view, that it is really an epoch-marking transition in motor-vehicle deVelopment. The im proved cushioning qualities saves the mechanism of the vehicle and conserves the health of the driver ; it increases the traction of the driving wheels and the speed of operation, whilst the greater all-round usee• fulness, due to all these causes, puts the commercial. motor vehicle on an entirely different plane.
The elimination of the destructive effects of bad roads on the chassis mechanism results, so far as the designer' of the vehicle.is .concerned, in making it possible for him to 'clOsign his chassis very IntU41lighter ; hundreds of pounds of metal can be taken from all parts, weight can be-euttint of the frame, the transmission, the body; 'the 'power plant and thewheels. Mr. Hale prophesicd.-tht,-wheels could' be made much lighter than-anbotly had ever. -dreamed of making them and stiill'be!'a.idOqua.,te•-strengtli, and his propheey,has already'cOne true in that all:minium cast wheels are now _being ,employed, 'which; 'Whilst saving' 5.0: per "cent, of the wheel' weight, promise to give strength equal to that of the:Wel:Wheel. These aluminium-. wheels were shown for -the -first.: time at the New York Show, and are referred to in our article
on that exhibition. . ,
There is, according to this authority, nothing..inherent in pneurnatick,res for commercial-motor vehicles which makes them difficult to handle. The tyres, in a general way, are typical of those in use on passenger cars, although, from the tyre designer's point of view, the structure of the tyre does require some• refinements and special treatment, but these differenee.s are not apparent to the person untutored in tyre construction. The tyres are subject to the same sort of shortcomings in the matter of tyre failure, and the inflation pressure under which they are operated. is greater, whilst being rather expensive and being subjected to rougher conditions of wear and tear, they require the best possible treatment in order to give
a low tyre-mileage cost.
The problem of fitting the proper size to the vehicle and of ensuring that the tyres are not overloaded, is infinitely greater than that which the Use of pneumatic tyres on passenger cars .now presents, because, undoubtedly, the ear owner is now fully educated to the value of over-size tyres, although, for the sake of cheapness, ear manufacturers themselves have, largely, been at fault in using inadequate tyre Sizes.Great pains, however, must be taken in connection with pneumatic tyres on commercial -vehicles to ensure the use of tyres of adequate size in order to protect the new development.
A good deal is being done by way of co--operation between tyre•manufacturers and vehicle Producers to secure a -standa,rdized table of vehicle lay sizes and tyre equipment, the vehicles being recognized by their carrying capa.city and a tyre equipment which is-adequate being specified. The educational process is now being extended to the Wheel makers in order to secure standardization of wheels for the different models. This work is being pushed forward in America,and it is sincerely to be hoped that the standardization committee of the S.M.M.. and T. will push, in the same direction, the good work Which it has already done in the matter of establishing adequate standards. A complication in the matter of pneumaticequipment for commercial vehicles which' does. not
in that for passenger cars, is the need for the use of different sized tyres on the front and the rear wheels. In the ease of passenger crs, an all-round size tyre is quite a satisfactory equipment, and only one size of spare need be carried, but, in the case of the heavY vehicle, and particularly those in the higher categories, the difference of weight on the front arid
rear axles makes it desiral)le that there should be a difference in the tyre sizes. So fay as the 3-4-ton vehicle is concerned, 5-in. tyres all round is a satisfactory' arrangement,. 'although 4-in.-tyres wouldbe adequate for the front wheels, but, in any case, the
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tyres on the rear wheel a should no be less than the 5-in. named. In the case.of the 1-t n vehicle, a good equipment for the rear is the 6-in. yre, and 41-in. is adequate, for the front, but a 6-in. tyre on the front would not be regarded as' a .satisfactory job. On a 4---ton lorry the tyre sizes should be 7-in, on the rear and 4i-in. on the front. .0nthe 2-ton vehicle they should be 8-in, on the rear and either -5-in, or 6-in. on the front.
