On 26/10/2012 01:25, Arfa Daily wrote:

I would dispute that it costs the same to haul 50 cubic feet of crisps,
as it does to haul 50 cubic feet of cans of lager. The weight of the
goods being hauled is a significant part of the overall equation, as is
the weight of the trailer. Another two metres of that, plus the
additional axle and the equipment to make the rear axles steerable, is
not going to be insignificant, and when you add in the (potential)
weight of the extra goods - probably somewhere in the region of 500
cubic feet in the additional capacity afforded by this trailer - the
overall weight of the trailer will be a fair percentage higher than that
of a 'standard' trailer. The energy to move this, and keep it moving,
comes from the tractor unit's engine, and the energy to make this
happen, is derived from the diesel that it burns. If the engine has to
output more power to haul the extra weight, then it must use more
diesel. I was just interested in how much more diesel, as this obviously
at least partially negates any claims of using less diesel and producing
less pollution than having an additional sixth of a conventional trailer
on the road.

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.

The vast majority is air resistance, and that's not going to be much
more at all for the bigger trailer - same frontal area, no massive
difference in shape.

There will be some rolling resistance, and a part of that will be
proportional to weight, but it'll be swamped by air resistance.