When trying to reinvent the Ford Explorer for the 2011 model year, designers and engineers at Ford Motor found themselves at cross-purposes.

The designers were aiming to capture the essence of the Explorer's rugged, go-anywhere attitude in a modern interpretation of an American sport-utility vehicle. The engineers had a different objective: making an SUV with jaw-dropping fuel economy that would reverse Explorer's current standing as a neighborhood pariah.

The problem they faced was that in order to optimize aerodynamics, and thus, fuel efficiency, the Explorer would need to be egg-shaped, with a squared-off rear end. The designers wanted the upright, athletic stance Explorer was known for.

Their boss, product development chief Derrick Kuzak, stuck the two camps in a room--a stadium-sized, aerodynamic wind tunnel -- to sort it out with a clay model, one millimeter at a time.

Kuzak, the man behind Ford's recent string of successful new vehicles, needed to prove to Chief Executive Alan Mulally that his people could reinvent an Explorer with 25 per cent better fuel economy without losing the characteristics that made it so popular in the past.

In the 1990s the Explorer was an American icon and the source of most of Ford's profits. But by mid-2008, when gas topped US$4 a gallon, SUVs fell out of favor, and small cars and crossovers became the choice of smart consumers. Last year Ford sold just 52,190 Explorers, down from 445,157 in 2000.

Nowadays, the four-wheel-drive Explorer, which gets 13 mpg in the city and 19 mpg on the highway, is a has-been in the Ford showroom. It's outsold nearly 2-1 by the Ford Edge, a more car-like crossover, and more than 3-1 by the smaller and more efficient Ford Escape crossover. A third vehicle, the Ford Flex, rounds out Ford's crossover lineup as a minivan substitute for large families.

But Ford's market research showed there was still a place for Explorer in the market, albeit not at the 400,000-unit sales level. "Explorer is a strong name, right up there with F-series and Mustang," said James Holland, the vehicle's chief engineer. With 3.5 million Explorers still on the road today, Ford found people still craved the sense of adventure provided by SUVs that cushy crossovers can't match. "We saw a window of opportunity, a sweet spot that was not being served," Holland said.

But could they really develop a guilt-free Explorer? In an industry where carmakers agonize over every one-tenth mpg improvement in fuel economy, a 25% leap would be a huge challenge.

The company had already made two key decisions that would make the new Explorer less thirsty. Instead of a heavy pickup truck frame, the new Explorer would be built on a lighter car chassis, the same one used by the Ford Taurus. And Ford outfitted it with a turbocharged, 2-liter, 4-cylinder engine (the smallest engine ever in an Explorer, but with more horsepower than the current 6-cylinder).

There were other changes, too, like reducing tire friction, switching to electric power steering, and making the four-wheel-drive system 50 pounds lighter, all of which chipped away at the Explorer's thirst for gasoline.

But those changes still got them only about halfway to their fuel economy goal, which is why designers and engineers found themselves butting heads in the wind tunnel over the tiniest styling details.

"The aerodynamics guys wanted a squared-off rear end," to improve the flow of air over the vehicle, said chief designer Mel Betancourt. But he and his designers wanted a slanted lift-gate for a more modern look, a view that was affirmed in consumer focus groups. To compensate, they added a spoiler at the top of the rear lift-gate. When they turned on the fans in the wind tunnel, however, they discovered turbulence in the air just under the spoiler, creating unwanted drag.

That's when they began brainstorming. Holland and Betancourt figured out they wouldn't have to change the design if they created a tiny dimple along the edge of the spoiler to prevent air from recirculating behind the vehicle. Less drag, better fuel economy.

As a trade-off, Betancourt's design team agreed to install a cleverly hidden aerodynamic shield in the wheel wells to direct wind around the rear tires.

They also raked the windshield back dramatically--from 34.4 degrees on the current Explorer, to 29.7 degrees on the new model -- to improve aerodynamics. The result is instead of a boxy SUV, the new Explorer is more athletic-looking.

Overall, Ford improved the aerodynamics by 12 per cent, adding 1.4 miles per gallon to Explorer's fuel economy--a huge leap by industry standards.

Company officials won't give a specific mpg for the new model, but say those aerodynamic improvements, along with the more-efficient engine and car-like structure, will make the Explorer the most efficient SUV on the road.

Ford will take the wraps off the new design later this summer. It goes on sale this fall.