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|  MIL-T-62497
3.3 Performance.
3.3.1 Speeds and gradeability. High and low speed requirements shall be met with the
vehicle load to the specified GVW.
3.3.1.1 High speed gradeability. The vehicle shall be capable of ascending a 1.0 percent
grade at 50 miles per hour (mph). Gradeability shall be verified with calculations in accordance
with SAE J688 (see 6.3). Gradeability requirements shall be met with the main transmission in
direct drive.
3.3.1.2 Low speed. Low speed shall be calculated with the engine operating at not less
than 35 percent of recommended governed speed and shall provide a vehicle speed not greater
than 4 mph.
3.3.1.3 Maximum geared speed. The maximum geared speed at engine governed speed
shall be not less than 58 mph. Conformance to geared speed specified shall be determined by
calculating in accordance with the following formula:
Maximum geared speed (mph)=
Governed speed (rpm)
Total gear reduction x tire factor (see 6.3)
3.3.2 Service brakes. The service brakes shall control and hold the vehicle on a 30 percent
grade when the vehicle is loaded to its required GVW. The service brakes shall stop the vehicle,
loaded to required GVW, within the stopping distance requirements of Federal Motor Carrier
Safety Regulation 393.52.
3.4 Chassis components.
3.4.1 Engine. The engine furnished shall be the chassis manufacturer's standard or
optional engine for the commercial model truck which meets or exceeds the requirements of this
specification.
3.4.1.1 Diesel engine. The vehicle shall be equipped with a liquid cooled, compression
ignition, two-stroke or four-stroke cycle diesel engine, with not less than four cylinders. Engine
net horsepower used in performance prediction calculations shall be determined in accordance
with SAE JB16 or SAE J1349. A fan clutch shall be provided. The fan clutch shall reduce the
fan speed automatically when the fan is not required for cooling.
3.4.1.2 Oil filter. A full flow type oil filter shall be furnished.
3.4.1.3 Governor. An engine governor shall be furnished and set and sealed to limit the
maximum engine speed to the engine manufacturer's maximum recommended operating speed.
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