MIAMI -- Drivers heading down to the Florida Keys this weekend may see a lot of spandex on the highway.

On Friday morning, almost 300 bicyclists and a few hundred support volunteers headed off on a 165-mile journey to Key West.

The group is riding to raise money for HIV and AIDS charities. So far, the cyclists have raised more than $500,000.

“Over 50 percent have never ridden a bike this far, but they’ve been training for months,” said organizer David Spacht.

The riders will do 100 miles on Friday, heading south from Pinecrest then over the Card Sound Highway. From there they will head south on U.S. 1 and spend the night as Hawks Cay Resort.

On Saturday, they will ride another 65 miles, arriving in Key West Saturday afternoon.

They will be riding single file so as not to block traffic.

Many of the riders said they are participating in the event, now in its fifth year, for deeply personal reasons.

David Gendal put together a five-man team called “Keith’s Kickers” in honor of the brother he lost 14 years ago to AIDS.

Gendal's childhood friends from California and Utah came to South Florida to pedal for the cause.

Kathleen Frezza, who has participated in the ride three times, told Local 10’s Kellie Butler that Mother Nature can make or break the grueling trip.

“There have been years where I’ve had a headwind the entire way. That was difficult. Other years I’ve had a tailwind. That’s what we’re hoping for today," she said.