The minute after you sign the papers on a new car or truck, do you spend a few more grand customizing it?

It may sound odd to aging Baby Boomers, but it's a growing trend.

According to recent Ford research, 50% of buyers aged 16 to 24 plan to personalize their vehicles the moment they buy them. This “millennial” generation also is expected to buy 2 million new vehicles in 2006 and 4 million in 2010.

They personalize everything from sneakers to cell phones, and as they grow old enough to buy cars, they're personalizing them, too.

According to Ford, today's youngest generation of auto buyers is the most diverse in history. In fact, 50% are non-Caucasian, with many opinion leaders hailing from major urban areas.

This group's heroes, tastes and activities are different from much of white suburbia, leaving many typical automotive engineers and designers scratching their heads over why anyone would want to put chromed 28-in. wheels with tires the thickness of a rubber band on an off-road vehicle.

But the tuner business isn't about practicality and common sense. It's about style, going fast and not looking like anyone or anything else.

Aftermarket add-ons related to engine performance, appearance accessories and handling equipment are a huge and growing business, hitting $27 billion in 2002 according to the Specialty Equipment Market Assn. So OEMs are putting the SEMA crowd in their sights as profit margins on standard production models dwindle.

Detroit's Big Three once sneered at the giant annual SEMA exposition in Las Vegas. But as they've watched Asian auto makers build a large following of free-spending tuners, they, too, are embracing the event.

Sometimes it's a little painful to watch, like being in a hot new nightclub and seeing a balding, middle-aged white guy trying to dance and act hip.

But unlike those pathetic guys, this is something the Big Three need to keep doing until they get it right. They're trying hard.

Ford had the largest exhibit ever for an auto maker at SEMA, a giant display highlighted by 14 customized versions of its new Ford F-150. GM North America President Gary Cowger presided over GM's large booth, proudly announcing that GM is the first OEM to offer a full line of “dubs” (tuner slang for oversize wheels).

The reason for all this excess is simple: money.

OEMs need to catch more tuner customers in their own dealership showrooms and sell them the highly profitable customizing parts they want, rather than watching them walk out the door to an independent shop. GM already sells its Hummer H2 with an average of $5,000 worth of dealer add-ons. It needs to expand that success throughout its model line, as does every auto maker.

But if the Big Three, in particular, do it right, they might be able to sell new customers enough custom parts to make up for the $3,000 they put on the hood to make the sale. For young consumers intent on immediately customizing their new rides, that extra money might turn into the most powerful incentive of all.