Jeep is preparing to make the most radical changes to its iconic Wrangler off-roader in the model's history to drag it into line with 21st century expectations for fuel economy, crash protection and refinement.

The next model is due in 2015 and Jeep's engineering program manager for Wrangler, David Vrabel, concedes the Detroit-based car maker needs to make major changes to the model that is still an identifiable descendant of the Willys Jeep used by the US Army during World War II.

This historical link has enabled Jeep for decades to resist significantly changing the Wrangler in engineering and design terms, and it's a heritage that its owners value highly, Vrabel says.

"Wrangler does great business for us, and the people that drive it love it for exactly what it is," Vrabel says. "There's no need to change simply to boost sales."

Recently I took a two-day trip that encompassed testing off-road trails and steep mountain passes in the brand's rugged heartland in the US state of Colorado, driving both the Wrangler and Grand Cherokee models. Notably, around two in every three cars encountered coming the other way was a Wrangler, confirming the model's strong popularity in the US with serious off-road enthusiasts.

But with the next Wrangler currently deep in the design process, Vrabel concedes that change is inevitable. "The CAFE (corporate average fuel economy) regulations are making life more difficult for us," he says.

Jeep recently fitted a petrol-powered 3.6-litre V6 to the current model Wrangler that is significantly more powerful (209kW and 347Nm) and slightly more efficient than the unit it replaced in automatic form. But its combined fuel use average of 11.3 litres per 100km is still off the pace compared with other off-roaders it competes against.

This is most keenly felt in the US, where the Wrangler is offered solely with the petrol V6.

Asked if Jeep would consider substituting the petrol V6 that effortlessly bullocked the Wrangler up steep, shifting mountain passes during our Colorado drive program with a more efficient turbocharged four-cylinder unit, Vrabel replied: "Maybe. It's something we are definitely thinking about, but we also need to consider what that means in driveability terms."

Jeep and its sister company Chrysler are owned by Italian maker Fiat, presenting easy access to engines such as the 1.7-litre turbo four that powers the Alfa Romeo Giulietta QV with 173kW and 340Nm. It uses 7.6L/100km in the Alfa but that would rise when allied with the bigger Wrangler.

The Wrangler's instantly recognisable design ethic - including the bluff, upright grille and jutting, squared-off front bumper - has barely changed in decades but Vrabel says toughening pedestrian impact laws could force a radical rethink. "Does that mean we have to put more of a slant on the grille to make it more pedestrian friendly?" Vrabel says. "Maybe we do, we're looking at how to make that work better."

The Wrangler's other obvious Achilles heel, on-road driving refinement, will also come under scrutiny, but any improvements will not come at the expense of its astonishing off-road competence, Vrabel says.

And while many current owners cherish the Wrangler's no-nonsense, utilitarian interior complete with hard-wearing seat cloths and scrubbable hard plastics, greater cabin refinement and functionality is also on there whiteboard for discussion.

One thing unlikely to change, though, is the second gear lever that shifts the drivetrain into low-range gearing for heavy-duty off-road work, with Vrabel ruling out changing to a push-button system such as the one used in the Grand Cherokee or a rotary dial used in some workhorse utes.

"We get very strongly from our owners that they like slotting their Wrangler into low-range the old-fashioned way and we don't see a reason to change," he says. 

-Fairfax News Aust