November 1, 1920 



THE INDIA RUBBER WORLD 



87 



indicates another very feasible design to adapt the tandem axles. 

 Some of the advantages of the six-wheel truck over the regular 

 type of the same capacity, on 48 by 12-inch pneumatic tires and 

 on the regular equipment of solid tires, are that compared with 

 the pneumatic-tired four-wheel truck the saving by using four 

 smaller tires is sufficient to purchase three or four complete 

 spares, or approximately $S(X) per truck. Regarding case of han- 

 dling, each 40 by 8-inch tire weights only 119 pounds, whereas 

 each 48 by 12-inch tire weighs 398 pounds. Carrying a spare tire 



Fig. 5. A Fe.\sibi.e Design for Tandem Axles 



in each case, the reduction in axle cost, the use of two rear axles 

 in tandem results in the advantage that small axles are normally 

 in large production, with consequent lower costs, whereas large 

 sizes are made only in small quantities, with extremely high costs. 

 The actual saving amounts to about $120 per truck. As regards 

 weight saving, four 8-inch wheels with brake drums, etc., weigh 

 n pounds more than the same equipment for a 12-inch tire. The 

 total saving in weight is 814 pounds. 



Considering traction qualities, the area of contact of four 8- 

 inch pneumatic tires upon the road is about 27 per cent greater 

 than that of two 12-inch pneumatics. This additional surface, keep- 

 ing the tires from sinking in soft places, gives better traction 

 when most needed and, in ordinary service, the additional area 

 gives them a better chance to take hold. As compared to solid 

 tires in winter service, off of paved roads, the four pneumatic 

 tires have all of the advantage. 



The four-wheel combination has about the same advantageous 

 effects over single-axle construction that the pneumatic would 

 have over solid tires, in regard to economy. With the four- 

 wheel combination, when passing over an obstruction in the road, 

 the chassis is raised only one-half the distance it would be raised 

 in the regular type of construction. This reduces the accelera- 

 tion of bodies upon the chassis to one-fourth that with ordinary 



construction. Thus, by reducing shocks and vibration, the num- 

 ber and cost of repairs, due to crystallization, fatigue of metal 

 and the like, are reduced by a large percentage. The tandem 

 construction makes for such exceptional riding qualities that a 

 glass, filled to within an inch of the top with water and attached 

 to the rear of the six-wheel truck, lost none of the water even 

 when running over a decidedly rough road. 



The most destructive factors of the operation of vehicles upon 

 pavements are the wheel load and the wheel thrust. By re- 

 ferring to Fig. 6 one can see that a heavy wheel load causes the 

 road to fail by breaking through the pavement. If, as is the case 

 with the tandem coii-structioii, the wheel loads are cut in two, 

 the chances are that the wheels will seldom find spots in the 

 pavement weak enough to break through under this reduced load, 

 even if a S to 7-ton load be carried on the truck. 



The twin-axle combination has a decided advantage over both 

 regular pneumatic-tired and solid-tired types in that four brakes 

 of 21-inch diameter are used in place of two brakes of 21-inch 

 diameter. The six-wheel truck has a greater operating radius. 



Fig. 6. A He.wy Wheel Load Breaks Tiirouge the Pavement 



Pneumatic tires permit of an increase of average speed to double 

 that of solid tires, and the combination of four small tires on the 

 tandem rear-drive wheels wHll permit of increased minimum speeds 

 on bad roads. 



Pneumatic-Tire and Motor-Truck Development Experiences' 



By M. D. Scott" 



TABLE I gives a summary of the truck development obtained 

 over a period of two and one-half years. Picture a truck 

 weighing 15,800 pounds and carrying a pay load of 3,850 

 pounds, as against a truck weighing 8.000 pounds and carrying a 

 pay load of 7,000 pounds. This has all been brought about through 

 the use of pneumatic tires, thereby being able to carry a much 

 heavier load on a much lighter truck and, as pointed out before, 

 on a smaller sized tire, automatically increasing the earning power 

 of the truck. 



Table I. Summary of Pneumatic-Tire Accomplishment' 



I'eriod, 2>3 yeart 



But the end is not in siglit. We have succeeded only in prov- 

 ing that commercial trucks are uniformly built unnecessarily 

 heavy for use with pneumatic tires and that, when pneumatic 

 tires are used, weight can be materially reduced and the pay- 

 load capacity increased. We have also shown that the lessening 

 of the weight in turn allows the use of a smaller and less ex- 

 pensive tire for the increased pay load. We prove that more 

 can be carried on a light truck when it is hauled on air, and that 

 pneumatic tires permit a light truck to haul a larger load. This 

 all helps to sustain our contention that pneumatic-tired trucks will 

 use less gas, have smaller repair bills and generally give better 

 satisfaction. 



The following tabulation shows tlie performance of a fleet of 

 pneumatic-tired trucks covering a period of six months : 



^ Abstracted from Detroit-Cleveland Sections paper. The Journal of the 

 Society of Automotive Knpinccrs. October. 1920. 

 ' The Gocdycar Tire & Rubber Co.. Akron, Ohio. 



