You've probably heard of Burning Man and Bonnaroo. But you might not be familiar with RAGBRAI: the world's largest and oldest bike tour, improbably located in Iowa, that arguably serves as the quintessential summer festival of the Midwest.

Instead of covering themselves in body paint, RAGBRAI riders don spandex jerseys with pun-inspired team names. Instead of dropping acid and making art, they throw hay bales, listen to Journey, and drink cans of Bud Light given away by friendly locals. RAGBRAI is an idiosyncratic mix of extreme exercise, alcohol-fueled revelry, and Midwestern kitsch: By day three, you're used to seeing middle-aged moms take shots of Fireball at 10 am, just after riding 30 miles and before buying ham balls to support a church fundraiser.

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Last week, I joined more than 15,000 bicyclists for this year's 462.2-mile ride across Iowa, officially called the Register's Annual Great Bicycle Ride Across Iowa. We weren't pedaling across endless cornfields in 90-degree heat to race, or to raise money for charity, but solely for the fun of it — and for the opportunity to make frequent stops in small towns for pork chops, pie, and cold beer.

Despite all the incongruities you see during RAGBRAI, though, the strangest aspect of the ride might be its hidden history. This outsize Iowan tradition was essentially started by accident by a pair of newspaper reporters 42 years ago.

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Two reporters' impromptu 1973 ride across Iowa

The first ride occurred when a copy editor at the Des Moines Register, John Karras, challenged columnist Donald Kaul to ride his bike across the state and write about it. Kaul insisted that Karras come along, and they invited readers to join. Or at least that's RAGBRAI's official story.

In reality, their motivation was a bit sneakier. As Smithsonian magazine's Megan Gambino wrote in 2009, they wanted to go on a bike trip and get the paper to cover their expenses. Editors accepted the idea, but told them to invite readers. "I wrote a little story, about six inches maybe," Karras told Gambino. "Donald Kaul and I had this incredibly stupid idea to ride across the state and anybody who wanted to come with us was welcome to do that."

They expected a handful of teenagers at most. But about 300 riders turned up on the morning of August 26, ready to ride. As they made their way across the state, bemused farmers and town residents offered them food and water. The reporters stayed in motel rooms, typing up stories and dictating them over the phone, while the others mostly camped on motel lawns.

By the end, 114 people had made it across the state, and the columns Kaul and Karras had filed fascinated many more. These pieces profiled eccentric riders such as Clarence Pickard — an 83-year-old who hadn't biked since childhood and wore long underwear and a pith helmet in the heat. Afterward, the writers got letters asking them to organize another ride the next summer, which led to SAGBRAI: the Second Annual Great Bicycle Ride Across Iowa.

How RAGBRAI became the world's largest bike tour

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SAGBRAI was much larger and more well-organized than the previous year. The Register provided trucks to carry riders' luggage during the day, as well as a van to pick them up if they were unable to finish. The ride began with 3,000 people, and 1,700 finished.

These numbers convinced Register staff to establish the ride as an annual event — and stick the paper's name in its title. Over the next few years, planners began establishing the traditions that define the ride today: varying the route from year to year, having riders dip their tires in the Missouri River at the start and the Mississippi River at the end, and including an optional 100-mile day somewhere in the middle.

And the ride swelled dramatically, with tens of thousands of riders crossing the state annually by the '80s. One key reason was economics.

Having this many bikers flood a small town might sound like a traffic-snarling mess. But early on, Iowa's increasingly depopulated rural towns realized that being a RAGBRAI stop — or, better yet, hosting riders overnight — was a rare chance to make money from out-of-town cyclists with large appetites. As the ride grew, cities and towns began vying for the chance to serve as a host, competing to provide the best campgrounds, entertainment, and hospitality.

Nowadays, the route is packed with vendors selling food, beer, and supplies, both in towns and in the cornfields between. Churches, schools, and fire departments across the state sell pie for fundraisers. Host communities prepare for weeks, and most residents take the day off to work booths in matching T-shirts bearing mottos of local pride.

Over and over, restaurant and shop employees I met told me that the day we passed through was their busiest day ever — approached only by the previous time RAGBRAI came through five years ago. In 2008, it was calculated that RAGBRAI brought $25 million to the state, a number that's likely grown in the years since.

Why thousands of people ride across Iowa year after year

About two-thirds of RAGBRAI participants are repeat riders, and the enthusiasm of communities along the way is one of the big factors that draw them back to Iowa. While plenty of people do unorganized bike tours on their own or participate in similar rides that have popped up in many other states, RAGBRAI is the oldest and has snowballed into the largest by far.

Ride officials cap the number of week-long riders at 10,000, but thousands more ride for a day or two or do the whole thing without registering. On some days of last week's ride, police counted as many as 19,000 cyclists. All this means there are plenty of shuttles that will bring you and your bike to Iowa from major cities, and that it's never hard to find food or water. If you want to do a bike tour, RAGBRAI has become one of the easiest ways to do it.

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But even more importantly — and despite its huge size — RAGBRAI has retained the same flavor of informality and eccentricity that defined the early rides. It's not free, but compared to, say, concert festivals or marathons, it's relatively inexpensive: $160 buys you a week of camping, daily transportation for your luggage, and support vehicles. It also has a decidedly less corporate feel than many other events, as most vendors are local businesses.

And while it's a fairly intense athletic endeavor — you're biking at least 60 or so miles a day for a week straight, after all — it never quite feels that way. Unlike a triathlon, there are no times or medals. Instead, towns host hay-bale-throwing contests, and people with houses along the route offer up their pools for hundreds of sweaty cyclists, while giving away lemonade or beer.

Some teams of riders go back decades. They live apart during the year, then get together every summer to ride specially outfitted, garishly painted buses to Iowa and reminisce about the "Soggy Monday" of 1981 or the "Saggy Thursday" of 1995.

I'm not an old-timer, but this year was my second RAGBRAI: I first did it in 2013. And during this return, a friend and fellow rider came up with a good analogy that captures the surprising allure of riding across Iowa with thousands of other people. RAGBRAI is a bubble in which you're allowed to talk to strangers, dress like an idiot, and spend all day outside instead of sitting behind a desk. In essence, it's summer camp for adults who like to bike.

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