MPG FIGURES

Isn’t it time this corporate fiction is abandoned?

Carmakers always want the best-possible ofcial mpg fgures. OK, imagine a company whose factory is on top of a mountain. They invite the ofcial European fuel-testing scientist to the plant. The car emerges from the gate, the tank is brimmed, the trip meter zeroed, and he’s given a gentle shove to roll of down the hill. On he sails, dropping and dropping, just every so often fring the engine when the hill’s not steep enough to carry him. Finally, when the road levels out, he draws to a stop, measures the total fuel used, divides by the total distance – including the bits where he was coasting – and that’s the mpg.

Not very fair, huh? Sure enough, it’s not allowed. But something else with the exact same efect is not only allowed but positively encouraged. It’s the test for plug-in hybrids. Instead of using a long hill to give them a free run, they use electrical power from a battery. A normal car’s consumption test is run over 6.9 miles, but a plug-in hybrid’s can be far longer, by an amount determined by the electric range. They begin the test with the battery full, and fnish it with it empty. This electrical energy is blithely ignored. So is any CO2 from the power station that charged it.

Go look up – no, for your sanity, don’t – UNECE regulation 101, which lays down the exact procedure for the ofcial mpg and CO2 tests. It’s 100 pages long. First they measure, on a level track, the aero drag and rolling resistance, then they feed that resistance into an indoors rolling-road dyno and ‘drive’ the car on the rollers through the test cycle. Actually, they don’t measure fuel consumption at all. They measure CO2 from the exhaust and calculate consumption from there, because a litre of petrol or diesel embodies a known amount of carbon to be oxidised.

If you’ve ever wondered why you don’t get anywhere near as good economy as the ofcial fgure, check the speed-againsttime graph for the test. The hardest acceleration phase is 0–70kph (0–44mph) in a not-exactly-blazing 41 seconds. Drive like an actual human, and you’ll drink more fuel – and emit in proportion more CO2 – than the test says you will.

The CO2 number matters because it’s a climate-change gas that we as a society have committed to reducing. Hence the tax incentives on so-called ‘low carbon’ cars. The related fuel- economy number hits home in a far less abstract way, because it predicts the actual cost of keeping the tank full. But it’s all cobblers if that complex testing produces a number that bears no relation to the real world.

You used to hear the argument that at least the test provided a basis for fair comparison, because all cars were fattered to the same degree. But that’s no longer the case. Plug-in cars get fattered to an extraordinary extra degree, as if they were rolling down a mountain, by ignoring the electrical energy. Like when your doctor asks for your alcohol intake, and you count the beer but don’t mention the wine. A BMW i8 might be more economical than a Porsche 911, but is it, as the ofcial test says, four and a half times better? C’mon. And because the test fatters plug-ins, they get huge tax incentives. So makers have invested heavily in R&D, and are selling them as loss leaders, because they are being mandated by governments worldwide to reduce their corporate average fuel consumption.

All to do well in a test that’s a charade. Firstly, because of the CO2 from power stations, which in Europe negates about half the supposed advantage of electricity versus petrol. And second because the test for plug-ins is designed on the assumption that on average after just 25km (16 miles) of driving with the engine on, you’ll stop and recharge the battery. How realistic is that? After all, the very point of plug-in hybrids is to allow you to drive a long way untethered by the mains cable.

“Is the i8 really four and a half times more economical than the 911?”