IT'S HARD taking instructions on how to ride a mountain bike up a 10,000ft (3,000m) peak from somebody who used to live in Calais. Only the Netherlands can have fewer hills than the Pas de Calais departement. Climbing lessons from a vertigo sufferer would be more convincing.

Eliane Wissocq left the Channel port for Crested Butte in Colorado a decade ago. Now, in the oxygen-starved but rose-tinted atmosphere of the quaint old mining town, she helps to run a week-long festival of mountain-biking, a celebration of the knobbly-tyred contraptions that have rejuvenated the world's cycle industry and turned city streets across the globe into imaginary mountainsides.

America invented the mountain bike when Californians began turning old delivery bikes into lumbering off-roaders guaranteed to build leg muscles bigger than Daley Thompson's. Now Europe and Asia have perfected them, milling frames from space-age materials and churning them out in numbers that car companies could only dream about.

Eliane is caught between the Rockies and a hard place, but comfortably. She loves America, but is pleased that the worldwide growth of mountain-biking is supplying her with a steady stream of Europeans and Japanese eager to spend their holiday time, like hundreds of Americans, panting up and down Mount Crested Butte on organised tours, learning how to fix that troublesome 20th gear in maintenance classes or trick cycling around the town's recently paved and gingerbread-housed main street.

The car has never really featured in Crested Butte. It is as if Henry Ford put a black line around the place when he invaded the rest of the US. Horses made the town. Saloon bars such as Kochevars still boast hitching posts, and the bijou bars and bakeries that make up for the Crested Butte's lack of a real grocery store are fronted by the hitching posts' modern equivalent, bicycle racks. Dayglo Diamond Backs and Treks are lined up like greys and piebalds, while their saddle-sore owners visit the shops.

Crested Butte owes its Fat Tire Festival to the fragility of the male ego, says Kat Peterson, its organiser. 'Motorcyclists from ritzy Aspen, just over the next peak, used to ride here across the treacherous and often snow- clogged Pearl Pass, and steal away the town's maidens,' she claims. (Ms Peterson is a Crested Butte maiden herself.) Boozers in the Grubstake bar on Elk Street responded by paying the girls of Aspen a visit, travelling on converted single-geared paper-boy bikes. The journey of revenge became a race, and the race a festival. Motorbikers are still frowned upon in the Butte.

Sixty people turned up for the first event in 1980. This year, more than 300 rode into town for the 13th Fat Tire Bike Week, some in family groups on bikes with three seats, some world-class racers riding machines costing more than pounds 2,000.

You can spot the out-of-towners on Elk Street. They pant even when walking from one store to another. It takes 10 days to acclimatise from sea level and a month to forget the altitude completely, but in the meantime it is easier to appreciate a glass of the locally brewed Fat Tire Amber Ale or Rustlers Gulch red wine.

The serious cyclists, however, are more inclined to head into one of half a dozen bike shops than the Idle Spur bar or Le Bosquet bistro - and since a new tyre costs pounds 17, and a new suspension pounds 150, their entertainment budgets have to be restricted.

The mining heritage of the town serves the mountain bikers well. 'I've biked a lot of places,' Eliane Wissocq said. 'But the mining history here has given us a lot of great tracks to ride. There is a real variety, although it is a bit hard for a beginner.'

'Beginner' in Crested Butte doesn't mean novice, first-timer or rookie. Not if the beginner's ride I took is anything to go by. 'The pace is going to be slow,' Eliane warned. Fine. 'But going up hill you'll know you are not at sea level.' Er, OK. I was a real beginner: it had taken my friend Nathan Bilow, a photographer from Colorado, to get me to break a 10-year habit of driving everywhere. 'Crested Butte's beautiful in summer, and the riding will be great,' he promised

The Trek racing team offered me a bike for the ride. It weighed less than my trainers but cost more than a suite at the Savoy. It could go anywhere its rider could. In my case, being 10 years out of the saddle, not far. To save my backside from the skimpy saddle, there were front and rear shock absorbers.

A million people a year take up mountain-biking in the US. A million people older, larger and less fit than me. I stopped whining and joined the Lycra-shorted wannabees.

