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Thread: The truth about claimed mpg figures

  1. #1
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    The truth about claimed mpg figures

    Found thins and thought it would be interesting for those who aren't happy with claimed mpg figures

    http://www.autocar.co.uk/blogs/still...=true#comments

    Firstly, they are not measured on the road, but in a lab on a rolling road, and not by calculating the actual fuel used, but the exhaust emissions and from that working out the economy.

    The car conducts two routes, over a total distance of just 6.8 miles. All of which is on the flat. The urban figure is measured over 2.5 miles, at a maximum speed of 31mph and an average of 12mph. The extra-urban test is 4.3 miles at speeds of up to 75mph, but averaging 39mph. The combined figure is simply a weighted average of the two.

    The tests are run without air-con, lighting or audio equipment and, because the tests have to accommodate commercial vehicles, the acceleration components allow 50 seconds to reach 62mph, which is not how most people drive.

    All of which Iím sure is very scientific and repeatable, but is it representative? We certainly very rarely get close to the claimed figures in our tests, which may not have the total accuracy of a lab test, but I think are more thorough and realistic of what you, as an owner are likely to achieve.
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  2. #2
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    Well, what a con. No wonder I only get 31mpg out of the claimed 39 on my BMW! Rubbish.

  3. #3
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    Quote Originally Posted by ThatSmarts! View Post
    Well, what a con. No wonder I only get 31mpg out of the claimed 39 on my BMW! Rubbish.
    It's not a con (and I suspect you're teasing ).

    The tests are designed to give an indication of mpg based upon a certain set of circumstances and most importantly, they're repeatable and eliminate human variation.
    Of course, no-one said they had much relevance to real life and that's the 'real' mistake. If people see those figures and expect to be able to match them, they're going to be disappointed. Unless, of course, you can drive in circumstances that match the conditions laid out on the rolling road.

    And lets not forget that manufacturers are far from stupid; they'll tweak a car to get favourable figures for mpg; so where the test allows 50s for acceleration, it'll be on a light throttle, so the engine is programmed to on sip the juice, but in real world, people put their boot down, so the engine is programmed for performance and to hell with economy[1]. Similarly for noise regulations; ever wondered why some cars have a mid-range flat spot? Why are 'active exhaust bypass valves' so popular? Because on a drive by test they stay closed, but when you're raggin' it, they're open for the best noise

    Remember kids, 67% of all statistics are made up on the spot.



    -Lee


    [1] Case in point... my Roadie is remapped (by Red Dot Racing). If I drive exceptionally gently, and in particular, drive off-boost, I can get fairly high mpg figures (50-60). But, driving as I normally do (lead boot) I get rather lower mpg (although still over 40!). My point is that the remap provides an exaggerated example of what all manufacturers do.

  4. #4
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    Well that's me told! Perhaps I'll try a feather-light, tedious acceleration approach to driving for the first week of Smart ownership and see what happens.

  5. #5
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    Quote Originally Posted by ThatSmarts! View Post
    Well that's me told! Perhaps I'll try a feather-light, tedious acceleration approach to driving for the first week of Smart ownership and see what happens.
    Do try it. You'll then get really bored and develop a heavy right foot. Fortunately, Smart cars are blessed with excellent mpg as standard so you don't really need to try. A modified Supra that I used to have was rather different...

    -Lee

  6. #6
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    I seem to be getting around 40mpg in my new fortwo passion and I've only done 700miles in it! I drive mainly town and haven't had a chance to go on any longer trips I'm guessing it will get even better when I eventually run it in haha. And I am a fairly peaceful driver using full auto and mhd.
    Our Lovely Smart baby arrived on the 29th December 2010. Little Ethan Steventon

  7. #7
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    When you get your car, don't get too disheartened with the first couple of thousand mpg. We found it got much better after 5k

    Lee, i think you nailed the problem in the head, in that these are not real life figures. When they are shown as such, then people get angry that they have been mislead
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  8. #8
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    Who am I kidding, I'm going to rag the hell out of it then take the poor thing 400 miles to the lake district in may, no easy life for my smart, I need SPEEEEED!

  9. #9
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    Why does everyone think that you buy a smart just for the claimed mpg? I certainly didn't I would only be a bit hacked off if the mpg was crap, but it isn't!
    Our Lovely Smart baby arrived on the 29th December 2010. Little Ethan Steventon

  10. #10
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    Auto holds on to gears veggy, so when in manual i would be in 4th, auto will still be revving in 3rd
    Smartz Admin staff member - Here to help!

    Having a smart is only the beginning, so why not join in with the community?

    In between smarts at the moment. Had to get something sensible

    - Citroen C4 VTR+ 1.6 HDi 110bhp

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