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42 Table 4-6. Features to be included in maintenance manuals. Parameter Tolerance Cross reference Difference in wheel diameter between Within 1/16 inch (1.6mm) Section 3.6.1 wheels on the truck Wheel wear on tread before scrapping Depends on wheel and rail profiles Wheel wear on flange before scrapping Depends on wheel and rail profiles Wheel gauge +0.04 inches (+1 mm) Wheel taper +0.5o Flange height Minimum 0.75 inches (18 mm) Section 3.6.2 Flange angle +3o, -2o Section 3.6.2 Wheel back-to-back dimension +0.04 inches (+1mm) Axle parallelism 0.6 mm (0.025 inches) Section 3.6.1 4.6.4 Maintenance Tolerances 4.8 Future Vehicle Design Vehicles are designed to manufacturing tolerances but may This chapter can also be used as guidance on the overall design be maintained to different tolerances. Also, dimensions will of LFLRV most likely to give trouble-free performance on U.S. be allowed to vary within operating tolerances before main- and Canadian transit systems. This assumes that the design is tenance or corrective action occurs. limited to the scope of the research (i.e., LFLRVs having an The maintenance manuals should include tolerances for all unpowered center truck with IRWs), but it needs to be re- the features shown in Table 4-6 that are associated with the emphasized that other types of LFLRV may also be a possibility. performance of the center trucks on LFLRVs; these are The guidance will apply to the two "long-term" situations derived from the standards mentioned in Section 4.4, or are D and E of Table 4-1 (Table 4-7). In these cases, the guidance typical of tolerances in use in the industry. They are not shown in Table 4-5 will apply, but it is possible to identify a exhaustive. Where actual tolerances are shown, these will only standard set of parameters that may well have a ready market, apply for vehicles that also conform to the recommendations especially for Situation E, that would have the following fea- for new systems specified in Section 4.4. In all other cases, tol- tures. Option A is suitable where flange tip running exists on erances must be developed based on the principles outlined most switches and crossings on the system and Option B in this guidance and described elsewhere in the report. where it does not. The suggested parameters are Avoid creating rough wheel surfaces because of wheel truing--rough wheel surfaces increase derailment risks, Floor height: 350 mm (133/4 inches) especially on LFLRV center trucks. A surface finish of N8 Center truck wheel (125 inch) should be achieved. diameter: 660 mm (26 inches) Center truck wheelbase: 1800 mm (5 feet 11 inches) Wheel gauge: 1,426 mm (56.14 inches) 4.7 Vehicle Modification Wheel width: Option A 4 inches (102 mm) Option B 5.25 inches (133 mm) Circumstances can arise where either the supplier or the Wheel taper: Variable taper. transit system undertakes modifications to vehicles. Where Wheel flange height: Option A 22 mm (0.87 inches) vehicles are transferred between systems, it may be necessary Option B 20 mm (0.79 inches) to make modifications because of different track geometry or Flange angle: Variable between 72o and 75o other reasons. In all these cases the modification must be seen as a design change and both the modification itself and any Back-to-back wheel other features of the vehicle that may be altered as a result dimension: Depends on flange thickness must go through the same processes as would be associated with a new design, including These key critical interface parameters are associated with center truck design based on the research carried out and Application of the fundamental guidance Guidelines 1 and 2 assume that the equivalent infrastructure standards also apply. (see Section 4.3); Application of the proposed specifications (see Section Table 4-7. Situations where future vehicle design 4.4); will apply. Acceptance process (see Section 4.5); and Ref Situation covered Revised maintenance standards with new manuals, train- D Existing system, replacing vehicles with ones to a new design ing and tolerances (see Section 4.6). E New system with new designs of vehicle