This weekend, thousands of cyclists will gather, strip naked and ride through the city. At this point, few in Portland are oblivious - the city knows the Naked Bike Ride is back.

The World Naked Bike Ride - officially a worldwide protest against dependency on oil, for cyclist safety and in support of body positivity - has grown enormously, from a giggling get-together to the city's biggest and best-known event.

What gets lost in the record-smashing numbers of bare naked cyclists is the why and the how: Why in the world are these people doing it, and how in the world did it take over Portland?

Firm answers are flimsy, but the history laid bare shows a story of passion, anarchy and a union of warring factions. It's an evolution from old Portland into new, from a local protest into a globally-recognized event. And the future, as sunny as it seems, is wrought with worry over what the ride has become and what it will be.

Few events have had such a profound impact on Portland, but then again, few events are quite like the World Naked Bike Ride.

The 2015 World Naked Bike Ride in Portland.

Critical Mass

The story of the World Naked Bike Ride starts with Critical Mass.

Like the Naked Bike Ride, Critical Mass was a massive gathering of urban cyclists, riding en masse to bring attention to bike safety. The two events also shared a decentralized organization; Critical Mass was a monthly event that took place in cities around the world, each with little to no structure to speak of.

Cyclists called it a protest. Police called it anarchy.

The tension bubbled over in 2002, when Portland Police officers used pepper spray and a stun gun as they arrested nine people and issued 47 citations to participants. After that, crowds of up to 2,000 became the norm, setting up regular clashes with police.

"I think there was a question as to whether or not at that time police in Portland really cared about safety of people on the road including people riding bikes," Carl Larson, a longtime volunteer with the World Naked Bike, explained. "Whatever happened, it became not something that was really fun to go to."

As Critical Mass flamed out in Portland, one of the offshoot events in the cycling scene gained steam.

The official first year of the World Naked Bike Ride in Portland was 2004. It was a fairly small gathering, drawing about 125 people to the streets. In the early years, the ride was sandwiched between pre- and post-ride parties. People didn't take off until midnight, and they didn't take off their clothes until it was time to ride. It wasn't about nudity, it was about the protest - and having a good time.

"Portland loved a good event," organizer Meghan Sinnott remembered.

But soon the scene began to change and the crowds grew. Suddenly, 125 friends turned into 170, then 450, then 800, then 2,000. Estimates from the first few years are rough (and have been a point of contention), but organizers knew the ride was quickly growing out of control.

By 2008, the year the crowd topped 2,000, the city's patience began to grow thin. Sinnott, who was on the ride for the first time that year, remembers pulling off to block traffic at the intersection of West Burnside Street and Southwest Broadway. After waiting too long to let cyclists pass, a driver of pickup truck began to inch forward, not deterred by Sinnott's presence. It started to push her out of the way, encroaching into the crowd.

"I was just shocked," she said. "Really, I'm a naked lady with glasses on in the middle of the street, I don't know how much more ridiculous or vulnerable I could be right now."

A fellow volunteer helped get Sinnott out of the way, losing his bike under the truck in the process. The incident had a big impact on the riders, but the city took notice too. The World Naked Bike Ride had grown too big for its own good, and it was time for the police to step in.

Making peace

Bret Barnum remembers how Portland police felt when the World Naked Bike Ride began: It wasn't positive. He was a traffic officer when it started in 2004, and said the police bureau's approach mirrored that of Critical Mass: enforce the law.

But there was little they could do. Since 1985, Oregon law has held firm that public nudity is allowed as long as it's a form of protest. The World Naked Bike Ride has always been a protest, so police allowed it to go on. Their biggest problem was not getting a heads up, of getting caught off guard.

For years it was a cat-and-mouse game between participants and police, but once the ride grew to thousands it was impossible to keep the game going.

"We recognized that the police were going to get involved no matter what," Larson said. "We said we might as well make some kind of effort to direct this thing in some positive way."

Sure enough, after the 2008 ride, the Portland Police Bureau approached organizers of the ride, asking them in to meet about the future. There was hesitation, Larson said. Some cyclists were uncertain about working with the cops. Who knew what would come of collaboration?

But the reality was far different. Police were tired of fighting with cyclists. Cyclists were tired of fighting with police. By 2008, the Critical Mass rides had dwindled to 15 people a month, and the era of bike anarchy was fading into the past.

