OCR Text |
Show GOOD ROADS PNEUMATIC TIRES ARE BEST Off or Greatest Influence In Reducing Impact Force on Surface of Various Roads. (Prepared bjr the United States Department (of Agriculture.) Impnct tho forco resulting wben n truck wbeol strikes tlio surface of a road depends largely upon tho kind nnd condition of tho tire used on tho ! ivhecl, tho bureau of public roads of j tho United Statos Department of Agriculture Agri-culture reports nf tor a series of oxten slvo Investigations on tho subject. Wlion roada were built to carry tho trafllc of a few years ago tho actual weight or Bpced of tho load was only generally .considered. Much nttcntlon was paid to tho question of whether tho trafllc wns equipped with steel or -rubber tires, but n dcllnlto analysts of tho surface and supporting conditions of tho road and n determination of destructive forces were not deemed necessnry. Tho transition from horse-drawn horse-drawn to automobile and truck trafllc has chnnged tho surfaco nnd strength requirements of tho rond of to-day. When tho rcnlhatlon came that this heavy nnd sovcro trafllc was hero to stay and that roads would havo to bo built according to a very careful and thorough design In order to carry this trafllc It was found necessary to study very definitely all tho forces to which a road Is subjected. For two yenrs tho bureau of public roads has bcon working on tho problem of obtaining tho vnluo of tho Impact -forces on roads. Borne high points In their report recently re-cently mndo are: Thin or worn solid rubber tires, oven though they bo very wide, produce very high Impact forces. Pneumatic tires offer tho greatest Influenco In reducing Impnct forces, nnd with their uso tho Impnct Increases Only very slightly with tho speed of the truck. Cushion tiros, thnt is, tires having a dogroo of Boftncss nnd deflection between be-tween solids nnd pneumatics, offer corresponding cor-responding ndvnntngcs In reducing Impact. Im-pact. Impnct Increases with tho speed of Iho truck, but It cannot ho said to In- FT" "" l I Tif I luff HfeWCT i- ' .,, if. ,,., J - I Pneumatic Tlreo Reduce Impact on 8urfnce of Roads. crease according to any constant ratio or power of tho speed. Although heavy unsprung weight mny glvo hlghor Impnct than lighter unsprung weight, it cannot bo snld that this Is the major controlling factor. Tho relative destructive effect produced pro-duced by light-weight, high-speed trucks nnd henvy, slow-moving trucks has not been determined by these tests. Thoy do, however, Indicate thnt equal Impact may bo obtained under some conditions. Impact may bo ns high as seven times the stntlc load on ono rear wheel when n solld-tlro truck strikes n 1-Inch 1-Inch obstruction nt 10 miles per hour, nn nverngo vnluo being about four times. For pneumatic tiros tho mnxl-mum mnxl-mum Impact value Is probnbly not more than ono nnd three-fourths times tho lond at ono rear wheel, nnd nn nVerngu value Is not moro than one nnd one-fourth times the load. |