DETROIT, MI -- All summer long, a massive horde of bicyclists rode through Detroit's streets on a weekly basis, halting traffic and filling neighborhoods with an unusual sight every Monday night.

The crowd keeps growing, with city residents, suburbanites, avid bikers and people who haven't been on two wheels in decades joining the 12- to 15-mile ride they call Slow Roll.

Some bystanders during the most recent outing jumped and shouted with amazement at the size of the horde. Others appeared annoyed by the effect on traffic, but couldn't seem to take their eyes off the seemingly endless lines of riders pouring through the streets.

It was a flowing river of helmets, funny hats, baskets, honking horns, bells, reflectors and mounted stereos of all kinds.

There were racing bikes, road bikes, mountain bikes,flashy custom bikes, Walmart bikes, cruisers, low riders and one absurdly tall, yellow bike.

Detroit's Slow Roll group bike ride 5 Gallery: Detroit's Slow Roll group bike ride

"We are quickly becoming the largest group bike ride in the country," said Mike MacKool of Detroit Bike City, who leads the riders.

The group takes a new route each week, rolling through different neighborhoods at 8-12 mph.

The group's reach has spread through social media and word-of-mouth.

Lisa-Jane Sanfield of Berkley and Allison Feiler of Huntington Woods joined in for the first time this week.

"I just want to check out what’s new in the city," said Sanfield, 42. “You’re going down streets that you wouldn’t normally go down by yourself.

Feiler, 38, said it was the first time she mounted a bike in some 30 years.

"I’m just hoping not to fall down and kill myself," she said.

Feiler survived.

There are only a couple Monday's left in the Slow Roll season. Next Monday's ride will have a prom night theme.

More information on joining the group here.

Follow MLive Detroit reporter Khalil AlHajal on Twitter @DetroitKhalil or on Facebook at Detroit Khalil. He can be reached at kalhajal@mlive.com or 313-643-0527.