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This article was first published in 2008.
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In these days of high fuel prices and increased
concern about greenhouse gas emissions, lots of people want to know how the
weekly fuel bill can be reduced. Let’s take a look.
Driving Style
I bet more than half of you saw the sub-heading
‘driving style’ and wanted to skip straight past it. I am glad you didn’t.
Because of all the topics covered in this article, improving fuel economy by
altering driving style is the single easiest, cheapest and most effective
technique.
I once had a job photographing people in
restaurants. The pics would be taken then sold to the people as souvenirs of
their night out. I soon found that the job was a lot more about ‘sales’ than
‘photography’, so after a short time I gave it away. But the relevant part for
this story is that my boss, a woman in her mid-30s, often drove me from
restaurant to restaurant.
And her driving was a revelation.
She looked ahead literally only 20 or 30 metres;
every red light involved heavy braking – braking that was so strong that it
would have caused a skid had the road been wet. (I never rode with her when it
was raining – just as well.) When the traffic light went green, she just stomped
on the throttle and away we went.
The fuel consumption of that sort of driving is
just horrendous.
Even if you don’t drive as badly as she did, many
people could improve their fuel consumption (and decrease the consumption of
tyres and brakes) by driving better.
When a car is being driven for good fuel
consumption, the acceleration and braking are so smooth that a full glass of
water on the dash shouldn’t spill a drop. Think about that for a moment: it
means that when slowing for a red traffic light, the throttle lift-off should be
sufficiently far ahead of the light that the transition from throttle-on to
throttle-off to braking is one smooth continuum of deceleration. In fact, in
normal driving, if you need to swap your foot straight from the throttle to the
brake pedal, you’ve made a driving mistake.
When the light turns green, you should (in a
manual trans car) use plenty of throttle but change up early. It depends on the
car, but that might mean making your shifts at 2000 or even 1500 rpm. If you are
using a small throttle opening and changing-up at high revs, you’re wasting
fuel. In an automatic trans car, use whatever throttle behaviour keeps engine
revs as low as possible.
On the open road, acceleration and braking are not
the main driving style factors affecting fuel economy. Instead, the slower you
go, the better will be the fuel economy.
Now obviously common sense comes into play here –
no one is going to like you much if you drive down a 110 km/h speed limit dual
lane highway at 80. But as a specific example, a trip I commonly make is on a
4-lane each-way, 110 km/h freeway. If I am not in any hurry, I’ll sit in the
slow lane at 95 – 100 km/h.
Summary:
In urban driving you should drive smoothly and
look well ahead, predicting traffic behaviour rather than reacting to it. In
country road driving, travelling slower is the easiest way of improving fuel
economy.
Car Preparation
I know a bloke of the old school: he carries
around in his car’s boot a heavy tool box stuffed full of weighty bits. It’s
probably been in the boots of all his cars for the last 30 or 40 years: back
then, it was perhaps a necessity when travelling a long way in vehicles that
were not as reliable as today’s cars.
But such an unnecessary load simply wastes fuel.
Each time he accelerates, he’s also bringing up to speed a tool box that would
be better in his shed.
The same can be said of any extra load in your
car. If you drive primarily in urban areas, consider removing the spare wheel. I
reckon I’ve used my spare once in the last ten years; that’s been ten years of
carrying the thing around for very little use. (However, in small cars be aware
that the spare wheel may be part of the car’s crash safety strategy in a
rear-end collision.)
Heavy subwoofers are another weighty addition that
perhaps you can do without.
At highway speeds, aerodynamic drag uses the
majority of power being developed by the engine. Modern cars are vastly
slipperier than cars of yore; however, those advantages can be lost if the car
wears roof racks, is driven with the windows open, or someone has removed the
engine bay undertray eg to make oil changes easier.
Talking about oil changes, the thinnest oil
recommended by the manufacturer will reduce internal frictional drag. When it
comes time to replace the current tyres, consider fitting low rolling resistance
tyres. Tyre pressures should always be at the maximum end of the manufacturer’s
recommendations – however, I do not recommend some of the extremely high
pressures that people chasing fuel economy sometimes run. (I’ve seen suggestion
of pressures of 50 psi – the ride will be terrible, the handling suspect, and I
wonder if the insurance company would even cover you if you had an
accident.)
A fuel-efficient car should be well maintained:
the days of 10,000km “tune-ups” are long gone but by the same token, replacement
items like spark plugs, spark plug leads (if fitted), fuel filters and air
filters should be replaced at manufacturer-specified intervals. The EGR valve
and injectors should also be kept clean. We do not recommend fitting “upgraded”
aftermarket filters or sparkplugs; if the manufacturer’s original equipment
parts are too expensive, buy conventional replacement parts from a well
respected non-OE supplier.
Summary:
Keep the car as light as practicable and safe.
Make sure that its aerodynamic form is not degraded and keep the tyre pressures
at the upper limit of the manufacturer’s recommendation. Keep the car’s engine
well maintained.
Car Choice
‘Car choice’ – why is this being placed last?
Shouldn’t it be first? The reason we’ve put this at the end of the story is that
is usually what happens in real life – people try to improve the fuel economy of
the car they have, rather than having selected the car on the basis of fuel
economy.
Some things don’t change – and one of those is
this: A smaller engine car will give better fuel economy than a car with a
larger engine. Of course there are exceptions, but the general rule is very
broadly applicable. If you want lots of performance, pick a car that has a
turbocharger on that small engine. For reasons we’ve covered elsewhere (see Turbo'd for Fuel Economy), current turbo engines
tick all the right boxes – driveability, performance and fuel economy.
Reflect carefully on the criteria you want a car
to match. If you’re a performance enthusiast, think past the concept of
‘performance’ meaning only acceleration. Performance in terms of handling, in
brakes, in steering feel – none requires a thirsty engine.
If you take an annual holiday that goes off-road,
how do the figures calculate if rather than buying a 4WD, you hire such a car
for a week or two each year? (And keep in mind that you’ll also get a current
model each time!)
How many seats do you really need? What load space
versatility to you require? If you want a tow-bar, what is the maximum load you
frequently tow?
As an automotive journalist, I drive a lot of
different cars over the course of a year. But you probably don’t. Is it worth
spending $500 or $1000 to hire a range of different cars and then experience
them in your own driving environment, with your own requirements put into
effect? It probably is – and you’ll learn far more than on a dealer’s
drive-around-the-block with the salesperson twittering in your ear. Even if
you’re after a second-hand car that cannot be hired, sampling a selection of
current model hire cars of different types will at least open your eyes to what
actually works and doesn’t work for you, your family and your driving
circumstances.
Before we leave this topic, many people simply
don’t know what different cars are like. Some think that current turbo diesels
are slow and unresponsive – typically they’re not. Some think that hybrid cars
are incredibly gutless – usually they are not. Others think that large cars
always have lots of interior space – but many 4WD wagons have very poor space
utilisation. Make sure that you’ve experienced enough different types of cars to
make a meaningful car buying decision.
Summary:
Think outside of your preconceptions. Experience
what cars actually exist and what they do well and poorly. ‘Performance’ is a
lot more than just acceleration: with the exception of small engine turbocharged
cars, ‘acceleration performance’ invariably means higher fuel consumption.
Conclusion
We don’t think any of the points made in this
article are groundbreaking. Bluntly, they are not. But if you select the car
carefully on the basis of the real needs it must satisfy, keep it well
maintained and drive it well, you will be getting the best fuel economy possible
in your driving circumstances.
And that’s a pretty good thing...
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