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Official MPG Figures Unrealistic, Says UK Auto Magazine

Posted by timothy on from the your-mileage-may-vary dept.

Taco Cowboy (5327) writes "Research carried out by UK consumer magazine What Car? which concluded that official manufacturers' MPG figures are unrealistic. Based on the research, new car buyers in the UK who trust official, government-sanctioned fuel economy figures will pay an average of £1,000 (€1,216) more than they expect on fuel over a three-year period. Since launching True MPG two years ago, What Car? has tested almost 400 cars in real-world conditions, using cutting-edge test equipment and achieving economy figures that are on average 19% lower than the government figures."

11 of 238 comments (clear)

  1. Real-world conditions by Anonymous Coward · · Score: 5, Insightful

    Under-inflated tires, lousy fuel, ignored maintenance, rapid acceleration, more than one occupant / actual cargo, stop-and-go traffic, air pollution, air pressure variation, air temperature variation, elevation variation...

    And these are just a few of the things that would cause your "official" MPG figures to deviate from observations.

    1. Re:Real-world conditions by Chrisq · · Score: 5, Informative

      Under-inflated tires, lousy fuel, ignored maintenance, rapid acceleration, more than one occupant / actual cargo, stop-and-go traffic, air pollution, air pressure variation, air temperature variation, elevation variation...

      And these are just a few of the things that would cause your "official" MPG figures to deviate from observations.

      That's all true, but manufacturers go to great lengths to inflate the figure. They disconnect the alternator, tape up cracks in the bodywork to improve airflow, remove wing mirrors(!), disconnect the brakes to reduce friction and use special oils in the engine to improve efficiency. Figures are not just a bit off but way off. My car has an official figure of 68.9mpg. On a good trip, driving on a flat road at about 70 mph I can get 54, but my usual average is 35 mpg. This is with gentle driving, I can easily take it down to 25 if I don't take care.

    2. Re:Real-world conditions by MightyYar · · Score: 4, Informative

      This story is about European standards which are a bit wacky, but I know they get spot-checked in the US. Hyundai paid out a huge settlement for (apparently honestly) screwing up the testing.

      Remember that your competitors are probably testing your cars, too :)

      --
      W..w..W - Willy Waterloo washes Warren Wiggins who is washing Waldo Woo.
    3. Re:Real-world conditions by Lumpy · · Score: 4, Interesting

      Also set up wrong by the manufacturer. The 2007 honda civic has a highway MPG rating of 40mpg. I regularly get 44-46 while speeding after I fixed their design flaw in the rear end. they set the car with significant negative rear camber and with about 2 degrees of toe, I reset it to zero and zero and not only did fuel mileage numbers skyrocket by 10-15% but rear tire wear dropped to zero or undetectable. From what I can tell they STILL sell civics with this flaw, and the Honda Fit as well suffers from it.

      Granted I only have about 10,000 miles of testing on this new adjustment, but there is no measurable tire wear on the rear and my wife has been driving it to work and back daily on a 45 mile commute as if she was in an indy car race trying to do 75-80mph. Gas mileage is measured two ways. 1st odometer+fuel used at the pump and a Scan Gauge I installed. they are within 1mpg of each other.

      There is only one drawback to the change, the car is slightly more sensitive to steering input. I notice it, she does not. I am going to next add 2 degree of camber from the front to make it closer to zero as well as remove 2 degree of toe that may make the steering a bit too twitchy but you never know until you try. right now it has more than 8 degrees of camber and what looks like 9 degrees of toe. so the removal of that should further boost highway fuel economy but not as significantly as the rear end change. The rear was doing nothing but scrubbing the tires all the time, as most civic owners will tell you they have to replace the rear tires a lot as they start to cup, this is because of the dramatic flaw in how the rear end is set up on all 8th gen Civics.

      Oh and I do these alignment changes in my garage, the "laser alignment" crap is nothing more than a scam. You can do a better alignment on your garage floor or driveway than the "experts" with the "highly advanced laser system" can.

