FRANKFURT – If limousine owners are prowling this year's Frankfurt auto show for inspiration to expand their fleets, they should stop by BMW AG's Mini pavilion in Hall 4.

At least in the U.S., it appears every production vehicle – from the Lincoln Town Car and Navigator to the Hummer – is fair game for the limousine conversion business.

So why not a Mini?

The Mini Concept Frankfurt on display here is evidence that BMW designers may have been asking that very question. That is what good designers do: They contemplate the unusual, the far-out and the impossible.

Mini is doing well, selling 700,000 units since its re-launch under Bavarian tutelage three years ago.

The challenge is to keep the product fresh and vibrant, which is difficult to do when the brand itself is tied so directly to a particular body style.

Mini Concept Frankfurt is big.

The brand already has the Mini One, Cooper, Cooper S and convertible versions, as well as the John Cooper Works package, which offers factory installation of aftermarket ornamentation.

With this many variants of essentially the same vehicle, it appears BMW designers had little choice but to contemplate new, upsized dimensions for the concept, while retaining the brand's identity.

BMW officially isn't sharing the concept's spec sheet. But Mini Chief Designer Gert Hildebrand says the wheelbase is 3.1 ins. (8.0 cm) longer than the current production Mini and the concept overall is 7.9 ins. (20.0 cm) longer.

The long wheelbase also gives backseat passengers considerably more legroom than current models and affords an ample rear-cargo hold.

The blunt, chunky front end was designed to meet pedestrian impact regulations taking effect in Europe, and the square-ish backend looks an awful lot like it came from a Detroit SUV design studio.

Instead of the traditional liftgate on current Minis, the Concept Frankfurt has split rear doors that swing open, such as those on the ultra-big Ford Excursion.

Designers consulted their automotive history books and borrowed the split rear door idea from the Mini Traveller, which launched 45 years ago in September 1960.

“Some of you may find this vehicle reminiscent of a classic concept from days gone by,” Michael Ganal, BMW board member, tells the crowd at the concept unveiling.

“It is true – this idea does hark back to history,” Ganal says. “On the other hand, its implementation is guided entirely by the principles of the new Mini brand.”

Mini considers the Frankfurt show the proper venue for this concept because the auto exhibition played a key role in the recent re-launch of the brand. In 1997, it was at the Frankfurt show that BMW displayed a Mini concept for a small group of journalists.

In 2005, the company is striving for 200,000 sales for the year. Through the first eight months, Mini has sold 139,000 units – 16,000 vehicles more than like-2004.