As you might have guessed, BMW has been toying around with the lightweight construction material for some time, seeing just how far it could push the envelop and what practical applications it could have. In this case, it turns out that, back around 2003, the Bavarian automaker re-constructed a first-gen X5 sport-ute with a carbon fiber reinforced plastic (CFRP) unibody. Every panel on the X5 was replaced with CFRP, save the doors which retained their conventional steel construction. The result was a weight savings of 440 pounds, without – according to BMW – sacrificing structural rigidity and crash-worthiness.
Of course the carbon X5 was never put into production, but it reportedly underwent some 40,000 kilometers (25,000 miles) of testing, and the knowledge gleaned will surely find its way into BMW's production vehicles in the future.
[Source: BMW Blog]