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Where are those fuel figures coming from?

23.05.2014

IF YOU’RE anything like me and have always wondered where car manufactures get their claimed fuel consumption and performance figures from, you’ll find what I’m about to tell you, quite interesting. You see, most of the time, we simply accept the claimed power/torque outputs of a car as well as the performance/fuel economy figures.

The problem is, these figures are not always accurate. That’s why there are thousands of comparative videos on YouTube and write-ups in newspapers, magazines and on line, comparing vehicles in the real world. I mean, the people who provide us with the claimed figures are the ones who produce and sell us the car. Are we going to believe them? Of course the figures they claim will be as low/high/impressive as they dare. After all, they want to sell us a vehicle, not provide us with an objective review of its real-world performance.

Don’t think for a second that I’m accusing motor manufacturers of providing false information to the consumer. The figures that each company puts forward have been achieved, just not in the same way we may think. Take European cars as an example. The European Union (EU) has a vehicle-testing procedure for fuel consumption called the New European Driving Cycle. The test is conducted under laboratory conditions where different driving environments are simulated. The fuel consumptions achieved in these tests are carried out without the power-draining electronics fitted to the car that we buy and will obviously be lower than those given in the real world.

In the USA the Environmental Protection Agency (EPA) recently discovered that a certain manufacturer was providing fuel consumption figures that weren’t achievable in any instance. It was discovered that an error was made by the testing crew, employed by the manufacturer. As a result, consumers who purchased the vehicles were refunded all the money they’d spent over and above the claimed consumption.

It’s very important to note that many fuel consumption test results published by manufacturers also assume that we spend around 55 percent of our time driving in the urban environment and 45 percent on the highway. I know that I spend the majority of my time in the urban environment and a smaller portion on the highway.

We can’t all rush out now and claim our petrol money back from the manufacturers after reading this - that’s just plain silly! Our vehicles can come very close to achieving the claimed consumption figures that many manufacturers put out there. But being employed citizens who need to get to work within a reasonable time, driving like an Eco fundi simply won’t cut it. So, we drive with a bit more vigour and therefore our consumption is slightly higher.

My personal vehicle as well as our long-term Civic, here at Autodealer, both struggle to achieve the factory claimed consumption figures but at the same time they’re not very far off. We have to remember, living in Gauteng is tough on our cars; our climate is far warmer than Europe’s and our traffic is often more severe. Johannesburg was labelled the fifth most congested city in the world during a 2012 study conducted by IBM. And now, many more commuters are using back roads in order to avoid e-tolls and there’s been slow transport infrastructure growth and who knows, it may even be worse now in 2014.

The air also is thin meaning that both turbocharged - and especially naturally aspirated cars - need to work harder so as to create that air/fuel mixture that makes an internal combustion engine work. This is where the performance side of things comes in, too. Up here at the reef, all vehicles are affected by the altitude. In Johannesburg we’re over 1 600 metres above sea level while Pretoria is around 1 400 meters above.

This means that a non-turbo car produces up to 18 percent less power up here meaning the car has to be driven harder to get acceptable performance for everyday driving. A turbo car, thanks to forced air induction, will lose a small amount of power. However, the engine has to work harder to make that power by compensating for the lack of air available. We should accept that where we live, our cars are slower and heavier on fuel.

Article written by Sean Nurse
23.05.2014
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