WHEN Ford launched the new edition of its Mustang car earlier this year, it promised to offer a wide range of variants on the basic model. It did not take long to deliver, recently announcing the revival of a once-popular high-performance version called the King Cobra. But buyers will not be able to order one at their local showroom, according to Jamie Allison at Ford. They will effectively have to customise it themselves. “You open up the Ford performance catalogue and take one of everything,” he said with a grin.

Ford's King Cobra was one of several hundred customised vehicles on display in Las Vegas last week at the Specialty Equipment Marketers Association's (SEMA) annual convention. The SEMA show is currently the second-biggest annual event in Las Vegas, drawing an estimated 140,000 visitors each year. Adaptations that boost car-engine performance are the big draw. Car nuts wandered past more than 1,000 stalls displaying the latest modified exhaust systems, turbochargers and full “crate engines” (which are ready-to-go, high-performance motors that can be dropped into a car such as a Chevrolet Camaro or Honda Civic). But a wide range of other car accessories were also on display, from air fresheners to in-car electronics—which included a high-powered sound system that made the Las Vegas Convention Centre’s rafters shake.

The SEMA show is normally dominated by small manufacturers, some operating out of domestic garages. But big carmakers such as Ford, General Motors, Toyota and Volkswagen have steadily been moving into this market in recent years; BMW and Mercedes-Benz made the leap this year. Manufacturers have come to recognise that tapping into this high-margin area of the car business—especially for performance accessories—can boost their brand's image, as well as profits. Chrysler, for example, has set up eight of its own customisation centres around North America that allow buyers to make extensive modifications to any of their vehicles.

The customisation business in America was probably worth around $33 billion last year and is expected to grow by 4% this year. That is well below a peak of $38 billion recorded in 2007, just before the financial crisis. But sales of accessories for pickups and other light trucks are expected to grow by more than 10% a year. And the market for sports-car accessories is also starting to show signs of recovery. Such growth, combined with near-record attendance at this year’s SEMA show, explains why the big carmakers see moving into this area as a way to restore their sagging profit margins.