WHEN NEW PRODUCTS AND CUSTOMER LOYALTY COLLIDE

''Why did you mess with a good thing? There are enough fad shoes on th e market already. We never thought you would sell out. '' Another angr y letter, this one from a former marathon winner and long-time loyal c ustomer. Henry Carson had thought it was time for his company, Pacer A thletic Shoes, to upgrade its standard offerings for the serious runne r and expand into walking shoes. But after investing considerable reso urces in the effort, he's having second thoughts: the returns so far a ren't good; old customers seem confused or, worse, annoyed; Pacer does n't seem to be attracting many new customers, despite a flashy marketi ng campaign; and the company has had trouble getting its manufacturing up to speed. A mid-pack marathoner in the 1970s, Henry started Pacer to serve runners like himself. Back then, he thought of himself as an entrepreneur with a mission, not as a corporate empire builder. But Pa cer grew along with the market, and in 1991, Henry had to admit that h e was no longer an entrepreneur. Instead, he was running a $10 million corporation and facing decisions he had never anticipated. Industry s tatistics, along with a customer profile, seemed to indicate that Pace r was vulnerable to attacks from much larger competitors. As far as He nry could determine, the company had been left with no choice. It had to upgrade its offerings and build a following in the broader market s o that if the industry giants did attack his niche, Pacer could surviv e. Henry thought he had taken steps to give Pacer staying power. What went wrong? Five experts offer their views on Pacer's current options.