The gnarly legend of Harley Davidson motorcycles is now more than a century old and has reached cult status. They are a badge brand, a symbol of American-made brawn and independence, a brand experience that offers to hardwire your adrenal glands directly to the throttle of a 1500cc engine as you inhale the freedom of the open road.

Harley is the visceral rumble of their exhaust. They’re a little bit outlaw. Harley, quite simply, kicks ass. And through 105 years of cultural and political change, economic expansion, recession and depression, Harley has been a survivor. Now, with the York County assembly plant hanging in the balance, they’re taking a hard look at the future of their brand.

Unlike a General Motors, for instance, this is a company that knows who they are. Harley Davidson makes big bikes, 750cc engines and larger, the equivalent of two-wheel muscle cars built for cruising. If you’re looking for a dirt bike or a crotch rocket, keep moving because Harley isn’t into that. They know their product and they’ve got a pretty good fix on who buys them. They’re focused on the brawny side of the equation. And they average over 45% market share in the category.

So what’s the problem?

In a nutshell, the loyal customers (and they are fiercely loyal) are getting older every year. The average age of a Harley purchaser has gone from 38 to 46 in about the last ten years. Younger buyers, with less money, are buying cheaper Japanese sport bikes, and leaving the big bike cruisers to the older set.

Despite their leather chaps and free flowing beards, the majority of Harley riders don’t get any further outside the law than going 5 miles an hour over the posted speed limit on their way to dinner at Applebee’s. It doesn’t help that these Boomer bikers have just watched their 401K and home equity take a tumble. Harley bikes are a luxury item, even in the best of times.

But if Harley can’t market their existing bikes to the younger set, or develop new products that appeal them instead, they are in danger of becoming the Oldsmobile or Buick of the category, tagged as the bikes for the “mature” side of the marketplace. Oldsmobile is extinct and Buick has lost about 40% of its sales in the last several years. In 2009 Harley introduced its first three-wheel model in more than 30 years, the Tri-Glide Ultra Classic, further evidence that it sees its audience is turning a bit gimpy in the saddle.

Harley does own the Buell sub-brand, which makes smaller, less expensive sport bikes aimed at the younger market. But that brand has competed with only marginal effectiveness against the import brands. Japanese bikes still hold over 90% market share in the category.

The Harley Davidson brand is so strong, that it actually makes an estimated five percent of its revenue from licensing the trademark for merchandise and other items. That’s huge. People who will never own a bike proudly wear Harley shirts, hats, and belt buckles. Ford even offered a Harley Davidson edition of their F-150 pickup for a time.

Locally, the Harley brand has even become part of the York County brand. In recent years, York has positioned themselves as the “Factory Tour Capital of the World.” A key centerpiece to that promise is the tour of the Harley Plant on Route 30. Harley lovers from around the country rumble into town just to see it. It’s a huge draw for the county and a place that its residents are proud to work for.

Harley knows its equities and nurtures their unique qualities. Through far worse times than these, they’ve been able to invigorate their products and rebuild their base. They’ve done a terrific job of staying true their brand and not branching out into ill-fitting categories for the sake of keeping revenue growing but at the expense of their chrome plated image.

But as with much of the American manufacturing industry, they are facing hard choices to stay competitive and effective in their marketplace. It seems fairly certain that Boomers will continue to buy the big bikes until their knee replacements make it impossible to hold them up at traffic lights. But how Harley chooses to develop the brand for Gen Y and younger markets will determine their success in next 20 years.