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Show QUALITY OF ROAD MATERIALS Bureau of Public Roads Seeking Information Infor-mation of Especial .Value to Highway Engineers. Such Important questions as how hard a heavy motor truck pounds u Ia eimMit when going at o miles an hour and at lo miles an hour are being be-ing answered by investigators t'or the bureau of public roads, .United Sinus I lepartment of Agriculture, in a series of scientific experiments, which, wh.'ii ci'inpletcd, promise to be of great value val-ue to highway engineers. Already sufficient suf-ficient lesrs have been made t show that increased speed of a vehicle equipped- with hard rubber tires ire mendously increases the impact whicl its wheels .make on the roadway when there is any unevenness. On the olliei hand, where pneumatic tires are usei' increased speed adds comparatively Hi tie to the impact. It has hi--en sug gested that these tests wH! be o great value not only in settling qties tions of design but may also lead to ; 'rational basis for determining liceiHt fees for motor vehicles. Trucks have been used in thes. tests varying in size from a 1-ton true! up to a 7V-ton truck carrying an ex 1 cess load. Each truck was run over j, special recording device embedded in a roadway and the impact made by a 2-inch drop from a ledge built in the surface caused the deformation of specially spe-cially prepared copper cylinders forming form-ing part of the apparatus. The magnitude mag-nitude of the blow was accurately ascertained as-certained in pounds by measuring the extent, to which the cylinder had been forced out of shape. Kecent tests were made with a 3-ton 3-ton truck loaded with a -l-ton load so that the total weight on each rear w heel was 7.1XH) pounds, the unsprung portion (that not supported bv the springs) hemg l.TtX) pounds and the Army Truck Remodeled by the Post-office Post-office Department for Rural Service Pneumatic Tires Are Used. sprung portion (that portion supported by the springs) 5,300 pounds. The truck was equipped first will) an old solid tire that had been worn down to a thickness of 1 inch. Then, with exactly Hie'same load on the truck, a wheel was used fitted with a new tire 2y2 inches In thickness. And finally fin-ally the truck was equipped with pneumatic pneu-matic tires 42 by 9 Inches and blown up to a pressure of 142 pounds per square inch. The test demonstrated very clearly the bad effects r.n old tire is likely to have on a road sui-face and the greatly lessened Impact Im-pact produced by trucks when fhey are equipped with pneumatic tires. The tests show that as t lie vehicle's speed increased the Impact from the old hard rubber tire increased greatly. The impact from the new hard rubber tire was somewhat less. |