Pittsburgh has a well-deserved reputation as a quirky city.

From its unique “Yinzer” accent, to its peculiar culinary delights (french fries on sandwiches and salads?), to its hard-to-fathom roadways that to outsiders resemble less a grid than a plate of spaghetti, that quirkiness is part of its charm.

And recently, a spectacle that had long been a quiet, underground bicycle event has begun to capture attention for the city well beyond its borders and expand on its singular appeal.

The Dirty Dozen bike race, held on the Saturday after Thanksgiving for most of the past 32 years (the day changed in the early years), challenges cyclists to race to — or simply reach — the top of 13 of the toughest hills in Pittsburgh and several border suburbs. The 33rd annual ride took place Saturday, covering a mostly leisurely 55 miles but ascending a lung-searing, thigh-burning 5,000 feet on the hills.

Over the past five years, the race’s unique challenge has gotten the attention of the national and even international biking community. But that attention has grown the field so large so quickly — 328 competed last year, 230 on a rainy day this year — that it threatens to undermine one of the race’s central tenets.

“It’s a ride for anyone who wants to do it,” said Danny Chew, the quirky race’s equally quirky manager for the past 32 years and the person given the bulk of the credit for making it an iconic city event. “Cyclists who are just trying to finish can ride with nationally ranked cyclists.”

Relying on a volunteer crew of marshals who hold back cars at key intersections, Chew and his distinctive, high-pitched, warbly voice have led the increasingly large field around the city’s narrow streets all these decades without ever taking out permits with the local governments through whose borders he passes.

The race has gotten large enough that some of its biggest fans, including Chew’s family and friends, worry it may have to change to continue to keep it safe.

“I’m concerned if it gets much bigger,” said Chris Helbling, 48, a mechanical engineer and the race’s head marshal. “Should there be a format change to separate the racers from the riders? I don’t know. But it’s been discussed.”

The weather shrunk the field this year, but the number of participants was still more than the race ever had until five years ago. In deference to the discussions about safety and the size of the field, this year for the first time Chew agreed to send the “racers,” who try to earn event points, ahead of the rest of the field on two particularly congested hills.

If it doesn’t sound so tough — how bad could a ride in a city in the foothills of the Appalachians be, right? — one must experience some of these streets that were carved out of the sides of river valley hills in the 1800s to fully understand.

One of them, Hill No. 9 — Canton Avenue — in Pittsburgh’s Beechview neighborhood is so steep, at a 37 percent grade, that the city contends it may well be the steepest paved urban street in the world. Though No. 9 is only about 150 yards long, a good chunk of the field fails to get to the top without walking its bikes up the cobblestone surface, resulting in the spectacle of cyclists falling sideways as they attack it. It typically attracts the biggest crowd of any of the hills, as it did Saturday.

Jennifer Aker, 29, drove in Saturday morning from Columbus, Ohio, with two friends and, like many before her, found Canton Avenue unconquerable.

She gave it one go and found herself at a dead stop about one-third of the way up the hill, falling to her left into a spectator, who was not injured. One try was enough.

“I didn’t want to hurt anyone else,” she said of her decision not to attempt Canton again.

Maybe because of all of that pain caused by such hills, the race attracted just several dozen riders a year for its first 22 years. Most of those were friends of the five founding riders — Chew; his older brother, Tom; and three friends — who started the race in 1983 as a way to get in a tough training ride on the worst hills.

But then early social media latched hold of it in 2006, pushing its field over 100 for the first time. In 2010, local Pittsburgh public television documentarian Rick Sebak at WQED got a tip that he should do an episode on the Dirty Dozen.

It didn’t take Sebak much time to figure out why.

“It’s one of those things I love about Pittsburgh: It’s kind of goofy, and it was just so brilliant that that they came up with that kind of event,” he said. “It celebrates the city and the topography without being too obvious, I guess. It’s something that could only happen here.”

After the video got linked to cycling Web sites around the country, its impact on the race was immediate.

The race nearly doubled in size, to 305 riders in 2011, and grew a bit more last year to set a new record with 328.

Despite all of that, the race remains, at least so far, as grassroots as possible. It still is not advertised. There are no racer numbers to identify riders; racers are credited with “points” for finishing first through 10th simply by calling out their names to spotters at the top of each hill. The start and finish lines are sometimes marked with chalk, or simply by someone standing at the appointed mark.

That grassroots feel and the challenge were what first-time riders said drew them to Pittsburgh the Saturday of a holiday weekend to ride through six hours of pain.

“I saw this two years ago on the Internet and I thought, ‘Man, this is crazy. I want to do this,’ ” said Dustin Dinh, 42, a dentist from Austin who spent three days driving the 1,400 miles to Pittsburgh for his first crack at the race. “It was on my bucket list.”

But by the end of the six hours of hill-climbing, it was two local riders who took top honors.

Steve “Stevo” Cummings, who had won the race 10 straight times until last year, regained his crown Saturday, outpointing a field many thought was the most competitive in the race’s history.

Cummings, 35, a real estate agent from Pittsburgh, says every year he isn’t sure if he’s coming back and said this time: “No. I think I’m done for real.” Other racers said no one believes him.

The women’s winner made her own history.

Stefanie Sydlik, 30, a former U.S. national team rower and an assistant professor of chemistry at Carnegie Mellon University, won the race going away in her first attempt. She also became the first woman in the race’s history to finish in the top 10 overall on a hill, taking fifth place on the last.

“I want to go home and die now,” Sydlik, exhausted, told Chew as he congratulated her on her win and she rested on her bike. “It was harder than I thought.”

It’s a phrase uttered by every first-time rider of the Dirty Dozen, and probably will be for as long as the race is held — just the way Chew and his fellow co-founders had hoped in 1983.