Thursday, 19 May 2011

It's the (fuel) economy, stupid!

Have you ever bought a new car, admired the impressive fuel economy figures plastered over the front window, got the car home, driven it around for a few months and realised that it is almost impossible to reach those fuel economy figures doing anything like normal driving? Yeah, me too.

I have always assumed that the fuel economy figures were based on some kind of track - one that simulates both city and driving conditions - and that the good people from the government testing laboratories put on their grandpa hats and driving gloves and diligently drive the cars around the track for a few hundred kilometres whilst monitoring how much fuel they are using.


Turns out that rather than a track, it is an indoor rolling-road dynamometer (a glorified treadmill for cars) that the cars are "driven" on. And how far are these cars driven? A grand total of 11 km over 20 minutes. That's right, to calculate urban, extra-urban and combined fuel economy figures, most cars will use less than 1 litre of fuel.


OK that's not, technically, exactly right*. They test at least three cars. So for most cars, the testers will burn through at least 2 L of fuel getting the fuel economy figures. Impressed?

I assume that the test is precise enough to give accurate, relative fuel consumption values over a range of vehicles but it's just, you know, a little disappointing. I was also worried that because the test is run without the car actually moving, there is no wind resistance and the aerodynamics of the car are therefore not taken into account. So I read the Vehicle Standard (Australian Design Rule 81/02 - Fuel Consumption Labelling for Light Vehicles) 2008** and, actually, not only do they account for wind resistance, but also rolling resistance. These are combined into a term called the running resistance, and the dynamometer is set up to provide this resistance, which varies depending on the speed. Actually, I take back my criticism; that is pretty cool.

I guess it's not so much that the testing conditions are fabricated to make it impossible to reach those economy figures, it's just that the roads are full of lead-footed, over-loading, non-tyre-pressure-checking, air-conditioner-overusing, unnecessary-roof-rack-installing wankers, with you, me and anyone bigger than me being the only exceptions.

Thanks to the latest issue of Choice Magazine for the heads up.

*Which therefore means it is, technically, dead wrong.
**Appendix B: Annex 7: Section 6 if you are interested. You probably aren't.


MeatPopsicle said...

They need to add a fine print that says *Figures should be use comparisons only.

Daryl said...

To be fair, it does say "Actual fuel consumption and CO2 emissions depend on factors such as traffic conditions, vehicle condition and how you drive."