Understanding Fuel Efficiency

Less is more - that's the mantra for today's automotive industry. Fuel efficiency, sometimes also referred to as fuel economy, is the measure of how far a vehicle can travel with a litre of fuel.

On this side of the world, the unit of measurement is in litres/100 km or km/litre. You may have come across overseas literature which uses miles per gallon (mpg) instead.

When researching fuel economy, one must be careful to read the fine print, as there are several different standards used in different countries to measure a vehicle's fuel efficiency.

Testing the same vehicle under different standards can yield significantly different results, sometimes up to 40 per cent!

In Europe, the European Union states follow the 'New European Driving Cycle' (NEDC) standard. The 'Urban' cycle test involves a series of acceleration, deceleration and idling. The maximum driving speed is 50km/h, with an average of 19km/h over a distance of 4km. The 'Extra Urban' cycle mimics highway driving at a maximum speed of 120km/h, averaging 63km/h over a distance of 7km.

Results of the 'Urban' cycle and 'Extra Urban' cycle are then averaged for the 'Combined' cycle, which is most reflective of actual driving conditions.

Meanwhile in Japan, manufacturers have to follow the 'JC08 Driving Mode', which involves driving at an average speed of 24.4 km/h (including idling period) over a total distance of 8.171 km, with a maximum speed of 81.6 km/h.

Over in the US, the Environmental Protection Agency (EPA) mandates a slightly more complicated method. EPA figures are derived from up to five different test conditions, taking into account not just speed but different ambient temperatures and increased load on the car’s air-conditioning. City driving figures are then adjusted downwards by 10 per cent and highway driving by 22 per cent to better reflect real-world driving conditions during which the vehicle speed is not constant.

Fuel efficiency tests for the purpose of meeting government regulations are done under very strict conditions. All vehicles must be tested using the same reference fuel, which often has to be imported from a single certified supplier. The vehicle must also be acclimatised overnight and the ambient temperature in the auditor-certified laboratory is strictly controlled.

Back home in Malaysia, the government has yet to gazette any one particular standard for fuel efficiency testing, and this is probably why some manufacturers do not publish information on fuel efficiency for some models sold here.

As manufacturers often adapt their models according to local exhaust emission regulations, fuel quality, road conditions and driving preferences, the same model sold in another country may not necessarily exhibit the same fuel efficiency as its twin sold in Malaysia.

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