Caterpillar Performance Handbook, January 2017, SEBD0351-47

Engine Selection

On-Highway Trucks

Step 1 Calculations : Addup theHP required at the expected vehicle cruise speed. NOTE: All the following formulas can be programmed into a Spread Sheet for faster evaluation. Rolling Resistance: The HP required on a flat surface

ENGINE SELECTION There are many factors that dictate the correct engine size for a specific application. It’s possible to use a mathematical approach to add up all the horsepower demands to size the engine. However, it’s also impor- tant to understand the application and driver habits. In addition, understand how the customer’s other trucks are configured. This critical customer knowledge is used to verify or modify the results of the mathematical approach to achieve the best engine selection for the application. Mathematical Approach Overview: 3 step process. 1) Add up all the HP loads at vehicle cruise speed. Examples of HP demands are: Rolling Resistance, Drag, Slopes, Road Surface, Driveline Losses, Accessories, and Power Takeoffs. 2) Determine the Torque required to start fully loaded on the customer’s maximum grade. This is called (Startability). 3) Use your knowledge of the application to verify if the Engine selected in steps 1 and 2 makes sense.

to overcome Tire Squat. Since tires are not perfectly round, (especially when loaded) the Truck is climbing a small slope just to move forward.

(6.1 + (0.06 × MPH)) × Cp × GW × MPH 375,000

Pr =

Cp = Tire Pavement Factors. See table below. GW = Gross Vehicle Weight or Gross Combination Weight required for the application. 6.1 = Constant. 0.06 = Constant. 375,000 = Constant. MPH = Desired Cruise Speed (not maximum speed).

Tire Pavement Factors Surface

Bias 1.00 1.20 1.50 1.75 2.00 7.50

Radial

LP Radial

Wide Base

Concrete

0.70 0.85 0.90 1.00 1.20 1.70

0.63 0.70 0.83 0.98 1.13 1.63

0.50 0.60 0.70 0.85 1.00 1.50

Cold Blacktop Hot Blacktop

Hard Soil

12

Hard Gravel Loose Gravel

Sand

12.00

Edition 47 12-19