Re: Traveling with a lighter load
Reply #3 –
Weight is a significant factor in MPG on mountains.
Virtually insignificant on flat ground.
Said another way, the HP demand on a grade is very dependent on weight.
HP demand on flat ground is very dependent on aerodynamic drag, with weight being a lot less of a factor.
Examples (from a Caterpillar Corp document, but applies to all heavy vehicles-- physics is physics). All HP requirements are HP at the rear wheels:
Flat ground, 55 MPH:
34,000 GCW coach103 HP
40,000 GCW coach 110 HP (only 7 HP more than lighter coach)
On 6% grade 55 MPH:
34,000 GCW coach 402 HP
40,000 GCW coach 462 HP (60 more HP than lighter coach)