The majority of the weight of a fully loaded HGV heading for Tesco will be the truck itself, I mean, what do forty pallets of crisps weigh? bread? teabags? There's loads of light goods that take up space but weigh next to nothing, yet it costs the same as a 250kg pallet of lager to get to the destination...what I'm saying here is that instead of thinking in terms of weight versus fuel savings, it's capacity, IE space
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.
Arfa
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.
When I shipped by worldly goods by sea, the charge was by the cubic meter.
Airfreight is by weight
But in the context of trucking a lot of things ARE heavy. Tins of this and that and most liquids are about a tonne a cubic meter.
Crisps are the exception not the rule.
And if you have ever driven a fully loaded commercial vehicle you will know that fuel consumption definitely increases.
Its less, but not swamped. I'd say a truck is probably at 56mph around
50/ 50 when loaded.
First find a motorway without any hills
Eddie Stobart gets paid the same whether the load is lager or crisps. Yes, it will cost him more to get the lager delivered than the crisps, but he does't charge any less when it's lighter loads like toilet rolls etc - it's one flat charge per delivery, so adding a few extra cubic metres which can be filled with light goods makes perfectly good financial sense.
In which case if you add a sixth to the load, the rolling resistance will rise by a sixth and the air resistance by SFA so you save 1/12th of the fuel. Worth doing.
Andy
Yes, but that wasn't the issue. The claim was that by using the larger trailers - significantly named "eco-trailers" - there would be less fuel used and hence less pollution, because it would result in less trucks being on the road. The point I was querying was if there was really a saving of one in six trucks, fuel usage / pollution wise, or whether the extra fuel that was going to be used to haul the bigger and heavier trailer, totally or partially negated the *apparent* fuel saving from taking one truck off the road, and distributing its load across six bigger ones. That was the implication, but I wasn't sure that it was strictly true, or at least quite as true as they would have you believe.
Arfa
Yes, that was my point exactly. I'm thinking that if you take a worst case example of a fully loaded truck, and then add to that a further fully loaded sixth of a truck plus the extra trailer hardware itself, is it going to use a sixth as much fuel again to haul that extra load ? Probably not quite, as a reasonably fixed part of the rolling load is the wind resistance of the trailer, which I guess will only be affected a small amount by the trailer being longer. But then again, maybe not. The front-face wind resistance won't change a lot, and I would guess that with the deflectors that all modern trucks have, that isn't actually all that high anyway, but the additional drag imposed by the vertical sides and roof of the extra 2 metres of trailer might in fact represent a considerable increase in drag, particularly given that these are curtain siders, with all the bobbles and protrusions that they entail.
Arfa
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-)
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