Hi Doc,
Having just finished the December issue of Diesel Car, I was very interested in the long term car tests. We have just replaced our 407 SW with a 508 (SW? Doc) which will have to last for the next four or five years. So we are looking five years down the road for a second-hand replacement, which is what makes the long term test so interesting. Looking at the manufacturer mpg figures and what might be the “real world” averages obtained by your testers, they seem to be quite varied. Then I came to the letters section and first up was a letter raising the same question. It occurs to me that, by adding a simple percentage figure to the mpg figure from your testers, there would be an immediate indication to your readers of the true economy they are likely to obtain should they purchase any particular vehicle. So, if they purchased a Mitsubishi ASX, they might be likely to obtain 99 per cent of the manufacturer’s official combined figure. However, if they purchased a Grand C4 Picasso they may only see 69 per cent of the official figures. I know that different drivers have different driving styles but, over a long term test, most of your test drivers should drive a similar distance over a variety of British roads and, unless one driver spends a large majority of their mileage either in town or on a motorway, the figures should give a balanced indication of what an average driver could expect during their ownership of any particular vehicle.
Thanks for reading this and I hope the above proves to be of some interest.
Peter Goddard
P.S. I started reading Diesel Car about 25 years ago and still pick up the occasional copy when I see an article which particularly interests me. I am pleased to see that the articles are still as well written and full of interest as they were “back in the day”.

Nice of you to drop in on Diesel Car from time to time Peter… why don’t you get a “season ticket” subscription at a very keen price? That’s my marketing bit done now! There really isn’t a huge difference between the shortfalls in real life mpg with most cars. It’s a pretty crude way of doing it, but if you assumed that you might attain the official urban figure in general motoring, you wouldn’t be too far wrong. But I fear there is nevertheless a much bigger difference between individual drivers in terms of lifestyle, type of motoring, and driving style. Some people will never get good mpg figures, because they don’t really know how to drive, don’t appreciate the way that internal combustion engines work, don’t understand things like torque and gearing, and don’t really concentrate on their driving. That’s a pretty damning comment, I fear, but hopefully it won’t offend very many Diesel Car readers! I really think that a lot of drivers wonder what I’m doing when I lift off the accelerator when I see a red traffic light 200 yards ahead – they just don’t understand or want to understand the principle of conservation of momentum, and the waste of fuel and energy when you convert momentum into waste heat by braking. I could go on… and I often do, as you will know Peter.

If we take a selection of cars – let’s say a Fiesta 1.6 TDCi Econetic, a Volkswagen Golf 2.0 TDI 150, and a Jaguar XF 2.2d 161bhp, I think you could quite easily encounter owners whose fuel economy varied respectively anywhere between 45 and 70mpg, 40 and 65mpg, and 35 and 55mpg; there’s no way that you could accurately say to any individual, without knowing how and where they drive, where within those ranges they might fit. I don’t know all our Diesel Car contributors that well but, knowing that there are wide differences between where they live, the sort of lives they lead, and the way they drive, I think that their long-term fuel economy results are therefore little guide to what you might get from any of the cars that they are driving. But many thanks for your letter, bringing up an interesting point for me to ramble on about! Good luck with the 508 – it’s a somewhat overlooked model with a lot of good points – not the least that you can buy a fairly young used one at a very keen price, which I hope that you did! Best regards,
Doc Diesel