Handled internally, 15 firms were initially invited to participate, though 13 went forward into the formal review, which began in January.
Incumbent firm Cohn & Wolfe, which has worked on the Michelin task since 2005, is defending the account.
Mann said that the decision to possibly seek out another firm was prompted by the company's occasional assessment of whether an agency was the "best fit and focus" for the division.
The process is tentatively set to finish in April, with the winner starting work in early May.
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