I don't know much about art, but I know how to bike

While mainly associated with Hell's Angels, 'Easy Rider' and the endless open road, the Harley-Davidson motorcycle has also been a platform for wild creativity, as Serena Mackesy discovers at the Barbican.

One generation's radicalism is the next generation's retrospective. Peter Fonda will be 59 this year and Dennis Hopper 63, the same age at which Lee Marvin died in 1987. Marlon Brando, 74 in 1998, long since handed over the torch of rebellion to his troubled children. And, as the generation inspired by The Wild Ones (1956) and Easy Rider (1969) contemplate bus passes and dialysis, the Barbican Art Gallery is mounting "The Art Of The Harley" (opening today), dedicated to the cultural influence of a motorbike-manufacturing enterprise started by a pair of schoolfriends in a Milwaukee shed in 1903.

However narrow your definition of art, this is a delightful exhibition, one of those collections of human ingenuity and eccentricity that leave your heart lighter. Across a window, skeletally sparkling, a selection of wheels, cogs and exhausts surround the building of another artwork that will continue throughout the exhibition. "Soft rooms" feature displays on the biker tribes, photos of mental-health workers covered in tattoos of screaming skulls, and a chance to tap into the website of the Alaska Ladies' Harley-Davidson Club (who, for obvious reasons, don't get to meet up much). And then, laid out along a "road" and gathered outside a "roadside diner" are 30 of America and Europe's best customised Harley-Davidsons, most only recognisable as being related by the presence of that familiar, airplane-style headlamp.

The habit of customising first became really noticeable among young servicemen demobbed after World War Two (but the original "Hell's Angels" were actually WWI fighter pilots in a 1930 Howard Hughes film of that name). Restless after their adventures, they formed ironically named gangs (the Gypsy Jokers, the Booze Fighters, Satan's Slaves) and rode about the West Coast, thumbing their noses at the establishment. When a clash with the American Motorcycle Association ended in riots in Hollister, California, in 1947, the gangs made Time magazine. The film producer Stanley Kramer decided the incident would make a good movie, and The Wild One, in which good- guy Brando rides a Triumph and bad-guy Lee Marvin straddles a Harley, was born. A succession of US and European bike-exploitation movies followed: Roger Corman's hysterical Motor Psycho, These Are the Damned (with Oliver Reed gorgeous in black), Scorpio Rising, The Leather Boys (an early gay movie), All the Fallen Angels (an early triumph for Peter Fonda) and the laughable The Glory Stompers, which provided a break for the ever-hammy Hopper. When Fonda and Hopper teamed up for the much-admired Easy Rider, the Harley's synonymity with liberty, bohemianism and everything that was not redneck was set in stone.

A replica of Fonda's "Captain America" bike - stars-and-stripes fuel tank, ape-hanger handlebars, sissy-bar at back - graces the entrance to the Barbican show. Compared with later boy-toys, it's small potatoes. The works of Arlen Ness, Tank Ewischek and colleagues are so barking as to often hardly resemble motorbikes at all: a chopper almost entirely enclosed in flame-covered metal looks remarkably like a burning goat; black-leather fringing on another brings splutters of delight; there's "Flamed Shovel" in shocking pink with flying jelly beans, and "Miami Nice", in powder blue, covered in palm trees. Pride of place, though, goes to Ness's mad "Two Bad", a concoction of chrome and gold with exhaust pipes so curly they'd not be out of place in a waterpark. It's beautiful in the way a Heath Robinson is beautiful: you couldn't imagine it actually working.

The pull of the custom Harley is wrapped up in the gradual demise of the American Dream - not so much financial abundance as personal freedom and the chance to be a rugged individual. During the post-war consumer boom, the pioneer spirit became an outmoded anachronism as the grandchildren of emigres settled into tract houses and exchanged their souls for security. Cars and bikes, those symbols of mobility, took on a ferocious symbolism for those who still clung to the dream of independence: in modern America, the equivalent of the horse and gun of 150 years ago.

The grand irony is that, in the 1980s, Harley nearly killed the market in choppers by producing their own assembly-line special editions such as the "Wide Glide", a move that suddenly brought into focus that, rugged individual or not, the Easy Rider generation had, after all, been supporting yet another giant corporation. There is no doubt, though, that the exhibits here are things of beauty, exemplars of the human urge to stamp individuality on a homogenised world.