[AlanHo]

I am interested to see the economy given for the i30 diesel here - it so happens I assumed 55 mpg when I ordered my new car. It appears that is what I am likely to get.

I have little doubt that the manufacturers are all tuning cars to get the best out of the government tests - rather than tune for best results for normal driving




http://www.dailymail.co.uk/news/article-2135884/Why-drivers-rely-miles-gallon-figures.html

[Doggie 1]

It's an area that probably needs to be looked at by governing bodies because it makes the figures almost meaningless, other than as a comparison with the meaningless figures from other car manufacturers.
It would be good to be able to look at the obligitory sticker on the windscreen and know that you were probably going to get close to that quoted figure in the real world.

[Shambles]

^-- as Dave says, only useful when used in comparison, if all the figures are "overstated", all the time, by the same amount.

If What Car? could test and publish results for all current vehicles, then that'd be the chart to base your purchase on.

I have to admit to not caring a hoot about my economy, though as it happens I do drive in a frugal manner.

Alan, of course I'm not surprised at your synicism with regard to this topic... it's well documented. 

However, if I'm able to achieve equal or better than advertised then surely it's all up to the driver?  I can, so I'm not as sure as you that it's a conspiracy.

The tests predictably and understandably try to present best figures (and probably do) so that cars can be compared apples to apples. I think they are.

Something that cannot be considered in a test that has no wind resistance included is the drag coefficient of the car.  Most cars are in the vicinity of .3xx so this can probably be ignored.

Going back to my initial point though, if I can better the official figure why is it so maligned by you and others? Presumably because you are not prepared to drive as do I. Surely your choice but does this mean the figures are wrong just because they are attainable only by those prepared to go all out?

I'd like you to understand that none of this is personal as I do see you as a fellow "analyst" and so I offer my alternative view for you to consisder.

[Phil №❶]

Pip uses 40 psi too Alan. I wonder how much difference that makes 

[Doggie 1]

However, if I'm able to achieve equal or better than advertised then surely it's all up to the driver?  I can, so I'm not as sure as you that it's a conspiracy.

It's partly up to the driver but primarily influenced by environment and not all environments are the same.
The laboratory tests are conducted under abnormal conditions and whilst some can, the majority of drivers can't replicate them in real world driving conditions.

.. and whilst some can, the majority of drivers can't replicate them in real world driving conditions.

So surely by this statement you agree that the figures are attainable? If you were selling cars would you say something like "these are the figures we measured but good luck getting them "

I'm as synical as the next guy but sometimes one needs to be realistic.

I'm really prepared to bite on the thread title: There really is no Myth!!

[Doggie 1]

.. and whilst some can, the majority of drivers can't replicate them in real world driving conditions.

So surely by this statement you agree that the figures are attainable? If you were selling cars would you say something like "these are the figures we measured but good luck getting them "

I'm as synical as the next guy but sometimes one needs to be realistic.

I'm really prepared to bite on the thread title: There really is no Myth!!

Yes, but not in the majority of cases, as I said. 
I don't think the figures are indicative but it is fun trying to achieve (and better) them.

[Dazzler]

I found about a .3 LPH difference in favour of the mainland compared to Tasmania with the Hybrid which I put down to the generally flater terrain and slightly lower highway speed limits (Less % of 110 speed limits in the Eastern States than in Tassie)

My 6.1 Average over 5000 kms was only .1 above the official overall figure of 6.0 for the 2010 Hybrid.. If I got .3 less in our CRDi had we done the same trip in that it would have bought us down to 5.1 Lph compared with an official overall of 4.7 Lph (I know that is drawing a long bow)

The Hybrid's Stop Start technology probably "liked" the  stop start driving condtions in Melbourne, Sydney and Brisbane too..

[tla]

I think I've previously posted this link to a Popular Mechanics article "Mileage Moment of Truth: We Put 40 MPG Claims to the Test":

http://www.popularmechanics.com/cars/news/fuel-economy/mileage-moment-of-truth-we-put-40-mpg-claims-to-the-test-6651300

I remember reading that the US EPA recently tweaked their laboratory test results to get MPG values that better match real-world results.

Additionally, wind resistance is factored into the results.  I guess it's done by including the car's Cd into the calculations.

[Dazzler]

Thanks tla .. that seems logical 

[beerman]

I would have thought the one place you would get close is on the highway, after all, there isn't much that can stuff up there. Bang in the speed and cruse.

I find I get about 6-6.2 in the Auto CW. Which is close to the combined figure of 5.8.

