Like travelling with a precocious child or pedigree puppy, travel with a Harley and bystanders can’t help but come over for a stroke and a coo. But with vast green-tipped cornfields and distant, towering silos flanking the open road ahead we are reluctant to stop.After a few hours on the Softail, however, my own tail is anything but soft. Road-worn, windswept but feeling undeniably cool we stop at the Ariston caf?Litchfield. Though decommissioned in the 1970s you can still follow the brown and white Route 66 Heritage Highway plaques that indicate where to jump off the main Interstate (highway 55) on to what remains of the old Mother Road and its roadside attractions. Centuries later but before the advent of the multi-lane American highway, Route 66 replaced the dirt tracks, a 2,381-mile road connecting Chicago to Santa Monica.Since its inception in 1926, the adventures of the open road and American popular culture have been nowhere better embodied than Route 66 – “the mother road”. We scoot over the Mississippi river casting a glance at the old Chain Rocks Bridge, Route 66’s original river crossing. Gateway Arch is St Louis’ monument to the American West, where wagon-train pioneers paved the way for Route 66 with a dusty frontier road stretching from Missouri to California.

Harley-Davidson is the motoring equivalent of a Tuvan throat singer; you can’t believe all that noise is coming from one set of tubes. Burning out of St Louis it would be nice to say that we confirmed the tourist-board tag that there’s “more to St Louis than the arch” but once on the highway with the exhaust pipe rumbling contentedly there was no stopping us. Like cheerleader chants and slide guitars it is pure acoustic Americana. Sit on the back of one, however, and the characteristic combination of rumbling vibrations means that for the first half-hour you’re constantly looking behind you for a chapter of Hell’s Angels. But for the moment, as we finally get our motor running and head out on the highway, the only thing I am thinking about is how to contain an enormous yelp of idiot glee. High-fives and whoops of “Yee-haw” may be uniquely American, but girly squeals, I suspect, aren’t that credible in die-hard biker country.The most distinctive thing about a Harley is its noise.

We eventually manage to make a diplomatic shift to the 250lb lighter Heritage Softail, which unlike the Ultra Classic (complete with intercom system, stereo and more padded leather seating than a three-piece suite) is a bike that according to manager Matt Surdyke “you can really feel the road on” As my rear end would latter attest he was not lying. I fidget with endless racks of Hog merchandise – biker boots, biker jewellery, biker underwear – and wonder on what occasion a pet dog would require a miniature leather biker’s cap embossed with the company logo. Out on the forecourt I’m greeted with a sharp reminder that despite its merchandising muscle Harley-Davidson is still as much about the bike as it is about the brand. My companion is test-driving our nominated rental, the Electra Glide Ultra Classic, at 850lb the biggest motorcycle that Harley-Davidson has ever made and, for the uninitiated, no easy rider.Monster trucks scream past us on the nearby highway and my designated driver begins to look more Woody Allen than Dennis Hopper. Surrounded by the kind of men whose bulk is complemented by nearly half a ton of bike it seems rather emasculating to suggest my companion might be more comfortable astride something a little smaller. The plan: to travel the eastern end of Route 66, into the heartland of the Harley-Davidson Owners Group, or Hog.As a consummate pillion passenger, I couldn’t care less about gas tanks and the complexities of Harley’s heel-toe manipulated gear shifter. This epic two-wheel tour, dubbed “The Ride Home”, is being billed as the biggest American road trip ever planned.Earlier we had picked up a rental bike several hundred miles south of Milwaukee, at the Surdyke dealership near St Louis, Missouri, to make our own ride home.

To celebrate the centenary, 250,000 bikers from as far afield as Barcelona, Tokyo and Sydney will arrive in Milwaukee, the final stop on their pilgrimage to the birthplace of the bike. With several hundred miles of highway still ringing in our ears, the silence is oddly deafening. Sitting in a quiet roadside caf?n Water Street it’s hard to imagine Milwaukee as the host of the “world’s largest rolling birthday celebration”. On a muggy evening in mid-August dark dock houses loom over the recently regenerated canal-side area of this modest Mid-West city, the new waterside walkways as deserted as the surrounding concrete shopping precincts.