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MIT: To Get Better Gas Mileage, Cars Need Less Power, Weight

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2011 Fuel Economy Labels

2011 Fuel Economy Labels

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In recent years, the quest for high gas mileage has become an important factor for new car buyers, automakers, and legislators alike. 

But has gas mileage really improved over the past 30 years, and what do automakers really need to do in order to ensure their cars meet tough new Corporate Average Fuel Economy targets by 2025? 

According to MIT economist Christopher Knittel, the answer is simple: maintain the same rate of automotive technological innovation we’ve seen since 1980s while simultaneously replicating the average weight and power of new cars sold 30 years ago. 

Has Gas Mileage Changed?

Thirty years ago, the U.S. was recovering from the second major oil crisis to hit the nation. 

With gas prices still high, high gas mileage cars like the 1982 Volkswagen Rabbit proved a popular choice for those wanting to save as much at the pump as possible, while older cars like the original 1973 Honda Civic offered used car buyers a way to avoid high fuel bills. 

Both of these examples, along with many other older cars, are capable of producing gas mileage rivaling or even beating modern-day fuel sippers like the 2012 Chevrolet Sonic. 

In fact, if you look at the change in gas mileage between a car made in 2006 and 1980, there’s an average fuel economy increase of just 15 percent, while average curb weights have increased by 26 percent, and power by a massive 107 percent. 

Larger, Faster, Safer 

Why the disparity between power and weight increases and fuel economy? 

It’s simple. Cars have got a whole lot more complex. Thirty years ago, satellite navigation systems and complex entertainment systems were unheard of. And electric windows, crumple zones and airbags were considered high ticket items on luxury cars like the 1981 Mercedes-Benz S-Class. 

As more safety and entertainment features are added to a car, so the weight increases. In order to compensate, automakers have had to increase engine power.

Honda Earth Dreams Technology engine

Honda Earth Dreams Technology engine

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What we’ve been left with, Knittel explains, are larger, faster, safer cars whose engines are actually 60 percent more efficient than engines produced 30 years ago. But because modern day cars are so much heavier and require more energy to move, any gas mileage improvements in engine design are not as great as they could be. 

The Solutions

Although Knittel praises developments in fuel injection technology, engine control systems, lighter engine components and variable-speed transmissions his report, he also concludes that making cars smaller and less powerful is the key to better fuel economy. 

According to his own calculations, Knittel says automakers have already built engines that are technically capable of meeting 2025 CAFE standards, but need to reduce both the curb weight and power output of the average vehicle by 25 percent in order to transfer that gas mileage from the laboratory and onto the road.  

In other words, Knittel wants cars to go on a diet, or go back to the same weight and power output they had in the 1980s.

source: Popular Mechanics

source: Popular Mechanics

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In addition, Knittel advocates higher gas taxes, and a change in consumer preferences driven by governmental policy changes.

Incorrectly applied though, bad policy could make matters worse.  “If you force people to buy more fuel-efficient cars through CAFE standards, you actually get what’s called ‘rebount’, and they rive more than they would have,” he cautioned. 

The Reality

Thanks to developments in carbon-composite technologies, automakers have already started to make cars lighter. But a 25 percent drop in curb weight is a big challenge, especially if current safety and entertainment levels are to be kept. 

And power? Academically, Knittel’s research makes sense, but we’re not sure the average car buyer is ready to give up the extra horsepower we’ve all become so used to. 

We think a better solution lies in the world of plug-in vehicles, combining small gasoline engines with efficient electric motors to increase gas mileage and reduce emissions, but what do you think? 

Let us know in the Comments below.

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Comments (7)
  1. DUH!

  2. Amazing, what a revelation, who would have ever thought of that. I'll bet it was paid for by a government grant.

  3. One approach is to increase fuel prices through higher taxes that reflect the damage to the environment. A carbon tax (emissions rating/distance driven or vehicle weight) on personal automobiles that would be refunded on taxis, public transport and commercial vehicles.
    Another is to increase traffic enforcement using traffic cameras to reduce highway speeds.

    These all are used in Europe.

    A more likely approach is for government to regulate. As in past crises, a tax on air-conditioning (introduced at $100 in Canada in 1977 but never increased to reflect inflation) is one example. They could tax power windows, power seats, heated seats, etc.

  4. I have no desire for 85 hp. 2 litre engines so why not tax based on the size of the motor i.e. $10,000/litre for engines ove 3 litres? I even remember the late David E Davis while at Automobile Magazine I believe noting how adequate the 3 litre engine was citing cars like the Taurus SHO, Maxima, etc. To avoid retooling to some degree make it 3.8 l if you like.

  5. I agree with smaller and lighter and have been saying the same for a long time ,, keep the cars lighter and lower, mandate cars to 3.8 litre and trucks to 5.7l and also put weight limits on non commercial trucks of 4500 lbs curb weight for 1/2 tons and 5500 for 1 tons and all diesels must have idle time limits of 3 minutes or less. weight and frontal arae are the biggest drag and fuel cost items , we dont need all these crossovers with a 6.5 foot tall roof and 1 foot of ground clearence . dont allow trucks of over 5500 lbs and 130 inch wheelbase into downtown core areas without a commercial business liscence This would prevent all the large 4 door monstrosities from cluttering up streets and burning fuel at a rate of 3-6 miles per gal

  6. In July I purchased a Ford Focus with the F package and the 2.0 engine. I have driven the car 21,000 miles. It averages 35.1 m/g overall. the aerodynamics and 6 speed auto transmission makes it slip thru the air and transmits horsepower to the road very efficiently. I also have a '07 F150 truck and it gets 18 m/g. It does not slip thru the air efficiently. It seems to me that lighter vehicles with thrifty six or eight speed transmissions are the key design element for high mileage. Also, I buy Ford products because they are imported from Michigan and we need to buy American made products. Ford did not participate in the bail out. c

  7. so less weight increases there is a revelation. Haven't' we known that since the beginning of increasing performance of, well, nearly everything? Someone took a basic physics class!!!!

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