New Gas Mileage Rules Will Reshape What Americans Drive: Aerodynamics And Weight

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2014 Mercedes-Benz CLA 45 AMG, First Drive, Bilster Berg

2014 Mercedes-Benz CLA 45 AMG, First Drive, Bilster Berg

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No, we won't all be driving golf carts.

In fact, as cars change over the next 12 years to meet much tougher fuel-economy rules, automakers will likely do their best to keep the changes invisible.

Your next vehicles will deliver better gas mileage than ever before, no matter how large or small they are.

By 2025, the industry has agreed to meet an overall corporate average fuel economy (CAFE) level of 54.5 mpg.

That translates to about a 42-mpg combined EPA rating on the window sticker, due to differences in how fuel efficiency is calculated.

That's lower than three different Toyota Prius hybrid models achieve today, but the average includes everything from minicars to full-size pickup trucks.

So what are the technologies that will let automakers comply with the gas-mileage rules--and how will they change your next car?

We've broken this rundown into three parts:

Today, we'll look at the increasingly slippery shapes cars will take on--many of which you probably won't notice--and the diets they'll be put on to lose excess weight.

In both cases, the changes may not seem as radical as you imagine.


One of the easiest ways to save fuel is to make a car smoother and slipperier above 40 mph, when the energy required to overcome wind resistance starts to rise.

Every new vehicle, from sleek supercars to bluff, blocky-looking pickup trucks, now spends hundreds or thousands of hours in the wind tunnel.

Body designers and aerodynamicists refine every element, from wing mirrors to small "spats" at the corners of the wheel arches, to reduce the airflow turbulence that causes drag.

Wind tunnel testing the MINI Cooper John Cooper Works GP

Wind tunnel testing the MINI Cooper John Cooper Works GP

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Airflow is key over 40 mph

By guiding the air smoothly over and around the car, reducing the swirls and eddies where air gets trapped, less energy is required to push the car through the air.

A byproduct is that the car can also become quieter, with less wind noise apparent inside.

One way you can confirm just how aerodynamic a new car is: Take it on the freeway and open one window--say the driver's--and then another one on the other side, perhaps the right rear.

In many cars, the imbalance in airflow on the two sides produces a fast, unpleasant drumming or buffeting sound.

That old tip about opening your windows to save fuel by keeping the ventilation off?

Definitely no longer accurate; efficient aerodynamics save more fuel at speed than the newest electric air-condioning compressors use.

2011 Chevrolet Cruze Eco

2011 Chevrolet Cruze Eco

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Grille shutters, undertrays

Two simple, invisible ways that automakers can smooth out the airflow over new cars are adding active grille shutters and smooth undertrays.

First launched on the 2011 Chevrolet Cruze Eco, active grille shutters sit behind the grille and close off the airflow through the radiator when it's not needed for engine cooling.

That cuts turbulence (that air has to escape from the engine compartment somewhere) by simply routing the airflow around the car's nose and over the rest of the body.

GM now uses those active grille shutters on several different Buick and Chevrolet models, and Chrysler has added them to its latest 2013 Ram1500 pickup truck for the same reason.

As for smooth undertrays, they're simple, durable composite panels that cover the various components hanging underneath the car's floorpan.

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