It's all-new, and it's still fast -- but it's not lighter or more fuel-efficient. Did Ford make a mistake with the 2015 Mustang? Source: Ford.

Is Ford (NYSE:F) taking a bigger risk than we thought with the all-new 2015 Mustang?

When the new Mustang was first unveiled last December, it appeared the automaker had played it safe. Sure, the styling had evolved, but not too far. The interior was nicer, but still familiar. 

From powertrains to colors to options packages, the message seemed pretty clear: The new Mustang is improved in a lot of ways, but it isn't really different.

But now that we've learned more about the new pony, we're starting to hear complaints from a few quarters: It's bigger. It's heavier. It's less fuel-efficient.

Has Ford made a mistake here? 

Other Fords are losing weight, but the Mustang didn't
It's true that the 2015 Mustang has gained a little bit of weight over its predecessor. Ford says the weight gain comes mostly from additions such as the all-new independent rear suspension and larger brakes, among other things.

We're not talking hundreds of pounds here: A 2015 Mustang coupe with the EcoBoost four-cylinder engine weighs just six pounds more than a 2014 Mustang coupe with the base V6.  Other models gained more, but the increases are still fairly modest. The biggest gain, 87 pounds, comes in GT models equipped with manual transmission. 

The all-new 2015 Mustang went into production in Flat Rock, Michigan, this week. Source: Ford.

But "heavier" is never an advantage with a performance-oriented car such as the Mustang. All things being equal, a lighter car will accelerate faster and handle better. 

And Ford is emphasizing weight reduction in other models -- in a big way. Consider Ford's other major debut this year, the all-new F-150 pickup. The 2015 F-150 is considerably lighter than the truck it replaces, thanks to the use of aluminum body panels. It's expected to get significantly better mileage than the outgoing truck.

So why didn't Ford take more dramatic steps to reduce the Mustang's weight? Probably because executives didn't want the Mustang to change much.

Why Ford was reluctant to make big changes to the Mustang
Here's the biggest change for the new Mustang: Unlike the current version, and all past Mustangs, this 2015 model is a global product. 

Ford plans to sell its new pony in Europe, China, Australia, and many other parts of the world, not as a high-priced exotic import, but as a regular part of the company's lineup.

That's new. And the company's decision to make the car a global model led to some discussion: What kind of Mustang should we roll out to the world? 

The new Mustang's interior looks good, and includes thoughtful touches and premium materials, while sticking to the classic Mustang formula. Source: Ford.

I've heard that Ford originally planned to make the new Mustang much smaller in order to make it more appealing abroad. By European standards at least, the Mustang is a pretty big car. A smaller Mustang would surely have been lighter, with better fuel-economy numbers.

But last December, when the new Mustang was unveiled, then-CEO Alan Mulally told me that Ford's research had shown that foreign buyers didn't want a different, smaller Mustang.  They wanted the Mustang, just as Americans have come to know it, in all of its rowdy, V8-powered glory. They didn't want the product to change. (And needless to say, neither did the Mustang's many American fans.)

So Ford shifted gears and created a new Mustang that improves on the old model by being faster, more refined, and more comfortable, but doesn't really change the formula.

I suspect that will turn out to be the right approach. But it means the new Mustang isn't lighter, it's not smaller, and it doesn't get better fuel economy.

Do you think that was the right move? Scroll down to leave a comment with your thoughts.

John Rosevear owns shares of Ford. The Motley Fool recommends and owns shares of Ford. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.