656 



THE INDIA RUBBER WORLD 



June 1. 1921 



15 per cent greater than the actual wheel load. The four dif- ing conditions, especially the condition of speed and of tire equip- 

 fercnt solid tires which were used show very clearly the eflfect mcnt. This statement refers lo impacts only. It should be 

 of the condition of the tire. Tire Xo. 17 gave some very high noted in particular tiiat a light truck running at high speed will 



Public Roads 



Fig. 5. Comparisox of Tires — 5-Tox 

 Truck K — Lo.'M), 5 Tons 



MILCS Kit HOUR 



Fig. 6. Comp.^rison of Trucks vs. Fig. 7. Comparison of Trucks — Tire De- 

 Speed — Two 5;/2-Ton Trucks flections — All 2-Inch Obstructions 



impact values even at 12 miles per hour. This tire was badly 

 worn, having a thickness of only one-fourth inch above the rim. 

 The other solid tires gave impact values somewhat in proportion 

 to their deflection or condition. The results shown by tires 

 Nos. 10 and 11 indicate the usual impact values that may be 

 expected with good solid tire equipment, while the results shown 

 by tires Nos. 4 and 17 show the increase or extreme values that 

 may be expected from the same truck when the tires are in a 

 badly worn condition. 



Fig. 4 is a comparison between the effects of solid and pneu- 

 matic tires. The truck was 5^-ton capacity loaded with lYz 

 tons. This graph shows the very great cushioning effect of 

 pneumatic tires in comparison with solid tires. In this case a 

 4-inch obstruction was used during the test with the pneumatic 

 tires, and the effect was much less than when using a solid tire 

 on }^-inch, or 1-inch, or 2-inch obstruction. The efifect of the 

 air pressure in the pneumatic tires upon the value of the im- 

 pact force is also shown. 



Fig. 5 shows a comparison of tires ; that in general the mag- 

 nitude of the impact force is dependent upon the condition and 

 deflection of the tire. It shows graphically the wide variation 

 in impact values that may be expected from the same truck 

 equipped with tires of different conditions. 



Fig. 6 shows a comparison between trucks. Two S'/2-ton 

 trucks were each loaded so that the total rear wheel load was 

 the same in each case. Truck A had an unsprung weight of 

 1,950 pounds and truck K had an unsprung weight of 1,300 

 pounds. Both trucks were equipped with ihe same set of tires. 

 This comparison shows the effect of unsprung weight upon the 

 impact value. It is very clear that the truck having the lighter 

 unsprmig weight produced the smaller impact values under the 

 conditions of this test. 



Fig. 7. This graph shows the possil)Ie impact values 

 which may be obtained by using trucks of different capacities. 

 It is clear that the light truck, W, if run at a sufficient speed, 

 may give impact values as high as a heavy truck, when run at 

 the ordinary truck speeds of 8 to 10 miles an hour. These im- 

 pact values were all obtained from a 2-inch obstruction. This 

 graph shows that it cannot be said that a heavy truck always 

 gives the highest impact values, without slating several qualify- 



produce large impacts only occasionally and never very heavy 

 load pressures ; while a heavy truck will produce in addition to 

 impacts a continuous heavy pressure on the road surface. 



As might be expected, the pneumatic tire is given the front 

 rank. Its maximum impact value is about 1^ times the static 

 load at one rear wheel, with an average value of not more than 

 25 per cent. For a solid tire passing over a 1-inch obstruction 

 at 16 miles an hour the impact value may be as high as seven 

 times the load at one rear wheel and the average value about 

 4 times the static load. Truck speed has an important influence 

 on the degree of impact force, the impact increasing with the 

 speed in the following approximate ratio : Solid tires, 10 to 

 100 per cent ; cushion tires, 10 to 75 per cent ; and pneumatic 

 tires, to 10 per cent. 



A SIMPLE BUFFING CONE 



How tlie finishing touches are put to a tire made by tlic unit 



molded system 

 is shown in the 

 accompanying 

 illustration, and 

 simple as the 

 process is, it is 

 very effective. 



The essential 

 apparatus is a 

 truncated cone, 

 shaped not un- 

 like a n exag- 

 gerated butter- 

 tub, mounted on 

 a short, project- 

 ing shaft. On 

 t Ii i s tapering 

 form the work- 

 man places a 



Tire Finishing Drum 



casing of any size, and while it is being revolved quickly and 

 neatly, removes with a rasp, the overflow left on the casing at the 

 center of the tread by the twin tire mold. 



