Caterpillar Performance Handbook, January 2017, SEBD0351-47

Engine Selection

On-Highway Trucks

Step 2A: (Manual and Automated Manual Transmis- sions) Verify the Engine selected in Step 1 can get the Truck moving on the customer’s maxi- mum grade. Startability: Is the ability of the truck to start moving on

Step 2B: (CX31 Automatic Transmission) Verify the Engine selected in Step 1 can get the Truck mov- ing on the customer’s maximum grade. Startability: Is the ability of the truck to Start moving on the steepest grade the driver will face. For an Automatic Transmission a simple equa- tion cannot be used to predict Startability. For the CX31, see the Startability chart in Appendix G. It assumes starting on the best concrete. To more accurately predict Startability, ground conditions must be considered. Subtract the effects of ground conditions from (S) to determine the Max- imum Predicted Startability. S = See Appendix G Ground Conditions: See Tire Pavement Factors table or Subtract 6% for every inch of tire penetration. Maximum Predicted Startability = S – Ground Conditions Startability must be equal to or greater than the cus- tomer’s maximum percent grade. If below Maximum, Select an Engine with equal or greater HP and Higher Fully Developed Torque from Engine Specifications table. Rerun the Startability calculations to verify.

the steepest grade the driver will face. The equation below (S) calculates the Theoret- ical Maximum Percent grade for the Engine you selected in Step 1. To more accurately predict Startability, ground conditions must be considered. Subtract the effects of ground conditions from (S) to determine the Maxi- mum Predicted Startability.

S = (Tc × R × M) (10.7 × GW) Tc = Fully Developed Torque (from Engine selected in Step 1). See Engine Specification table. R = The overall Driveline gear ratio. Transmission (low gear) × Axle × Aux Trans ×Drop box Omit Aux Trans and Drop Box ratios if not used M = Tire Revolutions per mile. See Appendix I. GW = Desired Gross Vehicle Weight or Gross Combi- nation Weight. 10.7 = Constant. Ground Conditions: See Tire Pavement Factors table or Subtract 6% for every inch of tire penetration. Maximum Predicted Startability = S – Ground Conditions Startability must be equal to or greater than the cus- tomer’s maximum percent grade. If below Maximum, Select an Engine of equal or greater HP with Higher Fully Developed Torque from Engine Specifications table. Rerun the Startability calculations to verify. Continue to Step 3 for final Engine selection.

Step 3: Final Engine Selection. In Steps 1 and 2 you selected an Engine that had enough HP to main- tain cruise speed and start on the maximum grade. Before making the final Engine selection, factor in application and driver habits. For example, additional Torque may be required in mountain- ous regions. Perhaps a smaller Engine can be used to save fuel if the driveline gearing is modified.

12-22 Edition 47