Doctor Diesel

Fiddling the figures

Web01In the October issue, David Price asks for advice on choosing a new company car. He states that a lot of his acquaintances cast doubt on the claimed mpg figures quoted by the manufacturer, which is something I have also heard. David also states that the 99g/km carbon dioxide figure equals 75mpg, but that nobody ever achieves that. If it is caused by harder driving being used in the real world, as opposed to the official test figures driving style, does that mean that these cars don’t actually achieve the 99g/km figure either? If the answer is yes, then why should they pay no road tax, when in fact they are putting out more than 100g/km of carbon dioxide in use, as opposed to the laboratory test conditions that are used to record these unachievable figures? I am sure the testing regime has changed in recent years. My Rover 75 CDTi manual had a combined figure of 48.8mpg and this has always appeared to be reasonably easy to achieve, with most owners seeing over 50mpg on a run, providing the car is in good nick. I don’t recall any outcry, say around ten years ago, about unachievable mpg figures but, since the race to sub-100g/km vehicles, there has been a lot of complaints. Obviously, this applies to petrol as well as diesel.
Colin Gray, Telford

Many thanks for your letter Colin. Unfortunately, as I’ve said before, the EC figures are the results of a near meaningless test cycle that was generated many years ago, and which bears very little relevance to real life motoring. The authorities insist that “real life motoring” is not the purpose intended, the test results merely being a method by which one may compare the fuel economy of one car model with another. Unfortunately that argument doesn’t bear too much scrutiny, as some cars seem to be able to offer a closer approach to EC test figures than others! This highlights the fact that some manufacturers are able to programme their engines more cunningly, and get better test figures than others, whilst in real life motoring they might deliver pretty much the same economy. So there is effectively a variation in the level of deceit. Now one can’t totally blame the manufacturers for taking advantage of the system like this, because it’s (mostly) legal and merely, like tax avoidance, taking advantage of loopholes in regulations.

Back in the days of your Rover 75 CDTi (what a splendid car – I had one of the early lower powered CDTs, and loved it dearly – probably one of the best riding cars ever, bar maybe some Mercedes’ when they knew how to make them ride well) they hadn’t learned all the tricks to optimise EC test economy and, as you say, it was possible to get close to EC test figures. What’s annoying is that some of the farcical aspects of the EC test cycles would be so easy to correct, but it’s a sadly typical aspect of EC red tape that such things take years and years to correct. But then the EC as a collective unit needs to convince itself that it’s making progress on reducing emissions, and the EC test figures are the yardstick by which this is judged. So they need the unreal test cycle figures to convince themselves that they are making progress, when in fact the actual progress in reducing emissions, whilst commendable, is unfortunately far less impressive! What nobody seems to be able to get to grips with is the inevitable climb in performance levels and power outputs. It’s always been fairly easy to wipe out yourself, and some other innocent motorist or motorcyclist, or pedestrian, with quite a modest amount of power – say around 80 to 120bhp – but now we’ve got fairly ordinary cars with, for example, 271bhp, 0-62mph in 6.6 seconds, and top speeds of 150mph, which is totally mindless to me, but then I’m getting old and stupid, aren’t I?

I hope this answers some of your questions Colin, and offers some additional thoughts that may or may not be in accord with your own. But I guess if a buyer can afford a top spec V6 Jaguar XF Diesel such as I’ve (oops!) just mentioned, you’re surely not bothered about a few mpg difference between reality and test figures, are you?
Doc Diesel 

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