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How to get an extra 20 miles per tankful free!
If you are a fairly typical driver, a change to your driving style can give you a 10% improvement in fuel consumption. For a car with a typical range of 300 miles, this represents an extra 30 miles of motoring on the same fuel; not to be sneezed at with current fuel prices!
One often reads, in the motoring press, that official fuel consumption figures are misleading, because ‘no-one gets anywhere near those figures!’ Well, I have always bettered the official figures, and have done so in a variety of vehicles, and I would like to help you do the same.
Drive Smoothly
The overriding ingredient in improving your driving style to gain those extra miles is improving the smoothness of your driving.
Smoothness is the hallmark of a good driver, and to drive smoothly requires good anticipation of what is happening on the road up ahead, so that you can, for example, lose a little speed early, rather than braking later and more harshly and thereby losing a lot of speed, which, of course, requires more fuel to make up the speed afterwards.
To give an extreme example in order to make this point, assume you are on a 30mph road, with a parked car some distance ahead on your side of the road, with a vehicle coming towards you on the other side of the road.
If, initially, you thought you could get through first, and then realised at a late stage that you could not, you would, at that point, be forced to brake virtually to a halt to let the other car through first. A lot of fuel would then be needed to get your car back up to 30mph.
If, instead, you had realised 100 yards away that both cars would reach the obstruction at the same time, you could have simply come off the accelerator to lose just a couple of miles an hour. The opposing car would then have reached the obstruction well before you, and would have passed it by the time you reached the obstruction. Indeed, if you had had superhuman judgement, and could have realised one mile before the obstruction that you would need to slow slightly, you might have needed a mere 1/2 a mile per hour drop in speed to achieve the desired result.
No-one, of course, is that good, but taking a problem to an extreme can often lead to a clearer understanding of the problem.
And, in attempting to drive more smoothly, avoiding unnecessary changes of speed, you will also be safer, because you wont make the sudden changes of speed or direction that take other drivers by surprise.
Smooth driving also reduces the chance of a skid, by building the braking, accelerating, or cornering loads on the tyres steadily, rather than abruptly, thereby minimising the risk of breaking adhesion with the road.
In Grand Prix Motor Racing, Alain Prost, nicknamed ‘The Professor’, drove so smoothly he made it look easy and unspectacular, but, by using the tyres up to but not beyond their limits of adhesion, he could get the most out of the car. Not for him the lurid slides and twitching steering wheel! Smooth does not necessarily mean slow! It means efficient!
Jenson Button is this era’s ‘mister smooth’, and whenever it rains during a race, he is usually the fastest driver on the track. When Honda give him a good car, he will, in my view, be able to give Lewis Hamilton a run for his money.
Needless to say, smooth driving on your part will also be appreciated by your passengers, as well as by the mechanism of your car.
Leave a good gap to the vehicle in front
It is far easier to smooth out your speed variations if you leave a good gap to the previous vehicle. If you drive too closely, you have no option but to brake when the other driver does and accelerate when the other driver does. By driving with a bigger gap, you will be able to smooth out at least some of the other driver’s erratic speed changes. Accelerating a car, especially a heavy one, requires extra fuel use, so try to maintain a steady speed.
Have you noticed how, when traffic slows on a motorway, it is the outer lane that slows first and with the greatest speed change, whilst the inner (slow) lane typically slows less abruptly and with far less speed change?
This is because the fastest lane, which should, on safety grounds, manifest the greatest inter-vehicle gaps, is usually the lane in which vehicles are travelling most closely, whilst the inner lane, by being less congested, has larger gaps and, consequently, greater elasticity.
Again, it is instructive to take the argument to an extreme. Imagine a line of vehicles literally nose to tail, with no gaps at all, and this line is 20 miles long. What happens when the leading vehicle, 20 miles up the road, stops? Well, of course, the last vehicle in the 20 mile crocodile has to stop too. There is no elasticity in the system to allow for following vehicles to do anything other than mirror immediately the speed changes of the lead vehicle.
Leave a good gap, so as not to be a slave to other drivers’ speed variations!
Don’t drive faster than is sensible
Obviously, the faster you drive, the greater will be the work your engine has to do to overcome air resistance, which is the dominant component of resistance to motion at typical main road speeds. Because the aerodynamic drag increases as the square of the speed, the power requirement increases as the cube of the speed, so a small increase in speed can result in a big increase in the amount of fuel used.
