New fuel-economy rules coming down the pike are likely to displease pretty much everyone, if a public hearing held Monday is any indication. In the current proposal from the National Highway Traffic Safety Administration, auto manufacturers must achieve a fleet-wide average fuel economy of at least 31.6 miles per gallon by 2015 — a jump from 25 mpg today, and a step toward Congress’ target of at least 35 mpg by 2020. But Big Auto, shaken by the shaky economy, has backed off its previous support for the standards. Ford’s CEO laments a lack of “adequate resources or lead time”; Toyota now says the proposed regulations are “substantially front-loaded”; and the Alliance for Automobile Manufacturers says the timeline isn’t “technologically feasible” or “economically practicable.” (The comments are aimed at the 2015 timeline; manufacturers say they continue to support reaching 35 mpg by 2020.) For their part, greens say the proposal is too lax, noting that NHTSA’s calculations unrealistically assume that gas will be $2.25 a gallon in 2015.