On Fri, 26 Oct 2012 11:46:05 +0100, The Other Mike wrote:

The weight is rather less important than you might think. Consider a
truck going a constant speed down a motorway for ages - where are the
losses? Weight is important for acceleration, but once you're at a
constant speed none of that is going on.

First find a motorway without any hills

On average you stay at the same height, yes you'll burn more fuel going
up hill but then you go back down. Modern engines don't burn fuel under
engine braking...

Not sure if I posted a link to a .pdf I found the other day in relation
to this thread. That said each extra tonne of payload added 0.112 mpg. If
I didn't post a link I bet I can't find it again. B-)

--
Cheers
Dave.