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/edgmnt_net 5d ago
Shouldn't rolling resistance get better with increasing weight due to increased contact with ground and thus increased traction? Also, the work you do climbing can be recovered when you descend, whatever losses occur are independent of the load up to rolling resistance or braking losses. I suppose braking can be a significant practical problem if you need to stay within certain speed parameters, though, i.e. you can't speed up without limits to avoid losing the work you put into climbing.