Indeed. "manufacturers can tweak their cars' ECU maps and gearing to perform well in the tests." Its on a rolling road, only 16kms in extent, and SFAIK, carried out by the maker. As there are no standards for hybrids, certain manufacturers produce fairy-tale numbers. Possibly due to tweaking the battery power to gain as much as possible from running off-engine. Hence the laughable figures for RR and Lexus, 2 tonne plus, barn-like frontal area vehicles, with apparently lower CO2 emissions than a Jazz or other small, light, modest engined cars.

Thus highlighting the ludicrous method adopted! And resulting in a lower VED/evasion of congestion charges for guzzlers.

I don't know how recent your X types were, but my mate's 2008 X type 2.2 D estate does 38mpg, maybe getting just over 40 on a decent run. He's quite disappointed. My BMW 318D touring (also 2008, 143 BHP) averages 49 mpg in the summer and 46-47 in the winter. I can just get over 50 on a decent run dring reasonable gently. According to BMW I should get over 60. On a mega gentle country drive, imagining an egg between my foot and the gas pedal, only acheived mid 50s. I wouldn't want to drive like that normally, it was not really fe, except on an empty road.

These manufacturers' figures are complete fiction. as mentioned there is no air resistance at all, and the acceleration required to do the test is very gentle. I ignore all manufacturers' figures and look for a road test that has an actual number. I don't really care too much how they driove, at least I know that doing some reasonable driving it is possible to get what the road test man got. Can we have more road tests with real mpgs please.

I reckon the old system, where we had fixed 56mph and so on figures were more representative. There was no acceleration involved, but you were pretty sure that if you drove at 56 mph, or 70 or whatever, you would get close to the manufacturer's quoted consumption. For mostly motorway driving it was a very good guide. They scrapped that on the grounds it was not representative of normal driving. Now look what we've got.

Edited by Sparrow on 26/03/2011 at 11:49

So how should mpg be tested?

Manufacturers will tweak their cars to achieve the best results whatever test you use.

The figures are for purely for comparison, but I have never had huge discrepancies between urban and combined figures with any vehicle I've owned.

putting your foot down shoots a tonne of unburnt diesel out of the exhaust, which really brings the figures down around town.

I'm not sure. Black smoke looks bad but there's very little fuel value in it. I'm not sure that acceleration in itself hurts economy if you use the gears properly. High speed and braking are what kill mileage. I still hear people claiming to get 50+mpg in a full size car at 90mph-and it just isn't true!

Actually this thread is hilarious-some of the misconceptions regarding the NEDC beggar belief: "The rolling road doesn't include air resistence"!

"Isn't it outrageous that the manufaccturers have tweaked the car so that I can enjoy a VED cut and BIK tax cuts??".

Morons.

Edited by unthrottled on 12/07/2011 at 16:24

The OP said:

"

Apart from WHICH magazine, very few reviewers of new cars take manufacturers to task for the ridiculous claims they make for CO2 and mpg. It is very hard to take any of these figures seriously as car makers appear to have carte blanche to make all sorts of false claims without anyone seriously this fantasy world, far removed from what you should expect."

A ridiculous claim. Manufacturers just report what their cars achieved in tests. Anyone who believes these tests are real word and is annoyed should spend 15 minutes reading how they are done and stop complaining on a forum...

I dont know about co2 but my MPG figure exceeds the official average of 37mpg.

I have no trouble averaging 42-43mpg average on my journeys.

Yet in previous cars, same driving style, same mannor, same route my MPG was about 38-39mpg when the official average was 45mpg.

So perhaps it depends on the car.

Edited by OldSkoOL on 13/07/2011 at 11:43

This argument has been had before. Its very difficult to ever give a definitive figure for fuel economy and emissions, yes the test methods may be stupid but its probably more accurate than anything else. The variable real world conditions that you'll encounter in your car ownership are pretty impossible to put into a standardised test. So they test all cars indoors on the same methods and take the average from that, now in the real world there will be different factors. Aerodynamics of the vehicle, the speed you drive at, the types of tyres on the car, the inflation rate of those tyres, your gear change ratio's, your day-to-day use of the car (if its used primarily for short trips it'll be less efficient, fact). Whether the road is wet or dry. Wind resistance. Temperature. How much weight is in the vehicle. Whether the Air Con is on or not, whether the windows are up or down. The drivers ability to read the road. The sorts of roads you drive on etc etc etc all of these have an impact on fuel economy and there will never be a test thorough enough to give a definitive figure. Unless every car was tested on a pre-determined route of the same length involving every type of road, testing it with a full load, testing it with just the driver, testing it with and without cargo, with and without air con, in summer and then in winter, on a windy day and then on a calm day, testing it in the rain, testing it in the dry etc oh and all of them would have to be done by the same driver driving the same way (the squishy bit behind the wheel does still have a bearing on how the vehicle performs) you'll never be able to make it fully accurate.

