 The first riders left Clapham Common at 0600 BST on Sunday |
About 27,000 cyclists have put pedal power to the test to ride the 56 miles from London to the Brighton seafront. The 28th British Heart Foundation London to Brighton Bike Ride on Sunday will raise an estimated �2m for the charity.
The first riders left Clapham Common, in south London, at 0600 BST and began converging on Brighton from 0930 BST.
Most people take an average of seven hours to complete the route.
Foundation spokeswoman Saffron Garner said: "It is a beautiful day here - hot and sunny. It always seems to be sunny for the London to Brighton.
 The event started in 1976 when 30 friends rode from Hyde Park |
"When it's hot like this it's probably a bit more exhausting but it's preferable to riding in the rain."
Among the riders were people on tandem bicycles and some in fancy dress - including a pair who wore Batman and Robin costumes and a team in Star Trek outfits.
One 60-year-old man invited 60 friends to join him and rode a bicycle which belonged to his daughter when she was aged six, Ms Garner said.
Surrey Police said one rider had suffered facial injuries when he fell from his bike just south of the M25, in South Mersham, Surrey.
The event started in 1976, when about 30 friends cycled from Hyde Park in London to Brighton.
Last year, the ride raised �2.45m for charity.