      --
      Do not look at laser with remaining good eye.
    4. Re:Real-world conditions by KozmoStevnNaut · · Score: 5, Informative

      Also set up wrong by the manufacturer. The 2007 honda civic has a highway MPG rating of 40mpg. I regularly get 44-46 while speeding after I fixed their design flaw in the rear end. they set the car with significant negative rear camber and with about 2 degrees of toe, I reset it to zero and zero and not only did fuel mileage numbers skyrocket by 10-15% but rear tire wear dropped to zero or undetectable. From what I can tell they STILL sell civics with this flaw, and the Honda Fit as well suffers from it.

      That's not a flaw, it's a deliberate design to improve stability and handling, especially during mid-corner corrections and emergency maneuvers. The slight toe-in also helps straight line stability.

      My car (Peugeot 406) is setup like that as well, it has enough negative rear camber that it is immediately noticeable when looking at the car. If you try to "correct" this by dialing out the camber, the car will be less stable over mid-corner bumps, and the small amount of passive rear steering built in the rear suspension will be negated, further worsening the handling.

      What you have done is make your car go from being relatively neutral in corners, to having positive camber when the suspension is loaded up. If you've ever read "Unsafe at any speed" or seen an old VW Beetle corner hard, you will know that having positive camber is one of the most dangerous situations you can be in. So you've actually made your car significantly less safe, all for the sake of a few MPG. Congratulations, I hope you're proud.

      --
      Eat the rich.
  2. Re:What's that in KPL? by jspayne · · Score: 4, Informative

    Your concern might be less of a troll if you knew that the standard metric measure for fuel economy isn't km/l, but rather l / 100km.

  3. No fuel economy figures are going be right by Anonymous Coward · · Score: 5, Insightful

    Isn't the more important thing that the all the cars figures are comparable.

  4. watch the program on 5th gear by lkcl · · Score: 4, Interesting

    before making *any* judgement you *need* to watch the program on 5th gear which covers exactly this question in some detail. basically the test was designed originally for people driving sensibly, and it was designed i think well over 20 possibly even 30 years ago. so it has a very *very* gentle acceleration and deceleration curve. gentle acceleration because that is not only fuel-efficient but also the cars of that time simply could not accelerate that much, and gentle braking because again that is more fuel-efficient but also because if you had drum brakes they would overheat.

    people no longer drive sensibly: they are more aggressive with other drivers (not keeping a safe distance), they put their foot down hard on the accelerator and they put their foot down hard on the brake. also as the cars are more reliable they tend to not maintain them properly: until i watched another program on 5th gear about how badly old oil affects fuel economy and the lifetime of the engine i had absolutely no intention of changing oil regularly in the decade-year-old cars i buy.

    so, in effect, people should stop complaining and start driving in more fuel-efficient ways... *regardless* of how aggressive the person behind them gets when they set off from the lights at the same acceleration rate as a 40 tonne cargo lorry. that's the other person's problem.

    1. Re:watch the program on 5th gear by rolfwind · · Score: 5, Funny

      and it was designed i think well over 20 possibly even 30 years ago. so it has a very *very* gentle acceleration and deceleration curve. gentle acceleration because that is not only fuel-efficient but also the cars of that time simply could not accelerate that much...

      WTF are you blabbering on about? Cars from 1980 or 1990 could not accelerate that much?

      You must be a young kid or something, but not everything before your time was primitive by virtue of you not having come along yet.

  5. Re:Which is why sometimes small engines ... by CeasedCaring · · Score: 4, Informative

    In the UK, road tax has not been linked to displacement since March 2001 - it's all about emissions (CO2 in g/km) these days. See https://www.gov.uk/vehicle-tax...

  6. Driving faster help my MPG ... YMMV by perpenso · · Score: 4, Interesting

    Probably also driving too fast... European emission standards require testing at 90km/h, while the max speed in most EU countries is 120 or 130km/h

    I'm in the U.S. and my car is rated 22mph city 29 mph highway. The city rating is dead on. The highway rating is off, I actually get 34 mph rather than the stated 29. My typical highway is designated 65 mph and when traffic is light it is practical to do 75 mph. At 75 mph I get 34. The rating of 29 may be based on obsolete 1970's 55 mph standards.

    Maybe 55 was optimal with 1970's auto technology but it doesn't seem so today, at least for me. And of course YMMV is quite appropriate here.