Like if you get a car, drive it quickly with harsh acceleration and harsh braking and use it constantly for short trips on a wet day with a boot full of junk and your Air con on then you will not achieve the manufacturers quoted average. Even if you drive with an empty load on a fine day with just you in the car you still might not, even if you drive very carefully you still might not, as the aerodynamics, tyres, road conditions etc could still all play a part. The EU doesnt know where/when/how you're going to use the vehicle when you buy it, they put these figures there as a guess, a rough idea, to give the customer some idea of what to expect which is better than nothing at all. When calculating whether a car will be viable to run on your mileage, head over to fuel-economy.co.uk and use their calculators, but when entering mpg, be conservative. If it says it does 47.1 then put 42 in, dont rely entirely on a machine's average reading.

They can make pretty definitive tests for how you'll fare in an accident, they can pretty much guarantee the reliability of cars (in the 60s people didnt expect cars to actually work all the time, now we demand it, and usually get it) so if the worst thing you can fault them on is their fuel economy figures arent exact, then thats pretty good going.

As for VED i personally preferred the old system of under 1.5 is one rate and over 1.5 is another, people will say "yes but a 1.6 and a 6litre were then treated the same" yes well holes still appear the way it is now. I do agree there are some good sides to the new system, the low-tax cars are a very nice proposition but as with ANY system it cannot ever fully cover everything.

According to its official figures, my car's emissions is 259g per km, pushing it very narrowly into VED Band M at £460 for a 12 month disc. An 09 plate Ford Focus 1.6 TDCi Zetec comes into VED Band C, with 115g per km, weighing in at just £30 a year. Sounds great.

But if i cover 5000 miles in my car that means total emissions of 2083.9 Kilograms.

If the Focus covers 15,000 miles that means total emissions of 2776.1 kilograms.

Obviously that makes the Focus the kinder car to the planet (if you believe in all that stuff) seeing as it covered far more miles, polluting much less per mile and that is why it is rewarded with lower VED with it being more frugal and effecient, cant argue with that and thats obviously what the system is set up for but the fact is The Focus will have done more environmental damage in a year than my S-Type but will have cost around 6% of the S-Type's VED rate to tax for the year.

In many cases the economical diesels which will be used for heavy mileage can pollute more than the bigger cars which are typically bought by people with lower mileage yet the highest polluter per year will be charged less tax. But of course as ive always said we all have access to this information before we buy a car, i know a Focus Diesel doing three times my mileage will pollute more yet im the most severely punished by the tax man but i had the choice, like we do in a free nation, of whether to purchase that vehicle or not. If i objected that heavily i had the option to not buy it.

Edited by jamie745 on 14/07/2011 at 01:54

Nothings changed my mind, my point was the same as it is now, that you have a choice of whether to buy that car or not. Ultimatley the purchaser of the Focus in that scenario wins in the long run, they travelled further and were taxed less. That car is obviously the most efficient and thats what the system is set up to reward. The main hole in the plan is the fact that these economical cars are generally purchased (diesels especially) by people who will be doing heavy mileage, and cars like mine are typically bought by people who wont, so typically, on average, the Focus TDCi's, 407 HDi's etc up and down the land will be polluting more throughout their lifetimes as they will be used more.

Im not against the system, i'd be happy if they just left it alone, when a Government keeps fiddling its difficult to plan for their next move, if they just leave it alone then we know what to expect. I like the way the system can be "beaten" in some way, like with the maths i demonstrated above, i like it, i think thats all part of it. And it encourages people to buy cars like the Focus TDCi which is obviously the point of the system. With any system there should always be a method of playing it, beating it and getting something for nothing, its part of it.

I was expecting a long dissection of my fuel economy segment regarding official figures from you, im surprised to see it did not materialise, about how im all wrong or something, as usually you come up with something :P

No we wont. We just...we just wont. I dont think i said anything too technical, most of it is common sense and information gained and applied in many conversations ive had with people who go "i dont get the mpg it says in the book!! scandal scandal!!"