The development of pneumatica'for. commercial
vehicles would seem, according to Mr. Hale, to be fairly well worked out for the equipment of vehicles. up to and including the 2-ton job, but, beyond that, theProposition., although partially developed, is still unsettled'. He is bold enough, however, to predict that the tyres, which will fit wheels built for 8-in. tyres, will be quite satisfactory. on 3-ton and 3-ton vehicles (rear wheels, of course), whilst 10-in, tyres will be Used on the rear wheels of 546n vehicles. The development Work which has been done up to the present has been with larger sizes, up to as much as 12-in, on the rear of 5-ton vehicles, so that, if a 10-in. .tyre shouldeventually prove to be adequate, this should be very satisfactory showing, if only on the two grounds of cheaper cost and the reduction of weight. .
There is' a good deal of controversy as-to the best way of . employing pneumatic tyres whether they should be used with a detachable rim (the flanges being detachable as in the case of the Moseley rim, well known in this country), or whether they should he oar. Tied on demountable runs. So far as the larger sizes of Vehicles are concerned, Mr. Hale's experience leads him to Favour the use of the detachable equipment, his opinion being based on the fact that it is useless to carry round superfluous weight, or to Pay extra costs.
A good many factors come into consideration in deciding this point, such as the question of weight in handling when changingtyres, and the weight which has to be carried as dead weight on the vehicle. It is easier also to handle the quick detachable tyre, particularly on a meta.l. wheel, where the thin felloe makes it easy to locate the valve and pull it through, although it is imperative that the vehicle should be equipped with a pciwer pump. The metal wheel, for many reasons, and particularly when used in connection with the power pump, Means the maximum of simplicity, lightness and strength, whilst it is easier work to change a tyre on a .quick detachable rim it merely takes a .little longer time than in, changing one on a demountable rim, and, of course, there is less weight to carry with.the spare. One a the matters which wheel engineers have to keep prominently before them is the need for ado qua,te strength in the rim portions ot the wheel, to resist the tremendous bursting preslaire exerted by the air in the tyre. The sPecifications of the American Government for tyres called fortyres to stand a 350 lb bursting pressure in order to be satisfactory, and it is natural that the same figure should be used for the wheels. Taking the hydrostatic tyre pressure at ..350 111.to the' square inch, the force acting horizontally on the pneumatic tyre rims tending to blow the side rings off, in each of the different tyre sizes, is . shown in the following table:— In many of the wheels which have been tested considerable .LweaktieS's was found,' some Of them not standing half the pressure set out in the table.;."Wheel manufacturers have been very glad to-know -the results: of there tests andto set to work to correct the faults..--...The point ihaa,to be taken .seriously fox, if anything 'should. happen 'to the rim:portion:of :the -wheel So tha the ritoirk, blew off,, it Would Jae_ very disastrous to lire and jlimb, because, of the 'tremendous amount or energy stored up by the air in thetyre. Another matter of importance in the matter of design of 'Wh6C1S is the neeeSsity oriiiaadng the rim portion of tlic wheel so that it .shall conform strictlywith the standard toIefarices'PreSCribed."" Thia hecessary so that' cutting and other bad, troiible,s shall not develop in the lyres. The 'earning' of the whoa makea it possible, in aiming -di 'a 6traiig forth of rim which shall gii,e.a.moderafelY,quiek'detahability, -Co split the rim eirciuriferentialt in Stieh a''''r(raY that the two halves of!the Tim map-be,.bialted together.
There is a"goed deal:to-be-done kftheidevelopriaent stage in the raatter of finding'a:goodipOsition for the valve, The growing use of the internal gear_ drive (where the housing for these sears is sufficiently large to interfere_ with the _valve in its _normal: position,), and, also, .,the splitting of the rim circipoitexentiOlY call for some new arrangement, and, ope oithéinost promising goliiflohs is an, offset, valve, which _brinks the valve out near the side of the rim fiistead of ,down through the centre line. Another important point is the desirability of treat, ing the 'piTtion of the wheel on which the Ore seats with some rust proofing compound.