MSE News: Government miles-per-gallon car figures 'unreliable'

edited 30 November -1 at 1:00AM in Motoring
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  • edited 27 April 2012 at 12:23PM
    cepheuscepheus
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    edited 27 April 2012 at 12:23PM
    "The vehicles were then driven by two experienced engineers over a variety of roads"
    Unfortunately you need a wider range of drivers to get representative figures. Other major influential factors include the amount of start drop driving (sometimes proxied by average speed), and journey length which partly determines the proportion of distance/time the car spends warming up.

    The driving cycles used to measure fuel consumption are designed to simulate these to an extent, but there are so many factors.

    How is the fuel consumption test conducted?
    • The test is outlined in Directive 93/116/EC as amended by Regulation (EC) 692/2008, and provides results that are more than representative of actual average on-road fuel consumption than previous tests. There are two parts: an urban and an extra-urban cycle. The cars tested have to be run-in and must have been driven for at least 1,800 miles (3,000 kilometres) before testing.
    • Urban Cycle
      The urban test cycle is carried out in a laboratory at an ambient temperature of 20oC to 30oC on a rolling road from a cold start, i.e. the engine has not run for several hours. The cycle consists of a series of accelerations, steady speeds, decelerating and idling. Maximum speed is 31mph (50km/h), average speed 12mph (19km/h) and the distance covered is 2.5 miles (4km).
    • Extra-Urban Cycle
      This cycle is conducted immediately following the urban cycle and consists of roughly half steady-speed driving and the remainder accelerations, decelerations, and some idling. Maximum speed is 75mph (120km/h), average speed is 39mph (63 km/h) and the distance covered is 4.3miles (7km).
    • Combined Fuel Consumption Figure
      The combined figure presented is for the urban and extra-urban cycle together. It is therefore an average of the two parts of the test, weighted by the distances covered in each part
  • camajcamaj Forumite
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    Seems like this is PR for What car? than anything else. Any test can be disputed, the point is that all cars must go through identical tests, that is the scientific way of doing it. This allows buyers to assertain what cars are more fuel efficient.

    I see that What Car? neglect to mention that some people are able to get better economy than the official figures. The world record in economic driving is something like 30-40MPG higher than the official MPG for that car, which I believe is a VW Passaat
  • alleycat`alleycat` Forumite
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    My major confusion is why my old VW could do better mpg than my "new" eco version (that has much higher quoted mpg).
    In fact i could beat the manufacturer figures in the old car (passat).

    No such luck in the newer model (I can barely get within -10%).

    The above is based on tank to tank driving on pretty much the same roads over the last decade.

    The stuff coming out of the pipe is cleaner (euro III to euro V) but does the offset in reduced mpg make it an exercise in number fiddling?
  • withabixwithabix Forumite
    9.5K Posts
    As per cepheus's post above, the test is to blame, not the manufacturers or the government.

    The test figures are a means of comparing different vehicles under fixed conditions and nothing more.

    If you want to blame anyone, blame the European Commission - they made the rules.

    To be honest, I don't know why MSE have re-published this non-story.
    British Ex-pat in British Columbia!
  • verityboo wrote: »
    Not really news, just another report confirming what people knew - the manufacturer tests carried out under ideal conditions give better mpg than people achieve in the real world

    So why do I regularly exceed them?
  • Dave_C_2Dave_C_2 Forumite
    1.8K Posts
    Not a comment on the story, but the headline Government miles-per-gallon car figures 'unreliable' is particularly cringe-worthy. Ignoring the unnecessary hyphens, there are such well-known phrases as "fuel economy" and "fuel consumption" which would be much better.

    Dave
  • ReaperReaper Forumite
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    Not sure why the news article about didn't provide a link to the site it is talking about. Here you go:
    http://www.whatcar.com/truempg
  • MeanParentMeanParent Forumite
    128 Posts
    This is a real problem for company car drivers who are refunded mileage by their employers with rates set by HMRC which are based on these inaccurate figures.

    This means that many are seriously out of pocket and there is nothing that can be done. (I have contacted HMRC about this as my car costs 25 pence per mile in fuel but can only claim back 19 pence per mile).
  • colinocolino Forumite
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    MeanParent first thing is that running around in your own car costs you a darn sight more than the petrol costs, don't do it unless you are properly recompensed! Additionally if they only pay you 19ppm, check out Mileage Allowance Relief.
  • MeanParentMeanParent Forumite
    128 Posts
    colino wrote: »
    , check out Mileage Allowance Relief.

    Have done so, it doesn't apply if you have a company car.

    Other half has their own car so I know the cost comparisons. Don't forget company car drivers pay BIK as well which in my case is almost £200 per month.
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