"As the police bureau has evolved over the years we've become much more accommodating, we've seen things in a different light," Barnum explained. Then, the question had become, "how do we as police kind of act as mediators and make it safe for Naked Bike Ride folks, and make it safe for the public?"

Both parties put the past aside and found compromise - an amazing feat in a world still bristling with law enforcement conflict, where World Naked Bike Rides in other cities can still lead to mass arrests.

Their deal was this: Portland police would block off traffic and offer a motorcade for the ride, if the Naked Bike Ride organizers agreed to run the route by city officials and cut back on the pre-ride drinking.

If there was grumbling on either side of the table, it faded fast - it was ultimately an easy decision to make.

"It's thanks to the Portland Police that this has been possible," Sinnott said. "It was such a revelation that it's not us against them."

As it turns out, the assistance was necessary. That summer the ride grew again, from 2,000 to 5,000 riders. In 2010 it grew to 7,000, with some organizers reporting a crowd as big as 13,000 people. The numbers were rough, but one thing was official: Portland's World Naked Bike Ride was the biggest in the world.

Mainstream nudity

By 2013, the year the ride celebrated 10 years in Portland, the city had changed a lot from the days of Critical Mass.

A younger generation was moving in. Housing prices were on the rise. "Portlandia" was on the air and gentrification was the new cause du jour. Taking part in the ride had become less a potent protest and more a rite of passage.

Numbers had dipped the two years prior, but by 2013 - the first year with an official head count - it was back to a record high: 8,150 riders strong. The next year it hit 10,000 and in 2015 it plateaued at 10,100 riders, no longer a ragtag group of bike activists but a diverse population of cyclists young and old, professional and amateur, some there to protest and others there to party.

Longtime organizers appreciate the popularity, but as the 13th ride approaches this year, they express a newfound anxiety of what the World Naked Bike Ride has become.

Chief among their concerns? The image of the ride. As the event has grown, the fact that it's a protest has become lost on the public - participants included. In 2015, organizers began to press the issue, selling stickers that promoted each of the ride's three primary causes.

For the former Critical Mass protesters who started the ride, it's been disheartening to see the point missed. Several longtime organizers spoke out in support of highlighting the protest message, though some were more understanding of the cultural shift.

"It's an organic event that happened and it's going to change with the city of Portland," Jason Wurster, a former organizer, said. "I think the onus is on the organizers to get that messaging across."

As local residents and city officials relax, a new schism appears to be rising within the ride's ranks. Some echo those protest concerns, but a few are more worried about other evolving aspects of the event, like the lack of post-ride party.

"You don't expect the anti-war protesters to have a party after," Sinnott said of the complaints. "Are we an organization that plans parties, or are we an organization that plans protests?"

But even as that philosophical quandary bubbles, the World Naked Bike Ride faces a much bigger issue: size. All the growth has been exciting, but both organizers and police admit that the event can't get much bigger.

As it stands, it takes about 40 Portland police officers to manage the event. Earlier this year the short-handed bureau announced it was cutting back staffing on events, and while the World Naked Bike Ride is immune it might not be for long.

"If the event decides to just triple in size it will be an event that I fear personally will become confrontational," Barnum said. "We don't want to tell them 'no,' because we know 'no' means anarchy, 'no' means 'we're going to do it anyway.'"

It means sacrificing that well-tendered relationship and maybe going back to the days of Critical Mass. Of citations and arrests. Of pepper spray and stun guns. Organizers get it, and they're taking measures to scale back.

For the 2016 ride they chose Mt. Scott Park, a lesser-known location much deeper into southeast Portland. The hope is that fewer people will make the trek out, keeping the ranks steady for another year. It runs contrary to the message of strength in numbers, but as far as they're concerned, they have numbers enough.

"We're the largest ride in the world and we never meant to be," Sinnott said. "10,000 is a really awesome number, we don't need any more."

But how big the ride grows is not up to organizers or police - that's something only Portland can decide. As the uninitiated continue to ask why, people will show up on their bikes in the buff, bellowing a rally cry that has overtaken the ride: Why not?

--Jamie Hale | jhale@oregonian.com | @HaleJamesB