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slowmover · 04-14-2014, 10:59 AM

Cummins White Paper (online; .pdf)

The power required to maintain a given road speed depends on the sum of the following forces:
 Aerodynamic Drag
 Grade Resistance
 Tire Rolling Resistance
 Engine Accessory/Drivetrain losses

To minimize drag resulting from crosswinds and turbulent air, tractor-trailer gaps should be minimized or aeroskirts should be used to smooth the airflow. Beyond approximately 30 inches, every 10-inch increase in tractor-trailer air gap increases aerodynamic drag by approximately 2%.

The effect of running all tires slightly underinflated (blue line on the chart) is significant. But all tires do not contribute equally. Notice that the trailer tires (green line on the chart) have a larger effect on fuel economy than either steer or drive tires.

tires that run hotter consume more fuel. A majority of this heat is generated by sidewall flex

 High average vehicle speeds with minimum time spent at maximum vehicle speed
 High percent trip distance in top gear (90+ % recommended)
 High percent distance in cruise control
 Minimum percent Idle/PTO operation
 Minimum service brake activity
 Number of Sudden Decelerations
 Service Brake Actuation's/1000 mi

Headwinds and crosswinds can significantly increase aerodynamic drag and reduce fuel efficiency. For every 10 mph of headwind or crosswind, mpg is reduced by nearly 13%. You cannot cheat increasing wind resistance

A TT is always trying to pass the TV. Nature of the beast, of this type of articulated rig. Things boil down to tires. If the load (pressure) is ideal, then much else is quite good, in short. But MUCH goes into ensuring maximum time at TT being aligned with TV. Not so easy (given resistance by RV'ers to sort and correct). Life is easiest on tires (for a given roadway) if mechanical and aero are best. And inputs by driver are short in time and distance to effect changes (and corrections are minimized to the point of nearly-not-existing by combined vehicle lash-up given best design/components). Make sense?

Trip sounds great, and FE looks good. That was an average speed given, correct? The number that matters is at trip end.

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04-14-2014, 10:59 AM	#15 (permalink)
slowmover Banned Join Date: Oct 2009 Location: Fort Worth, Texas Posts: 2,442 2004 CTD - '04 DODGE RAM 2500 SLT Team Cummins 90 day: 19.36 mpg (US) Thanks: 1,422 Thanked 737 Times in 557 Posts	Cummins White Paper (online; .pdf) The power required to maintain a given road speed depends on the sum of the following forces:  Aerodynamic Drag  Grade Resistance  Tire Rolling Resistance  Engine Accessory/Drivetrain losses To minimize drag resulting from crosswinds and turbulent air, tractor-trailer gaps should be minimized or aeroskirts should be used to smooth the airflow. Beyond approximately 30 inches, every 10-inch increase in tractor-trailer air gap increases aerodynamic drag by approximately 2%. The effect of running all tires slightly underinflated (blue line on the chart) is significant. But all tires do not contribute equally. Notice that the trailer tires (green line on the chart) have a larger effect on fuel economy than either steer or drive tires. tires that run hotter consume more fuel. A majority of this heat is generated by sidewall flex  High average vehicle speeds with minimum time spent at maximum vehicle speed  High percent trip distance in top gear (90+ % recommended)  High percent distance in cruise control  Minimum percent Idle/PTO operation  Minimum service brake activity  Number of Sudden Decelerations  Service Brake Actuation's/1000 mi Headwinds and crosswinds can significantly increase aerodynamic drag and reduce fuel efficiency. For every 10 mph of headwind or crosswind, mpg is reduced by nearly 13%. You cannot cheat increasing wind resistance A TT is always trying to pass the TV. Nature of the beast, of this type of articulated rig. Things boil down to tires. If the load (pressure) is ideal, then much else is quite good, in short. But MUCH goes into ensuring maximum time at TT being aligned with TV. Not so easy (given resistance by RV'ers to sort and correct). Life is easiest on tires (for a given roadway) if mechanical and aero are best. And inputs by driver are short in time and distance to effect changes (and corrections are minimized to the point of nearly-not-existing by combined vehicle lash-up given best design/components). Make sense? Trip sounds great, and FE looks good. That was an average speed given, correct? The number that matters is at trip end. .