Arizona republican., 1921-04-10

d tance, the tire must serve as a cushion between truck and road to protect the latter from the destruc- tive effect occasioned by the move ment of a heavy vehicle over hard surfaced road. Other attributes ot the ideal truck tire such as minimum effect on gasoline mileage, truck up-' i keep expenses and the like are fac tors of the above mentioned quail | ties.
 The pneumatic truck tire well fills | the first and fourth of these require ments-in other words, it serves as an efficient cushion between road and load and reduces the impact of high speed travel Unfortunately, however it absolutely fails to fulfill the requirements of the second and third conditions because of it's un- certain length of life, its liability to fail at crucial moments, thus entail ing a dangerous or expensive de- lay for replacement or repair, and It's inordinarily high initial cost which, in the larger sizes, will be. from 150 to 300 per cent greater than the more expensive grades of solid rubber or cushion type of tire. Obviously, the solid tire fails in those features in which the pneumatic tire is para mount, and operates to best ad- III lnOS0 QudiidSS III N1ilCL the pneumatic tire is most deficient.
 The destructive effect to road and load, of travel over rough roads, how ever, becomes only of importance at high speeds of truck operation. In like manner, the destructive effect of the heavy truck on a highway Is much greater at high speeds than at moderate rates of travel Conse- quently, the superior cushioning eff feet of the pneumatic tire is of prin- cipaI interest from the load, vehicle and road standpoint only to those operators who possess equipment capable of high speed transportation. Such equipment presuppoSes the use of a truck designed for speeds from 50 to 100 per cent greater than that recommended by the manufacturers of the average three to five-ton trucks of today. To be sure, the sub stitution of a A or 48-inch pneu- matic tire for a 40-inch solid in the larger sizes of trucks will increase the truck speed by a corresponding amount without causing the engine to race unduly, but will require power not developed by the ordinary engine. A careful study of the gear ratios and recommended engine speed limits of the majority of trucks, however, 1 has led us to the interesting conclu- SlOn lildC the IilCIedSSd dilOWdDle l speed made possible by the use of pneumatic truck tires will not ex- ceed 20 per cent. Thus a truck of a given size which may be restricted to fifteen miles per hour by it's maxi mum engine speed cannot be expected to render equal mechanical service on pneumatic tires at speeds in excess of eighteen miles per hour.
 So far as reliability and certainty
 
 there can be no comparison between solid and pneumatic tires. Passenger car experience has taught the motor ist that he lives in a constant state of uncertainty as to when his next blow out or puncture will occur. He may travel 10000 miles "on the orig inal air with no .mishap, but during that distance he cannot predict whether the next mile or the next 5000 miles will bring a puncture or a blowout. In like manner. there is no certainty to pneumatic truck tire mileage until after that mileage has been delivered. Pneumatic truck tires are made wonderfully strong but they sN'e also subjected to terrific pressures and overloads.
 The most enthusiastic pneumatic
 truck tire advocate does not, in al
 honesty, claim more than an average
 OI f,oOV lilies lTOHl tit6S
 with the necessity of tire remova
 for repair or replacement at leas
 once each month. With the labor oi
 two men required to change a 200
 pound, eight-inch tire, and three nnel
 and special appliances necessary tt handle the replacement of a 500 pound, 12-inch tire, pneumatic tir' change represents serious delay whicl may more than consume the Is or 2 ir,7ra rad n1 x1 possible by the use of such equip ment.
 Of course, truck design may b changed to permit of the use of nor powerful engines and truck con | struction of lighter weight--a combi l nation which may produce highe speed abilities on the road. Whe
 we reach this point, however, we ar l confronted with the dangers an
 complications arising from the law c
 physics to the effect that the dis
 tance required to bring a. movin
 vehicle to a stl) with brakes in per
 feet condition varies not directly a
 that speed, but rather as the squaT
 of the speed. Thus if a truck nor 8 mally travelling at 15 miles an hou
 can be brought to a stop within 2
 feet, that same truck traveIng at a
 miles an hour, even with brakes ar
 
 in which to be brought to a complet 4 stop.
 4 In the matter of initial cost, tf S pneumatic tire is considerably highC than the solid The table shown here with gives the comparative cost pt
 tire of pneumatic equipment capab Fl of carrying loads as indicated, ar
 the same capacity on one of the be S ter makes of semi solid or cUshiC II type of tires. The cost per mile hs & been figured on the very conserve q tive basis of 10000 miles without rt pair for the pneumatic (and this T considerably above the average SC
 vice obtained) and of 15,000 miles f VI the semi solid or cushion type q tire-a figure which is exceeded mo U often than not.
 E3 If such tire costs are taken in sH consideration, the operating costs
 some of the experimental trucl 8 especially developed to determine u ,N saving made possible by the use '3 pneumatic tires would be material s8 changed and the pneumatic tru, ' tire would be looked upon in VI proper light as an ideal equipme &1 for the especially designed tru
 Continued on Page Six)'