Cyclists are putting pressure on rail company Govia to allow more space for bikes on trains.
Govia will take over the South Central rail franchise to run most Sussex trains from current operator Connex.
Govia proposes a fleet of new trains with only two spaces for bikes. The space would be shared with wheelchairs and bulky luggage.
Dave Witts, a member of Brighton campaign group Bricycles and the Cyclists' Touring Club, said: "These trains can be redesigned.
"We must make sure Govia takes note of what cyclists need. We shall be using these trains for about 20 years."
Cyclists say about ten spaces are needed on each train. They have been backed by many MPs and councils.
Pavilion MP David Lepper has written to the Strategic Rail Authority calling for it to hold a meeting with cyclists.
The SRA has the power to order train operators to put more space for bikes on trains.
Bricycles is urging members to write to Govia, the SRA and the Rail Passengers Committee for Southern England.
Mr Witts said cyclists were also urging proper space for wheelchairs, pushchairs and bulky luggage.
They also want Govia to carry bikes at peak hours so that cyclists can commute by train.
Govia curently runs the Thameslink franchise, which allows limited space on trains for bikes. The company has said it will consult cycling groups.
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