Official MPG Figures Unrealistic, Says UK Auto Magazine 238
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."
Real-world conditions (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.
Re:Real-world conditions (Score:3, Insightful)
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
No fuel economy figures are going be right (Score:5, Insightful)
Isn't the more important thing that the all the cars figures are comparable.
We knew the gist already (Score:4, Insightful)
We pretty much already knew that the MPG we saw on the sticker was higher than the MPG we would actually be getting. Hence the phrase "your mileage may vary."
But we also know that the sticker MPG numbers are good for comparing among similar cars, and that's mostly how we use the sticker MPGs. Kudos and thanks to 'What Car?' for calculating the 19% offset figure. I wonder if they could tell us how the offset varies among different types of cars. Maybe SUVs vs econoboxes vs sports cars have somewhat different offsets.
BTW, I would bet that different driving styles, lead foot vs hypermiling [ecomodder.com], makes a bigger differnece than the 19% calculated by 'What Car?'
This is not new news (Score:3, Insightful)
Re:We knew the gist already (Score:2, Insightful)
> But we also know that the sticker MPG numbers are good for comparing among similar cars,
No, you don't know that. You assume that.
When the benchmark doesn't test the things you care about then you can not count on a linear correspondence between the benchmark performance and performance on what you want to measure.
Think of it this way - the manufacturers are "teaching to the test" when they design their cars now. A student who only memorizes the test questions isn't going to have a real knowledge of anything that isn't on the test.
Re:Which is why sometimes small engines ... (Score:4, Insightful)
A lot of the "new generation" of cars will have small turbocharged engines with direct injection and variable valve timing. Most will develop over 200Nm torque from below 2000rpm, not peaky at all. In fact, a lot of these cars with these engines are already on the road and have proven themselves both reliable and fuel efficient, as long as the owners actually drive them properly.
My car is decidedly old-tech in comparison, with a 2.2L naturally-aspirated 4-cylinder, rated at 8.8L/100km (27.7mpg). I average 9.0L/100km (26.1mpg) in mostly city and motorway driving, with ~160,000km on the odometer. I drive normally, stick to the speed limit or 5-10 over depending on the situation, and try to look ahead and anticipate traffic. It really isn't that hard to get very close to the ideal fuel consumption figures, you just have to relearn how to drive instead of going full-throttle/full-brake all the time.
Re:What's that in KPL? (Score:4, Insightful)
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.
While km/L is less common, it certainly does appear as an alternative measure in many countries, particularly to allow people to compare it to mpg metrics (as the GP was suggesting here, since the title of this story is about "MPG"). You are correct that in many countries, L/100km is standard.
Before we get the standard debate about this crap that comes up every time this topic comes around, let me just point out that the reciprocal relationship between these two measurements doesn't mean one is "more correct" than the other. Rather, both will give intuitive results for different questions or given different constraints.
For example, if you're buying a car primarily for commuting, gas consumption per distance (e.g., L/100km) will give you an intuitive sense of your fuel cost, since your daily distance is relatively fixed. If your L/100km doubles, your fuel cost for fixed commutes will double.
On the other hand, if you're buying a car primarily for occasional longer trips and not using it for regular commuting, distance per gas unit (e.g., mpg or km/L) will give you a more intuitive sense of how far you'll be able to travel with the same gas budget. People buying a car only for occasional trips probably are more likely to care about how far they can go with a given amount of fuel rather than how the fuel cost will vary for a fixed distance. If your MPG doubles, you can go twice as far with the same amount of fuel.
Different metrics are useful for different things. These two have a very clear relationship, but when non-math-literate people are comparing the raw numbers, one can be better than another in making decisions depending on the situation.