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There are two distinct considerations
any fleet engineer should make, which
will make a critical difference. Firstly,
what payload do you expect to be
carrying and secondly, what is the
average speed of the vehicle? The
results from this simple research will
determine whether your vehicle will be
most affected by either momentum or
relative wind speed.
Let’s first address the subject of weight.
Most engineers will understand the
implications of momentum and inertia
when it comes to mass; and when
you’re talking HGV’s, you’re not talking
about a few hundred kilos. Make no
mistake, every time the driver puts his
right foot down on the accelerator of
a 44 tonne combination, overcoming
inertia will easily represent the largest
chunk of consumed fuel. Having
reached a comfortable cruising speed
with a healthy momentum, any braking
would subsequently burn all that stored
energy in wasted heat and the engine
has to start over again.
Weight therefore would seem an
important factor; yet the issue of weight
saving can be misunderstood. It is
possible to get a trailer tare weight down
to below 6 tonnes but this impressive
weight reduction, relative to the overall
total laden weight, is fairly small. As
an example, engineering one tonne of
weight out of your 44T tri-axle trailer
specification represents 2.3% of the total
mass. It doesn’t take a rocket scientist
to calculate that this reduction just isn’t
going to have much of an effect.
However, a 1 tonne tare weight
reduction may offer you a unique
opportunity to add more payload.
This won’t directly affect your overall
weight and fuel consumption, but it will
reduce the number of trips required
to transport the same load; indirectly
saving quite a high percentage in fuel.
On a smaller scale, you have to
consider the effect of a 500kg weight
saving achieved on a 7.5 tonne rigid.
When you understand that weight
is more critical when stopping and
starting, this relatively large weight
reduction will have a far greater effect
on fuel economy for a strictly urban
vehicle than any aerodynamic widget
you can stick on it.
Now we turn our attention to the
subject of aerodynamics. As your
vehicle approaches anything over
40mph, air resistance starts to become
a far more significant gas guzzler. In
fact, at 56mph, approximately half of
fuel burned is directly attributable to
aerodynamic drag.
As food for thought, an aerodynamic
trailer with a humble average fuel
saving of just 5% will save £1,466
per annum in diesel; a figure which
can’t be ignored. Under the same
circumstances, a Teardrop trailer with
the in-operation average fuel saving
of 11.3% will reduce fuel consumed by
over £3,000 per annum*.
These two key factors then should
drive the decisions you make about
how to reduce fuel consumption.
Trunking trailers that spend much
of their time running between 40
and 56mph will benefit hugely from
aerodynamic interventions whilst urban
trailers on strictly stop-start cycles
How to save fuel
weight vs aerodynamics?
The best of both worlds - Lafarge Teardrop
trailer engineered down to just 5,820kgs for
greater payload potential and incorporating
full-wrap side skirting and aerodynamic front
dome for optimum aerodynamic efficiency.
For commercial vehicles, the weight vs. aerodynamics debate
is always a subject worth tackling if you’re to secure the most
value from your fleet specification. Even at today’s lower diesel
prices, making the right call can generate significant savings in
fuel costs. We spoke to Don-Bur’s Richard Owens.
22
Logistics Business Magazine | February 2016
TRAILER ECONOMY