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|  MIL-T-62735
6.3 Performance prediction. SAE Truck Ability Prediction Procedure calculations and
calculations for low speed and maximum geared speed will be required by the contract. The
SAE Work Sheet Item 1 should include the chassis manufacturer's model number, engine model
number, drive axle(s) model number and gear ratio(s), tire size, and vehicle type, class and
model.
6.3.1 Conditions and factors used in calculations. Unless other conditions are cited in
the contract, calculations should be made for normal atmospheric pressure, normal ambient air
temperature, and still, dry air. The factors to be used in predicting truck ability (see 3.2.2) are
established as follows for the corresponding SAE Truck Ability Prediction Procedure Tables:
80 km/h (50 mph) performance requirements:
Table 1
- Tire Factor. This factor must relate to the size of
tires furnished by the contractor in accordance with
this specification.
Table 2
- Altitude Factor. 1.00
Table 3
- Rolling Factor. 1.613
Table 4
- Area Factor. For truck tractor, use factor 0.223;
for all other trucks, use factor 0.173.
Table 5
- Velocity Factor. 250.0
Table 6
- Altitude Factor. 1.00
Table 7
- Chassis Friction Horsepower. Use applicable power
unit GVW (to nearest, higher, 454 kg
(1,000 pounds)) and the engine speed (to nearest
100 rpm) which is required for 80 km/h (50 mph)
geared speed. For GVW and engine speed beyond
range of this table, factors shall be extrapolated.
Table 8
- Grade Factor. 0.75
Table 8A
- Correction Factor. Not required.
Table 9
- Road Factor. 0.0
69 km/h (43 mph) performance requirements:
Table 1
- Tire Factor. This factor must relate to the size of the
tires furnished by the contractor in accordance with
this specification.
Table 2
- Altitude Factor. 1.00
Table 3
- Rolling Factor. 1.315
Table 4
- Area Factor. For truck tractor, use factor 0.225;
for all other trucks, use factor 0.173.
Table 5
- Velocity Factor. 159.0
Table 6
- Altitude Factor. 1.00
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