If you try to maintain a steady speed, you will reap substantial benefits in fuel consumption. If you accelerate to pass a slower vehicle, then have to slow down until a suitable opportunity arises to pass the next, and so on for many miles, you can find your journey shortened by only a few minutes, yet you will have used far more fuel than if you had simply accepted trundling along at the same speed as the bulk of the traffic. A cost-benefit analysis would show that the time saved was simply not worth the extra fuel used and the additional exposure to danger involved.
And, in addition to saving fuel, a less press-on style of driving will scare far fewer oncoming motorists, as well as your passengers.
Use of Gears
It often helps to change up early, provided you don’t cause the engine to labour.
A petrol or diesel engine usually produces its power most efficiently at the engine speed corresponding to the peak of the torque curve. Screaming the engine will produce more power, with more bangs per second, but that power will be produced less efficiently, with greater mechanical friction and airflow losses within the engine, so, find where your car’s engine torque curve peaks, and change up appropriately.
Other considerations
The foregoing has concentrated on driving style, as a means of improving fuel consumption, but, as technology improves, cars are becoming ever more economical, so, if you are thinking of changing your car, here are some things to consider.
- If your journeys are short, or involve a lot of stop/start driving, have a look at cars that are small and light. Stopping and starting a heavy car is obviously going to use a lot of fuel. Warming up a cold engine takes more fuel with a big engine than with a small one, too, and, if your car has a fuel consumption readout, you can easily see how much more fuel is used in the ‘warm-up’ phase.
- Conversely, if your journeys involve lots of main roads, look for cars that are aerodynamically good. Not only do they need to have a low drag shape, but they also need to have not too large a frontal area. Most tall 4x4s are disastrous in this respect, having not only large frontal areas, but also having a bluff shape, splashing their way through the air rather than slipping through it unobtrusively. If you need 4 wheel drive, but make lots of main road journeys, cars like the Subaru Legacy make a lot of sense. The Legacy is not, in absolute terms, a ‘low fuel consumption car’, but a diesel version (which has received glowing reviews in the motoring press) is currently in dealerships as a demonstrator, and it presents a welcome alternative to the Audi Quattro as a comfortable 4WD long distance cruiser.
- If you need four wheel drive to ensure traction on steep muddy slopes, but make many short journeys, the FIAT Panda is available in a 4WD version.
Economical small cars
The Table in the previous section, produced partly from the Government’s web-site on fuel consumption and emissions, is a guide towards choosing your next ‘runabout’.
Small cars are often fun to drive, and some have become surprisingly refined.
Since so many short journeys have just the driver on board, it makes sense to keep larger vehicles for longer journeys, when a full passenger load is more likely, and with rising fuel prices, save your pocket as well as the planet!
Do insist on a decent test drive before choosing your next car. Cars may well begin to look alike, but the way they feel can be quite different, as some manufacturers might concentrate on, say, comfort at the expense of sharp reflexes, whilst others produce a ‘driver’s car’, with responsive and friction free steering, but placing less emphasis on passenger space or comfort. You can only assess such qualities with a test drive. Only you know what feels right for you, however much the motoring press might rave about certain aspects of a car’s behaviour!
Long journeys require low noise levels, good ventilation, and comfortable supportive seats.
We intend doing our own road tests on the more promising small cars in the future, and leave the rest of the motoring press to the Mercs and Ferraris!
Green Car Show
A green car show was held as part of the Eden Project, from 23rd to 31st May. For details, go to http://sgcs.edenproject.com/?dm_i=278129943. Axon Automotive showed their 80+ mpg vehicle, whilst other manufacturers showed their economical/greener cars.
I was unfortunately unable to attend the Show, but especially wanted to take a look at the Axon Automotive vehicle.
They are happy for us to provide a link to their web-site, which can be found at www.axonautomotive.com and, for the time being, this will have to suffice until I can visit them and provide you with a more in depth article.
It is claimed that 100mpg is feasible, which is a magnificent achievement if it can be obtained under practical give-and-take driving conditions, so I am very much looking forward to taking it for a test drive in the near future.
Rod Kirkby
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