The ride-hailing giant disclosed this morning that its I.P.O. could value it at $91 billion — less than what it had told some investors to expect a few weeks ago. Uber set a price range of $44 to $50 for its stock sale, leading to a valuation of $80 billion to $91 billion. It had mentioned a figure of $100 billion to some bond investors, and some bankers had suggested it shoot for $120 billion. This might be a Lyft effect.