A study by the RAC Foundation says the vehicles can carry people in larger numbers and there "is no evidence to suggest that the thousands of users of the bendy bus would prefer to revert to a double-decker".
Taking them out of service in favour of lower-capacity buses, it maintains "will increase volumes on the busy routes with a reduction in journey speed".
The mayor's transport adviser Kulveer Ranger described the report as misjudged and misdirected. However, Labour's London Assembly transport spokeswoman Val Shawcross called on Johnson to reassess his decision.
"The mayor should pay close attention to this report, which reflects public concern. The legacy of Johnson's wrong-headed transport policies could be higher fares, more congestion and longer waits," she said.
The report is available at PlanningResource.co.uk/doc