Cyclists renewed calls for the introduction of more cycle-friendly trains as thousands of riders prepared for Sunday's London-to-Brighton race.
Riders relaxing on the beach after the London to Brighton ride
About 27,000 cyclists take part in the annual ride but, since 2004 train operators have refused to take riders to and from the start and finish.
"There will be absolute chaos on the roads, as there is every year," said Ian Davey of charity Bike For Life.
Southern Trains said new rolling stock meant it could not accommodate bikes.
The London-to-Brighton ride, which began in 1980 and has raised over £3.6m, is always full long before the day of the event.
The decision to ban all bikes, including folding cycles, on Sunday prompted calls for the government to introduce cycle-friendly rules for train operators.
David Holladay, of the Cyclists' Touring Club (CTC), said a Government White Paper, due to be published shortly, should address the inflexibility of some trains.
"We want to see trains capable of having their seats flipped up during events like the bike ride in order to carry bicycles," he said.
Mr Davey said his Brighton-based organisation believed it was absurd that people would have to drive to London to take part in the race.
A Southern Trains spokesman said: "When we had the old slam-door trains we used to be able to accommodate up to 50 bicycles in the guard's van but that is not possible with the new rolling stock."
The British Heart Foundation, which organises the 54-mile ride, said a special "truck and bus" service had been run since 2004 to take bikes to and from Brighton by lorry.
"We are continuing to offer the service for registered riders between London and Brighton to ensure participants can continue to take part," said a spokeswoman.