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June 14, 2017

Infrequently Asked Questions: Why did cars switch to a curved design?

Long gone are the days of the boxy Cadillac

Take a gander at the cars surrounding you on the Schuylkill next time you're stuck in rush-hour traffic: You'll notice they nearly all feature svelte curves.

But they didn't used to be that way. So, what happened? 

In an effort to understand why those boxier car designs got left in the dust, we reached out to Richard Cohen, professor of mechanical engineering at Temple University, for an explanation. 

Why the transition from boxy cars to the ones we see today that are more curved? Is it an engineering thing?

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Yes. As well as fashion, of course. We've gotten better and better at making fitter and fitter body panels that are also structural -- in uni-body cars. And in order for them to be structural, they have to be packed in ways that will take forces the same way that an aircraft would, in the way they're made -- with [parts that are conducive to that]. Sharper curves are more brittle, but we've found ways to get around that. But also, sharper curves tend to make it easier for them to collapse. So you have all these trade-offs.

When did this transition start?

Oh, that began in the 1980s, when Chrysler came out with K-cars. We've had improving metalware for decades. And you may -- if you follow the industry, they'd been predicting for years and years that we'd be going to aluminum cars to save weight. But aluminum is more expensive and they figured out ways to cut down the weight by making things fitter, as opposed to cutting down weight by going toward more expensive materials.

Any chance a boxier design would come back in fashion?

The Scion could be one example of that, but Ford has a model and so do a few others. There are others with models pretty boxy. I suspect it's not going to come back into fashion for engineering reasons. But for fashion, aesthetic reasons, maybe.

How about the SUV, when they took off in the '00s? That seems like an odd exception.

There are a bunch of things that drive that. One is the mistaken theory that bigger means safer, which isn't necessarily true. Back 40 years ago, you could do an easy correlation that bigger cars were safer because you had a bigger, heavier envelope to protect yourself. But now, with airbags and crush zones and other improved engineering designs, it's not true anymore. And also improvements to rollover protection based on car design and controls on automatics. You can design out most of the rollover situations...

I remember seeing a headline on a safety article not very long ago -- within the past two or three months -- that small cars are just as safe as large cars. Of course, there are people who like driving in a higher cockpit and feel they can see the road better -- but I don't know if that's necessarily [true]. I don't see that as all that relevant today.

Where do you see car design going next?

One thing you can look for in the next few years is the replacement of rearview mirrors on the doors by cameras, saving weight and reducing [coefficient drag] and also reducing frontal area...

There are a number of ways you can save weight and improve gas efficiency. If the Environmental Protection Agency continues to stress that, with the regulations that have been in place for a better fuel economy, then the innovations like cameras [that replace side mirrors] and safety equipment that saves weight will continue to be implemented. If they roll back some of these requirements, as the current Trump Administration seems interested in doing, then I think they'll still be implemented but not as fast. Because these things do cost money and do increase the price of the car, and they're trying to save money as much as possible.

I'm on my second Prius, and the cost of a new Prius has not been going up very fast even though they've been putting more things into each one. And so, if they can slow down the innovation they save money and make more money at the same time.