James Stanford illustrates how driving style can have a dramatic influence on fuel consumption
Two components largely determine a car’s fuel consumption – the human brain and the right foot. Automotive engineers might strive to make powertrains as lean as possible with a raft of cutting-edge technology, but it is the nut behind the wheel who really dictates how much fuel is used.
To prove it, Australian Business Auto has hit the road in a base model FG Ford Falcon to measure the difference driving attitude can make. The attitude test is carried out over a 120km loop, comprising a mixture of city and country roads. I will complete one lap of this circuit driving smoothly with fuel consumption in mind. Common sense will be thrown out the window for the second lap as I drive like someone in a real hurry.
The first lap is eminently more enjoyable in a laid-back way. I manage to keep up with the traffic, but I feed on the power carefully. Trying to keep momentum is the key and I avoid any unnecessary braking and accelerating. To try to save a few extra millilitres of fuel, I turn the air-conditioning off. The Falcon has a five-speed automatic transmission, so I let the gearbox do the work, rather than flicking it into the manual Tiptronic mode.
This route contains some steep hills, suburban traffic, speed humps, a highway stretch and a fun, twisty run, so I’m naturally surprised when I refill the tank and check how much dino-juice was used. A quick calculation reveals the Falcon has used 9.84 litres for the 120km, and the trip computer backs up the reading. This is an impressive number for a six-cylinder family car with 195kW that weighs
a considerable 1700kg.
For the next test, I put my cap on backwards and drive like someone else is paying for the fuel. It’s all legal, with no speeding or wheelspinning, but I do accelerate quite hard and brake with equal gusto. I change gears myself and generally pick a lower gear than the transmission controller would, enjoying the sporty exhaust note of the straight-six. The air-conditioning is also left on, even though it’s not really required, something I suspect happens quite a lot.
I finally complete the loop and it’s time to see how much fuel I’ve used. It works out to 16.56 litres for 120km. Driving like a lead foot means I have used 6.72 litres more than I did when I was taking it easy. With petrol at $1.14 on the day of the test, the difference works out at $7.66.
If the petrol price stayed constant, which would be a miracle of great proportion, a month of driving (covering1500km) sensibly would cost $139.54. Drive hard and covering the same distance would cost nearly $100 extra, or $235.98. Even before the global economic meltdown it would have been hard to justify such wasteful behaviour, but it seems even more foolish now.
Our test shows the Falcon can be quite an economical car when driven properly, but it also uses a lot of fuel when pushed hard. But it is not just the Falcon that hurts drivers with a heavy right foot.
A few years ago I conducted a similar test using a VY Commodore with 80,000km on the clock. That car had the previous 3.8-litre V6, instead of the very slightly more efficient 3.6-litre V6 which propels the VE Commodore.
The route was slightly flatter, but the idea was the same. By using a feather foot on the first run, the Holden used just 8.35L/100km – a decent figure for a large family car. Adopting a heavy right boot, I managed to turn the Holden into a heavy drinker. Fuel consumption for the second loop worked out to a wallet-crunching 13.0L/100km.
Controlled testing
The NRMA Motoring Research team recently ran a fuel consumption study which came up with some interesting results that expand on our own quick test. They took two four-cylinder Toyota Camry Altise sedans with automatic transmissions and tested them on a dyno to make sure they used the same amount of fuel.
Then they headed to the Eastern Creek race track and set up witches’ hats every 700 metres to simulate traffic lights. The cars then travelled around the track stopping and starting at each hat. One driver eased away carefully from the ‘lights’ then rolled off the throttle and eased up towards the next ‘intersection’. The other driver floored the accelerator and jumped on the brakes late.
When the aggressive driver had used up most of his fuel, the cars headed back to the pits and the calculators were fired up. It turns out the aggressive driver used 34.8 per cent more fuel than the guy who was taking it easy. So all three tests demonstrate that driving like a fool will hurt when it’s time to head for the bowser.
Any fleet manager will also tell you that this kind of driving is terribly hard on tyres, brakes and the drivetrain.
The NRMA team also carried out some interesting tests regarding cruising speed and ballast, coming up with some eyebrow-raising results. You might snigger at the driver doing 90km/h in the slow lane of the highway, but it turns out he or she is likely to be using 16.1 per cent less fuel than someone ripping along at 110km/h. That is the figure the NRMA team came up with using the Camrys over a 400km trip.
The last test included measuring the impact that carrying 500kg of ballast would have on the car, apart from the obvious reduction in performance, compared with an unladen car.
It turns out that carrying the extra weight meant the loaded car used 23.9 per cent more fuel than the standard vehicle.
It goes without saying that any cargo that really isn’t needed should be left at home for the best possible fuel consumption.
NRMA Research has also found that switching the air-conditioning off and winding the windows down can reduce fuel consumption by 10 per cent. Making sure your vehicle is running properly is also key to reducing consumption, especially if your wheels are getting on a bit. The NRMA says that even something as simple as a clogged air filter can increase your car’s consumption by up to five per cent. Also check your tyre pressures to ensure they are pumped up to the pressure specified by the manufacturer which can make a difference of one or two per cent.
NRMA also recommends turning off your engine when stuck in traffic for long periods of time. Some new vehicles available in Europe have built-in stop/start technology which does this for you. This feature alone can reduce fuel consumption by as much as 15 per cent. Removing bullbars, roof racks and any other item that increases drag is another easy way to cut fuel consumption, with estimated savings of up to five per cent.
All these measures help to limit your fuel bill, but being gentle with the accelerator, avoiding sudden braking and flowing with the traffic is the most effective way to limit the pain at the bowser, not to mention the safest and smartest way of getting from A to B.
