The American Cancer Society's Bridge to the Beach event got underway in the pouring rain.
It started at the base of the Ben Franklin Bridge and will end at Bader Field in Atlantic City.
It's a 66-mile journey to raise money for cancer research.
"We're not going to let this weather stop us. The fight against cancer is not easy, and neither is this, and so we're here in the rain, it doesn't matter," says Paula Green, Vice President of ACS Philadelphia.
The ride is in its 50th year and in that time it has raised $30 million for cancer research.
Organizers say some of today's riders have taken part in all 50 of the rides.