Ever wondered why the official fuel consumption figures are optimistic?

[badass]

http://www.dft.gov.uk/vca/fcb/the-fu...ing-scheme.asp
There's your answer right there.
Ignoring for a second that the urban cycle is highly unrealistic, and would still have been optimistic for urban travel 30 years ago, the tests are run at 20-30 degrees C!
In my car I've seen it do over 40MPG at 70MPH with the air con keeping the cabin around 18 degrees C in the height of summer with curise control on.
It will generally do 34MPG on the same run when it's raining in winter and 35MPG without the rain.
Other cars are similar.

[Knoxville]

It depends as much on how you drive as the conditions on the road in my experience, sometimes the quoted figures are wildly optimistic regardless but from time to time they aren't far off. For instance a friend of mine recently went to pick up his new diesel Honda Civic on lease, with a little bit of motorway and dual carriageway driving then a run through the city centre to get it home his fuel consumption came in at just over 70mpg and the quoted figure is something like 78mpg.

A figure that makes me weep frankly, given that I'm lucky to average anything over 20mpg but c'est la vie! ;-)

[technodean]

Too many factors with fuel consumption, i.e gear change timing (rev's), whether you live in a city (traffic & lights) or the villages. I had an impreza which did better on fuel being ragged around the country side than it did on a school run.

[kalniel]

http://www.dft.gov.uk/vca/fcb/the-fu...ing-scheme.asp
There's your answer right there.
Ignoring for a second that the urban cycle is highly unrealistic, and would still have been optimistic for urban travel 30 years ago, the tests are run at 20-30 degrees C!
In my car I've seen it do over 40MPG at 70MPH with the air con keeping the cabin around 18 degrees C in the height of summer with curise control on.
It will generally do 34MPG on the same run when it's raining in winter and 35MPG without the rain.
Other cars are similar.

Oh it's far worse than that. You're also allowed to use one off-oils, tape up seams, over-inflate tyres, remove various appendages and then knock 4% off your consumption figure for 'tolerance'.

However since I own a car from before when the manufactures learned these tricks, I'm dead on the claimed figures.

[abaxas]

The largest factor is people being unable to operate their cars correctly.

"Others gears are available"
"Accelerator pedal is an analog device, not an on off switch"
etc

[peterb]

Even if the actual figures are not representative of real life, provided the test conditions are similar for two vehicles, the comparative measurement is still of some value.

[KeyboardDemon]

The largest factor is people being unable to operate their cars correctly.

"Others gears are available"
"Accelerator pedal is an analog device, not an on off switch"
etc

I know far too many people that will drive at the same speed until the very last moment when they have to stop at the lights rather than gradually lose speed through the flywheel resistance so that when the lights change they can, assuming there aren't stationary cars in front of them gently accelerate through the green light after maybe selecting a lower gear if it's needed.