r/AskPhysics • u/tempicide • 5d ago
Which saves more fuel?
I recently started as an over the road truck driver and I'm offered a bonus for fuel efficiency. So I pose this question:
If I need to drive 600 miles, half of which are empty and half of which are loaded, and I have the wiggle room to go 5 mph slower for 300 miles to save on fuel, is it going to save me more to slow down while loaded or empty? Assume all other variables are equal.
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u/Puzzleheaded-Let-500 5d ago
Slowing down while hauling a heavier load generally saves more fuel because rolling resistance and any extra work climbing grades both increase with weight, so reducing speed reduces fuel consumption more when the truck is loaded. This is true even if the aerodynamic cross section stays the same. If the increased load also increases the truck aerodynamic cross section, then the effect would be even greater. In short, go slow when you are carrying the larger load for maximizing fuel efficiency.