People are often surprised – and in some cases can become quite grumpy – when they find they are unable to match the official fuel economy figures for their cars. There seems to be an assumption that if the official figure is, say 54mpg, that’s what the car should be doing all the time.
This is unrealistic. A car’s quoted economy shows how much fuel it uses on a specific test. On a different route it will almost certainly produce a different result.
There are many factors to consider, including road, weather and traffic conditions. There’s not much you can do about these things, but you can do a lot about your driving. With a bit of care, not only can you match the official figure, you may even be able to beat it by 20% or more, substantially reducing your fuel bill in the process.
Of course, there are compromises. Driving economically means driving slowly, and there will be times when you don’t want to do that. You also need to keep yourself and other road users safe, and preferably avoid annoying other drivers.
With that in mind, here are some things to consider if you want to delay your next visit to a petrol or diesel pump.
Accelerating hard is great fun, if you like that sort of thing, but it uses a lot of fuel. From a standing start, how quickly do you really need to get up to 30mph in town? Almost certainly not as quickly as the car is capable of. A very light application of power is all you really need, especially if there’s no one immediately behind you.
Similarly, you don’t need to get from 30 to 60 straight away as soon as you head into the country. A gentle increase in speed will do the job. If the driver behind is impatient and wants to get past, let them get on with it.
Obviously you should get up to motorway speed fairly rapidly as you’re entering from a slip road, but even then you can use the whole of that road to get up to 70mph, or whichever speed you have chosen, rather than do it in the first few yards.
Yes, sometimes you have to brake. No argument there. On occasions, though, it’s worth asking yourself why you needed to.
On a country road, you might have had to slow down slightly for a corner – in which case, if you know the road well, why did you use fuel a few yards ago accelerating to a speed you can’t sustain now?
This is all about thinking ahead. It also applies when you can see that you’re going to have to stop shortly because of a traffic queue or some other obstruction. Rather than keep the power on until you absolutely need to slow down, you can save fuel by backing off and letting the speed fall gradually.
If you do this and find that you need the brakes only to wipe off the last few mph, you know you’ve timed it right. It becomes very easy with only a little practice.
Out of town, what a car is fighting against more than anything else is wind resistance. This increases dramatically as speeds rise, so you need a lot more power – and therefore fuel – to drive at 60mph than 50, and much more again to maintain a steady 70.
On a long motorway run, you can save a remarkable amount of fuel if you’re not in a hurry, but it’s best to avoid cruising in the mid 50s mph as that’s what all the HGVs will be doing, and you don’t want to get tangled up with them.
At a steady 50, they will all pass you, and you’ll use a remarkably small amount of fuel. At 60, you’ll pass them, and you’ll still notice the improvement in fuel consumption.
Really serious economy drivers will stick to 40, but at that speed driving from London to Leeds will feel like you’re crossing the whole of Asia.
When trying to save fuel it seems obvious that you should back off when going downhill. Your trip computer will tell you that this gives incredible instantaneous results, but it’s not helpful for the journey as a whole.
In fact, it’s better to accelerate gently to above your intended speed on the downhill bits. If the road goes uphill again immediately afterwards, you can use that section to get back to this speed. This is much more effective than crawling downhill and having to power your way up again.
If the next section is flat, even better. Accelerating downhill will mean you hardly have to use any power at all for many yards on the level piece of road.
Checking your revcounter
Unless you are competing in motorsport, your car’s revcounter isn’t normally a useful instrument, but it can be a big help when you’re trying to drive economically.
Most modern engines (especially diesels, though it applies to many petrol ones too) can operate perfectly well between 1500 and 2000rpm on level or downhill stretches of road.
The lower figure varies from car to car. You’ll soon find what it is if you have a gearshift indicator (as most cars do nowadays) because it will suggest a downchange as soon as you let the revs drop too low.
Smoothness is important in all types of driving. When economy is the priority, unhurried gearchanges and gentle applications of power will reduce fuel consumption, and won’t reduce your journey time noticeably.
Smooth steering has its benefits too. If you gently turn the wheel to the point where you have just enough steering, you’ll avoid tyre scrub which would slow the car down unnecessarily and leave you having to use more fuel to get back up to speed.
This is one of the few cases where the driving techniques for racing and economy are very similar.
If you’re maintaining a certain speed – say 40mph – on a flat piece of road, it’s helpful to ease off the power every so often (you won’t be using much anyway), let the car ease down to 38mph and then apply power again to bring it back up to 40.
Adding periods of acceleration may seem counter-intuitive, but the overall effect on economy is positive. The first time I heard about this I was very sceptical, but I’ve found that it works.
With a little practice you can easily get to the point where your passengers won’t realise you’re doing it. Nor will they notice the few seconds that have been added to the journey time.
Switching things off
Unless there’s a separate power source for them, electrical systems give the engine more work to do and make it use more fuel.
The amount varies. The radio won’t make much difference, but the headlights will. There’s not much you can do about this. If you need to have the headlights on, you need to have them on, and that’s all there is to it.
Air-conditioning is different. It consumes so much power that you can actually feel a less powerful car slow down when you switch it on.
It has its benefits, of course, but you don’t need it to be on all the time. When the car’s windows are clear and the air quality is good, switch it off for a while and watch your fuel economy improve.
Start-stop systems can usually be switched off, and when they were introduced some people did just that. I could never understand why. Perhaps they thought they were the work of the devil.
They are actually very useful. What’s the point of having the engine running when the car is at a standstill? You are literally using fuel for no reason. Assuming the system is reliable, the engine will fire up again as soon as you need it to, though it’s worth checking exactly how this happens on your particular car so you don’t become stranded for a brief but embarrassing period.
To answer a frequently asked question, yes, restarting the engine uses quite a lot of fuel, but only about as much as it would have used anyway if it had been idling for three seconds. If you’ve been stationary for longer than that, you win!
(Full disclosure: I have occasionally disabled start-stop systems, but only ever in a motorsport context, when fuel economy wasn’t exactly a priority.)
What not to do
Never coast along with the gearbox in neutral. If an emergency develops you’ll spend what could be a critical second or two selecting a gear.
Besides, it won’t help your economy. The fuel supply to modern engines is cut, on appropriate occasions, when a moving car is in gear, but not when it’s in neutral.
Even more importantly, never EVER switch off the engine while you’re moving. Sure, you’ll save fuel. You’ll also cancel all the power assistance systems, so the brakes and steering will become unbearably heavy, and sooner or later the steering will lock, with appalling consequences.
Don’t try to gain an aerodynamic advantage by driving within a few inches of the vehicle in front. This does actually work, especially if you’re following a big lorry, but it carries an enormous risk.
The chances of becoming involved in a crash are very high. If that happens, the cost of repairing or replacing your car will dwarf the amount you saved on fuel, assuming you get out alive at all.