Lightweighting: Putting Our Cars on a Diet

This week’s post is from Michael Brylawski who heads MOVE – The Transportation Innovation Group at the Rocky Mountain Institute.

Dieting is no less than an American obsession. As much as we like to eat, we’re constantly inundated with the latest fad for losing weight.
 
But while we’re at least attempting to get a handle on our love handles, America has an even larger weight problem: our cars and trucks. Over the last two decades the weight of our light vehicle fleet has been increasing faster than our waistlines. Take the midsized SUV: the average 2007 model weighs almost 500 lbs more than one from 1990. Even the average compact car has packed on 374 pounds during the same time period. That’s enough extra pounds to make even an offensive lineman blush.
 
Overall, RMI estimates that the average vehicle has seen almost a 20% weight increase over the last 20 years. Two-thirds of this weight gain has come from cars getting denser, not bigger in size. In other words, it’s not just people shifting into larger vehicles that is causing the automotive pounds to accumulate—it is the vehicles themselves getting heavier with bigger engines, more content, thicker steel, and heavier parts.
 
Why should we care? For vehicles and almost every transportation platform, weight is the enemy of efficiency, as Amory Lovins explained in his blog “Profitably Kicking the Oil Habit”.
 
In a world of $3 a gallon gas and tightening carbon regulations, cars need to be put on a diet. But how can they shed pounds without compromising safety, utility, and performance? What is the automotive equivalent of “eating right and exercise”?
 
As for “eating right,” just as the food we put in our bodies affects our mass, so do the materials we put into our cars affect our cars’ mass. Advanced materials such as aluminum and carbon-fiber composites offer superior strength and stiffness per pound to mild steel, the dominant material used in cars today. US automakers have made several concept aluminum and composite vehicles that are almost half the mass of a comparable steel vehicle without compromising size or safety.
 
“Exercise” in automotive world is the discipline engineers need to have while designing cars. Just substituting lightweight materials for heavier ones won’t get you the weight savings you need to dramatically affect efficiency. Designers and engineers have to pay careful attention to how they design every part in the car.

Take seats: you may not realize they make up 10-15% of a car’s mass. Interiors supplier Johnson Controls has used sharp design to reinvent the automotive seat for enhanced comfort and radical lightweighting. It’s Genus concept not only is a fraction of the mass of a conventional seat, it increases occupant room (through a thinner seat back) and improves ergonomics.
 
JCI’s improvement in utility and comfort shows that lightweighting need not mean sacrifice—the benefits of redesigning parts and systems can open new opportunities. And all things being equal, a lightweight car will handle better, brake shorter, and accelerate faster.
 
Lastly, it is important to note that reducing vehicle weight does not mean you have to reduce vehicle size. This is the biggest misconception about lightweighting—that shedding pounds means forcing people into cars too small for their lifestyles and families. With advanced materials like aluminum and innovative design methods, we can have our efficiency and use it too: you can have lightweight large sedans, crossovers, even SUVs. Lightweight does not have to mean small, just as “fit” people can be of various heights.

Now that hybrid-electric vehicles such as the Prius have caught on, we at RMI see significantly lighter vehicles as the next big breakthrough in the automotive industry. Fasten your seatbelts, as Detroit, Stuttgart, and Tokyo are all about to enroll in automotive “weight watchers.”

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Michael Brylawski heads MOVE – The Transportation Innovation Group at the Rocky Mountain Institute. His diverse work portfolio includes positions at a top-tier management-consulting firm, a Fortune 50 aerospace company, and several roles within RMI in the 1990s, including RMI’s spinoff Hypercar, Inc. (now Fiberforge). He is now leading RMI’s efforts to transform the transportation sector with radically more efficient platforms.