'This will be a real booger-blower,' said Steve, our instructor, referring to the contents of our noses. Larry Kranig, from Wisconsin, was more worried about his ticker. 'I only have one lung, so I have to keep my pulse down,' he said. I stuck with Larry, so inspiring was his willpower.

Patri Yamashita, a teacher from Hawaii, made it a threesome. 'If I don't finish, can I buy your notes?' she inquired. Her brother is a 'bike-head', a mountain bike fanatic. She was here to keep him company. We were the only real beginners, and it showed.

With the first hill came the first pain. My lungs felt like lead weights. I looked across to Larry. He was pedalling faster with only one lung. I gritted my teeth and took deeper breaths. 'My brain says go, my body says no,' screamed Patri from behind, grinding to a halt on the narrow mountain path. Julie Andrews would have felt at home here, but these hills were alive only with the sound of pain. Weeds and wildflowers choked the spokes and pedals, but Larry and I kept going. Whatever the professionals earn, it is not enough.

The Fat Tire Bike Week was beginning to feel like a masochists' seminar. If another self-righteous biker said 'no pain, no gain' once more, I would have gone in search of the nearest Harley Davidson convention. Luckily, some mountain bikers like a laugh. To them, the bicycle is a circus tool, perfect for bicycle polo or performing tricks. And with not a hill in sight.

Lou Gonzalez is the godfather of bicycle polo. In a deep Cuban-American drawl, he explained the basics of the game. 'My wife is really to blame. We were playing a slow game of croquet in 1987, so she got on her mountain bike and started whacking the balls around.' In fact, like real polo, the bicycle variety originated in the Indian subcontinent, and the Maharajah of Punjab has invited Gonzalez and his pretentiously named World Bicycle Polo Federation to visit India for a series of matches.

Polo has been part of the Fat Tire Bike Week for five years, played on the local high school sports ground. 'It only takes 45 minutes to an hour to learn, then we split people in teams,' Lou said. 'Each match is then split into two 10-minute chukkas.' As Lou got the first match of the week off to a start, mad cyclists wielded mallets above their heads, cars pulled over and a crowd formed. Cheers filled the air. It made a nice change from the pain.

In the festival headquarters up at Crested Butte Mountain Resort, Larry wandered by the noticeboard, glancing briefly to see what else he could sign up for. Apart from the daily rides into the Rockies, Fat Tire Bike Week offers a variety of events in the village itself - not just polo but also bike repair classes, medical conferences and trick cycling competitions. The rodeo sounded a bit iffy: riding up over a car wasn't really Larry's idea of fun. The chainless bike race, freewheeling down a slippery mountain road was more his forte. He initialled the form.

Andrew, his 10-year-old son, pedalled up to his dad. The pair started riding together after Larry lost a lung. 'A 16-year-old might be embarrassed by a 42-year-old dad wearing tight pants,' Larry said. 'But Andrew's cool. We rollerblade together as well.' The rest of the family were off hiking and having lunch.

As you may have guessed, Fat Tire Bike Week lasts seven days. The first three or four are, loosely, recreational. But for the final weekend, things get serious, and the festival hosts a round of the top mountain-bike championship in the US. I didn't stick around: the sight of professionals whizzing where I had been wheezing would only have added to the pain.

Fat Tyre Bike Week is held annually, normally in the second week of July. Contact PO Box 782, Crested Butte, CO 81224, USA. Telephone: 0101 303 349 6817. Registration costs up to dollars 60. Individual races or bicycle polo costs from dollars 15 to dollars 50.

Accommodation in Crested Butte varies from bed and breakfast for about dollars 25 a night to the four-star Grand Butte Hotel where rooms start at dollars 75. Self-catering apartments start at dollars 59 a night for four to six people. Contact Crested Butte Vacations (fax 0101 303 349 2397) or the US Travel and Tourism Administration in London (071-495 4336).

Continental and United Airlines fly into nearby Gunnison airport via Denver. Airlines normally carry bicycles free (within baggage allowance); pedals must be removed and handlebars aligned with the frame.

(Photographs and map omitted)