If the new-car market is a Big Mac, full-size sedans would amount to only the sesame seeds. They're a sliver of the auto market, accounting for just 3.5% of new-car sales in the first seven months of 2013. Still, automakers believe in big cars. Seldom does a comparison see so many redesigned or new entrants. From April 2012 to April 2013, four new or redesigned full-size sedans hit dealerships. Through the first seven months of 2013, those four nameplates accounted for nearly half of full-size sedan sales.