Harley owners come not just from all 50 states in the Union, but from all over the globe to attend this celebration of American engineering. On the wall of Rally HQ, at the top of Main Street, is a map of the world, where visitors mark their point of departure with a coloured pin. It is not unusual to find three dozen pins in Switzerland, the same number scattered across Scandinavia, and a couple each in Sydney and Hong Kong. Some die- hard Harley devotees have their bikes flown from Asia into Los Angeles, where they will pick them up and ride over the Rockies and across the plains. Others come annually from as far away as Rio, Lima and Buenos Aires, often taking weeks to complete the trip. As well as celebration, there is an undoubted sense of pilgrimage: for Harley owners Sturgis is Ascot, Glastonbury and Mecca rolled into one.
Sturgis during rally weekend is not the world's prettiest sight. For a start there's a preponderance of balding, bearded, sunburned, middle- aged white men with huge, hairy beerguts spilling out of their black leather waistcoats and over their jeans. Some are Hell's Angels, others just common or garden gross-outs. The more ridiculous among them scrape their grey hair into ponytails, held in place with surfer-style wraparound sunglasses.
Typically, they also sport blurry tattoos of eagles, suck on endless cans of Budweiser, and wear T-shirts with provocative slogans: "If you don't limp you ain't shit" and "I love cats - they taste just like chicken" are two of my favourites, and who could fail to love: "Beer - it's not just for breakfast anymore"? Sadly, one is just as likely to encounter the far less amusing: "If I'd known they'd be this much trouble I'd have picked my own damn cotton." Black people do attend the Sturgis rally - it's just that there aren't very many of them. Last time I counted two. One was on a Fat Boy Harley, the other was flipping burgers.
Wander the backstreets and you'll stumble across fringe groups like the Christian Motorcyclists Association, born-again Harley owners who like to gather in parking lots for Bible classes, and whose Hogs typically have an airbrushed crucifixion scene on the tank, with a slogan along the lines of "It was not the nails that held Christ to the cross but his love for you and me".
Sturgis also attracts a small percentage of senior citizens, many of whom have sunk their life savings into a "fully dressed" Electra Glide, Harley's huge touring motorcycle, complete with panniers, fairing, heated seats, and a remarkably good hi-fi. On such machines they embark on their final tour, cruising down the highway into that last golden sunset.
Of course, the biggest section is made up of those Harley heads who just want to belong, to go and sink a few beers at the Broken Spoke with fellow enthusiasts and discuss the relative merits of Knucklehead, Panhead, Shovelhead and Evolution engines.
The link between them is a passion bordering on the maniacal, a curious conflation of patriotism, consumerist conformity, and notions of individual freedom that we have learned to call the American Way.
But what is it that inspires such devotion, such fanatical identification? After all, Harleys are not the cheapest or easiest of machines to maintain. On both my visits to Sturgis, even ardent Hog-owners advised me that a basic knowledge of mechanics and a good tool kit were indispensable for anyone thinking of touring on anything other than a brand new Harley.
Clearly, any lack of consistency is more than compensated for in aesthetic terms. Most owners will rhapsodise interminably about the engine's sound - a fat, throaty rumble with a slightly laid-back quality. Others will tell you it's the shape of the tear-drop petrol tank, or the feathery quality of the suspension on a Softail, or just the sheer amount of gleaming chrome "bolt-ons" that can be added to the basic machine. There is a huge industry in Harley parts, with dozens of firms making all kinds of compatible spares, from chrome handlegrips with grinning skulls at each end, to stainless-steel custom forks - essential for coastal riders who would otherwise be continually cleaning rust off their chrome surfaces.
Indeed, it is the customising industry that has made Harley-Davidson the legend it is today, and saved it from the vagaries of fashion to which most forms of transport are normally subject. Customising allows Harley- Davidson constantly to reinvent itself, and thus to be all things to all people. Unlike the machine itself, perhaps, the plan is simple and works perfectly. The company makes a limited range of models, suitable for touring, sports and urban use, which it promotes as American classics, the metallic manifestation of the democratic ideal. This encourages Harley riders to see themselves as rugged, independent, free-wheeling individualists, the last true cowboys, blazing a trail across God's country on their 80-cubic-inch steeds.
But this is just the basic conceptual model, the "factory spec" framework onto which each owner can then bolt his own personal tastes and preferences. Colour and imagery of paintwork, chrome spares, engine size, height of frame, quality of suspension, type of wheels, guards, pedals, handlebars and lights - all these become ways of changing the shape and size of the bike, the riding position and the "meaning" of a particular Harley-Davidson. Perhaps the most obvious indication of this is the seat. Some bikes, like the FXR low-riders, often have a generous passenger pillion with a "sissy bar" backrest. Others, particularly heavily customised Fat Boys with slick pastel paint jobs and lots of chrome, have only the meanest little stump of upholstered leather perched on the rear wheelguard - obviously there's no way such a machine could take two people, this is strictly a loner's bike.
The book and exhibition, The Art of the Harley, gives an insight into this aspect of America's psyche, and shows how those with a good enough credit rating can commission their own personal work of art - which they can then ride around the country. The last time I was at Sturgis I naively asked a professional customiser, a Floridian called Larry, what in his opinion was "the right way" to customise a Harley-Davidson. He looked at me blankly for a second. "This is America," he said. "There is no right way. If you got the money, your way is the right way. Anyway you want it."
! 'The Art of the Harley' is a new book (Booth-Clibborn Editions, pounds 19.95) and an exhibition, starting Thursday at the Barbican Art Gallery, London EC2.Reuse content