Robin Chard, 48, from Bicester, suffered a cardiac arrest after about 25 miles (40km) in Sunday's cycling event and died in hospital.
He hoped to raise £400 for Cancer Research UK but funds have hit £50,000.
Andrea Day, 43, said the family was "very touched by the kind messages".
"As you can imagine, we are all very shocked and saddened by the news of his passing," she said.
"He was a beloved son, husband, father, brother and friend to so many and will be sorely missed."
Mr Chard was taking part in the 100-mile (160km) event as a "personal crusade" after his father and stepfather died from lung cancer.
He himself had survived Hodgkin Lymphoma as a child.
Ed Aspel, executive director of fundraising at Cancer Research UK, said: "We are very grateful that he chose to cycle in RideLondon to support Cancer Research UK, and would like to express our deepest sympathy to his loved ones at this difficult time."
RideLondon said Mr Chard suffered a cardiac arrest at Kingston Bridge "and although he received immediate treatment from fellow riders and medical personnel at the scene, he died later in Kingston Hospital".
More than 29,000 riders took part in the event. Of these, 33 were taken to hospital, three had serious injuries, the organisers said.
What is RideLondon?
The sister of a man who died in the RideLondon event after surviving cancer as a child has said the family is "touched" after a huge spike in donations towards his charity appeal.