"Adrian" wrote in message
...
Nige Danton gurgled happily, sounding much like
they were saying:

within any given class are likely to be fairly similar. As a rough rule
of thumb, increasing drag starts to come seriously into play from about
60mph upwards.

Drag cubes with velocity and so it may become important at speeds lower
than 60 mph.

Trust me on this... I've got plenty of experience with low-powered,
unaerodynamic vehicles. It starts to come into play at about 60.

So why do large commercials use lots of fuel at a constant 30, more at a
constant 40 and even more at a constant 50?
If drag isn't the cause what is?