Jana Partners, the activist hedge fund, reported a 14.8% stake in Titan International ( TWI), a wheel and tire manufacturer that is in the process of being taken private. In a filing with the Securities and Exchange Commission, Jana criticized an offer made by One Equity Partners to buy Titan for $18 a share in cash, saying the price is "well below the true value of the company." In a letter attached to the filing to Titan CEO Maurice Taylor, Barry Rosenstein, Jana's founder, said that he raised his stake to protect an existing investment and block the acquisition. The stock closed Monday at $18.12, up 4.1%. Still, the stock is up about 36% from its $13.28 closing price on Oct. 11, when Titan announced that it had received the buyout offer. In his letter, Rosenstein criticizes not just the proposed price but the process Titan is using to negotiate. He says that the company has failed to describe the steps it has taken or will be taking "to ensure a full and open biding process" for itself. He says $18 represents "significantly less than fair value." Among other things, Rosenstein says the offer price doesn't reflect the value of Titan's acquisition of the Goodyear agricultural tire business, which is supposed to close in February. One Equity Partners is a private equity affiliate of J.P. Morgan Chase ( JPM). It manages $5 billion of investments and commitments for JP Morgan in direct private equity transactions. A call to a Titan spokeswoman was not returned.