. Electric railway journal . ially improvesthe wheel performance, and at the same time reduces trainresistance. If one wheel is of a tape-size -J in. greater than its matethe result will be a slippage, when in service, of 6 ft. permile, and if each wheel is expected to give a performanceof 60,000 miles the slippage will be 360,000 ft. or approxi-mately 70 miles, providing the difference in diameterremains the same as when the wheel went into latter assumption, however, will not hold, for theslippage reduces the diameter of the smaller wheel so thatthe difference is continually gro
. Electric railway journal . ially improvesthe wheel performance, and at the same time reduces trainresistance. If one wheel is of a tape-size -J in. greater than its matethe result will be a slippage, when in service, of 6 ft. permile, and if each wheel is expected to give a performanceof 60,000 miles the slippage will be 360,000 ft. or approxi-mately 70 miles, providing the difference in diameterremains the same as when the wheel went into latter assumption, however, will not hold, for theslippage reduces the diameter of the smaller wheel so thatthe difference is continually growing greater, thereby hastening the time when the wheel must be removed fromservice on account of wear. Not only does slippage shorten the life of the wheel but,on account of the difference in diameter, the small wheelgrinds the rail and a sharp flange is the result. The con-tinual grinding against the rail also very materially in-creases train resistance, rail wear and the tendency forderailment on curves having worn TYPICAL SHELL-OUT IN WHEEL Extreme care must be used in mounting wheels to insureproper gaging. Not only must the distance from flange toflange be accurate, but the wheels must be uniformly spacedfrom the center of the axle. In pressing the wheel on theaxle recording gages should be used on the wheel pressto permit a study of the conditions of moimting on eachaxle. The pressure should increase uniformly from begin-ning to end. Another common defect in wheels is known as shell-out. Years ago it was supposed that shelling occurredon account of defects in the metal in the tread of thewheel; that possibly there was some foreign material, asslag or sand, imbedded in the metal which gave rise to thisdefect. It was found that the defect existed only in theclass of service having maximum amount of skidding andimder equipment of consider-able weight. It was also foundthat where a shelled spot oc-curred in one wheel the matewheel had a similar defect inthe same plan
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