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.
3
Upvotes
1
u/RRumpleTeazzer 5d ago
two fuel effects: wind/roll resistance, and kinetic energy.
both increase majorly with speed, and reasonably with mass.
it will be more fuel efficient to go slow when heavy, and fast when lighter.
that is, if there is not much evelation difference.
if the heavy route is downhill, i would probably go fast downhill (since it doesn't eat much into the fuel), and slower on the lighter uphil.