Brake Tests

296 mean coefficient of friction higher than with sohd shoes. (Par. 541-A.) (n) The superior durability of the plain slotted shoe as compared with the plain solid amounts to 11.7 per cent, under single-shoe brake conditions and 5.9 per cent, under clasp-brake conditions. (Par. 543-A.) (o) The shifting of the bearing area will tend to be more rapid if the size provides more available area for shoe bearing. (Par. 514-C.) (p) Flanged shoes provide more available area for bearing than unflanged shoes. (Page 240.) (q) The shortest stops in the entire series of road and laboratory tests were made with flanged brake shoes and without undue wheel sliding. Their use in road tests shortened the stop approximately 12 per cent., and in the laboratory 30 per cent., as compared with the best similar tests in which unflanged shoes were used under similar conditions. (Par. 450.) (Fig. 97.) (r) The wear of the flanged solid shoes per unit of work done is 19 per cent, less than for plain solid shoes, and for flanged slotted 26 per cent, less than for plain slotted shoes, or 30 per cent, less than plain solid shoes. (Par. 545-B.) (s) The wear of plain slotted shoes per unit of work done is 5 per cent, less than the wear of plain solid shoes, and the wear of the flanged slotted is 13 per cent, less than tlie wear of flanged solid shoes. (Par. 545-C.) (t) For the same amount of work done flanged solid cost 16 per cent, less than plain solid shoes, and flanged slotted cost 23 per cent, less than plain slotted, or 27 per cent, less than plain solid shoes. (Par. 545-D.) (u) Approximately 136 per cent, more stops will be required to wear out the flanged solid than will be required to wear out the plain solid shoe; 158 per cent, more stops to wear out the flanged slotted than the plain slotted shoe, and 171 per cent, more stops to wear out the flanged slotted than the plain solid shoe. (Par. 545-E.) (v) Shoes of the same type and.hardness liad a high rate of wear per unit of energy absorbed when a low coefficient of friction was developed and, conversely, a lower rate of wear when a higher coefficient of friction was developed. (Par. 514-B.) (w) Under clasp brake conditions with cast-iron brake shoes the indications are that the mean coefficient of friction is a maximum and the shoe wear a minimum when the Brinell hardness of the cast iron is about 190. (Par. 546.)