OCR Text |
Show STUDY OF WEIR OF 110. TIRES Tests Being Made to Determine Deter-mine Wear on Tread by Road Surfaces. A study of the wear of automobile tires has been made to determine, ns far as possible, the destructive effect of different types of road surfaces on the tread rubber, so that, insofar as possible, surfaces may be so improved im-proved as to make the total cost of building and maintaining road surfaces sur-faces and of operating the traffic over them a minimum, according to Charles M. Hayes, president of the Chicago Motor club. The cost of tires is one element of the cost of operating operat-ing motor vehicles and may well be studied. The University of Kansas, co-operating with the United States bureau of public roads and the State College of Washington, has conducted a series of tests in an effort to determine the loss of tread rubber caused by several sev-eral types of road surfaces, including concrete, brick and bitulithic pavements, pave-ments, penetration, macadam, and several sev-eral types of gravel and broken stone. The following tentative conclusions have been drawn from the few data now available : Tentative Conclusions. 1. Tire wear increases with the speed. 2. Tire wear increases with the temperature. tem-perature. High temperatures are very destructive to tires. 3. The wear of rear tires is greater than that of front tires, the relative wear of rear tires being 200 per cent on smooth pavements, and as little as 18 per cent on grave) surfaces, probably prob-ably averaging 150 per cent of the wear on front tires. 4. Tire we;: per ton of car is prob ably constant for any given road surface, sur-face, when size of tire, load and inflation in-flation pressure are determined by a single standard. 5. A few records of bus companies show actual tire mileage life on different dif-ferent road surfaces in approximate Agreement with tire wear tests on similar surfaces. Relative Tire Wear. 6. Relative lire wear index numbers, num-bers, based upon average concrete pavements as 1.0 are approximately 2.0 for pood gravel and macadam, 4.0 end 5.0 for average western macadam or crushed chert gravels, and may be as high as 10 or 11 for unusually unfavorable un-favorable surfaces. Based upon lire wear alone, average size cord tires should show a life of 20.000 to 24.000 miles upon pavements; 10.000 to 12,-000 12,-000 miles on good gravel or mac odam, and as little as 2.000 to 4.000 miles upon unfavorable surfaces. The corresponding costs per vehicle mile are about 0.5 cents for pavements, 1.0 cents for average gravel or best macadam, 2.3 cents for average macadam, and maybe as much ns 5 cents per vehicle upon road surfaced of loose, sharp-edged sioncs. |