Although I would say about 75% of my driving is on the highway (though I tend to sit on 120).

[Phil №❶]

Unfortunately, in order to level out the playing field, the consumption figures have become very obscure. At a motor show, it is useful to compare figures between makes but experience shows that  most people will not achieve these figures at all.

In Australia, I would prefer that all makes and models be driven around an agreed test track. Mt Panorama would be terrific, but it is a public road, so a bit hard to arrange. The test could be in 2 parts, 1 @ 60kmh, the other @ 100 kmh both 100 km distance. The driving technique should NOT be spirited driving, simply logging up 100km as smoothly as possible. Having measured the 2 fuel consumptions, you have your figure. The only stipulation would be a dry track. Although there is no stop start factored into the 60kmh test, this is such a random event for each driver it is best eliminated. That way, a true comparison between makes and models cam be obtained.
Worldwide, there would only be the need for test tracks in say Europe, America, Asia, or countries could use our data if they wished. The Mt Panorama track is not flat, I think there is a 400m climb up the mountain and this would typically reflect the normal driving that some people would encounter. If your country is flat, then your fuel consumption will possibly be less that that stated, that would be a bonus for you.

I volunteer to perform the tests of all new cars. 

Naturally, the test results would differ in each region, but the purchasers of vehicles in each country would have a real figure, rather than a laboratory figure. I would also expect the at least 25% of owners would be able to actually achieve these figures, rather than the rare few (pip), who can achieve the current formulation.

Thoughts anyone 

[2i30s]

the fuel consumption figures could well be calculated with the engine on a stand in an engine dyno room. 
altitude and air temperature can also make a massive difference in fuel consumption and horsepower. 

[Phil №❶]

the fuel consumption figures could well be calculated with the engine on a stand in an engine dyno room. 
altitude and air temperature can also make a massive difference in fuel consumption and horsepower. 

That's how they do it now isn't it.
Personally, I'd ignore altitude & temperature, but for those who have an issue, there must be engineering constants that can be applied to compensate. 

[AlanHo]

I would agree that a practical test over a set route with a maximum set overall time would be the most useful.

Even better if a car could be obtained from a main dealer who was not pre-advised in order to make sure that it had not been tinkered with for maximum economy or the tyres blown up to 50 psi or any additives put in in the fuel.

The vehicle should also carry an independent observer and run without the air con in action to ensure a level playing field across nations.  Freewheeling or tailgating in the slipstream of other vehicles should not be allowed.

[Doggie 1]

And heavy woollen socks should be banned too - it could adversely affect the outcome.

[rustynutz]

It all sounds too hard......I'm happy enough with what they use now.....

[Dazzler]

It all sounds too hard......I'm happy enough with what they use now.....

  I think it is a fairly level playing field 

[FatBoy]

IMHO the figures that are used in Australia enable Australian motorists to compare apples to apples.  Therefore I would expect to use more fuel in a car that has a combined of 12.1 l/100km to one that has 8.3 l/100km.  Would I expect to get those figures?  No, they are for comparison purposes only.  The actual test is listed here:

http://news.drive.com.au/drive/buying-tips/qa-official-fuel-consumption-figures-20101216-18yws.html

Leave it the way it is, particularly how it is in Australia.

[2i30s]

but how many of us bought an i30 for its fuel economy alone. 

[FatBoy]

but how many of us bought an i30 for its fuel economy alone. 

Not I, but I did COMPARE the stated fuel usage of the cars I was looking at. 

[2i30s]

but how many of us bought an i30 for its fuel economy alone. 

Not I, but I did COMPARE the stated fuel usage of the cars I was looking at.

same slim. 

[succulant]

but how many of us bought an i30 for its fuel economy alone. 

Its not the only reason but its a big contributing factor for me doing 15-20k miles a year.

[baroudeur]

I would agree that a practical test over a set route with a maximum set overall time would be the most useful.

Which is exactly how the commercial vehicle magazines carry out their testing.

BTW I get 58 mpg on  long distance motorway running but drop to 42-45 mpg in  all-urban driving.
I did record 62 mpg  - brim to brim - over 232 miles from Dusseldorf to Dunkirk running at legal maximum speed - (unlimited in Germany where I achieved 100 mph) on  most of the all-motorway journey.  Too short to be truly accurate but acceptable.

BTW2.  The salesman told me I would get 65+ mpg regularly.   I told him I would be happy if I got 55 mpg regularly which now seems to be the overall average consumption!