Smaller cars not necessarily the most efficient

The small car, small cost notion may be a myth. Research by Emissions Analytics discovered bigger cars were actually closer to their claimed fuel economy figures.

The data company drove 500 vehicles, 250 petrol and 250 diesel, for three hours on British roads to give a more realistic representation of real-world use. It found that on average manufacturer fuel economy figures were 18 per cent lower than advertised.

Smaller engines showed the biggest discrepancy, with vehicles in the 0- to 1.-litre category achieving 36 per cent few miles per gallon. That worked out at 38.6 instead of 60.3mpg. 21 per cent fewer miles were achieved In the 1- to 2-litre category, averaging 46.7mpg instead of 59.1.

Larger engines in the 2- 3-litre category came out as the worst fuel guzzlers, unsurprisingly, but the claimed figures were only 15 per cent out on the claimed ─ 45 instead of 52.9mpg.

Emissions Analytics said the difference is down to how manufacturer estimates are worked out. Tests in a laboratory with low rates of acceleration and slower speeds will never give an accurate representation of everyday driving.

“For maximum fuel economy you should look for a one to three-litre engine, as these will return around 45-46mpg. To avoid being too disappointed with the result, pick a two to three-litre vehicle as it will be only 15 per cent worse than you were told you could achieve,” Emissions Analytics said in a newsletter.

RAC Foundation director Stephen Glaister said the finding show consumers are being misled: “These astonishing figures only fuel the debate on the worth of official mpg data. Well over two million new cars will be sold in the UK this year, with small vehicles topping the sales chart. But how many drivers will actually get what they think they have paid for? The answer, in terms of fuel efficiency, must be not many.”

WhatCar has tested some of the most frugal cars on the road and found very few that claim to more than 60mpg actually do. Number one, the consumer magazine claims, is the Kia Rio 1.1 CRDi Ecodynamics, which scored 70.6mpg compared with its claimed 88.3mpg.