Major automakers are scrambling to strip hundreds of kilograms off future pick-up trucks to meet coming US standards for fuel economy without sacrificing strength or towing capability.The new mandates will take effect in 2016, giving automakers such as Ford and General Motors just one design cycle to make significant changes that will require costly steel substitutes such as aluminium, new steel alloys and magnesium.Automakers are faced with having to pass on those higher costs to buyers who have come to associate mass with performance.Dick Schultz, an expert in the use of metals in autos, said: "There is a lot of hand-wringing in the industry right now. You can't afford to be on the wrong side of this thing."CORPORATE AVERAGESAutomakers must reach an average fleet fuel economy of 6.6 litres/100kmbby 2016. Light trucks - which were half of all US auto sales in the first 11 months of 2010 - will have to get about 7.8 litres/100km.The US corporate average fuel economy (CAFE) standard for 2010 is 8.1 litres/100km. For light trucks alone, it is 9.4 litres/100km, according to government data.The updated standards come at a time when auto companies are launching an array of electric plug-in and hybrid vehicles which will help the sector reach those new goals but reducing the weight of their trucks is also vital to meeting the guidelines, automakers say.This represents a significant challenge because of the trucks' large size and the demand that they be able to handle heavy loads and towing in unforgiving conditions.Current pickups weigh an average of nearly 2300kg. BOWING TO DEMAND: Most buyers expect their bakkies to be able to tow over great distances and handle heavy loads with ease. To entice consumers, automakers have added comfort, electronic and safety features over the past decade. As a result, the weight of trucks has jumped 22 percent from 2000 to 2010, federal data shows, while fuel consumption rose only two percent.The first US automaker out with a new-model large bakkie aiming to comply with the tougher fuel economy standards will be GM with its Chevy Silverado for the 2014 model year. Rick Spina, who leads full-size truck development for GM, said: "It's a tough task but we're facing it as grown-ups. We're going to do everything we can to keep the customer from realising we've had to make changes in a fundamental way."In addition to the 2016 target, automakers may have to achieve CAFE standards of 3.8 litres/100km for the overall fleet by 2025, less than the most ambitious scenario outlined by the US government.COST OF SHEDDING WEIGHTSpina said GM wanted to shed nearly 230kg from its trucks by 2016 and by the early 2020s might need to cut as much as 450kg per truck. Using blown-in foam instead of a cheaper, but heavier, pad to buffer noise in certain areas of the vehicle could become more common, Spina said.Meanwhile, Ford is looking closely at a magnesium alloy frame for the next generation of its F-150 bakkies, two people familiar with the matter said. Ford is also looking to use aluminium for the F-150 shell, they said. By moving away from traditional steel, Ford could shave about 360kg off a truck, one person said. The comments were made privately because the information is not yet public.Ford declined to comment on its specific product plans but its global product development chief Derrick Kuzak told Reuters Ford has been aiming to trim as much as 318kg from its vehicles under a target it has previously made public. Ford's F-Series is the No.1-selling vehicle in the US, followed by GM's Silverado.GM is also exploring the use of aluminum and magnesium for the bodies of future models of its Silverado and GMC Sierra trucks, Spina told Reuters.CHANGE IS COMINGAutomakers are starting to tout fuel economy as part of the brawny image of trucks but past advances in vehicle engineering, including the use of lighter materials, have proved hard to sell to buyers.Eric Fedewa, IHS Automotive director of global powertrain forecasting, said the additional costs could squeeze the truck market's sales."With fuel economy standards where they are, trucks are going to get kind of edged out of the top of the market," Fedewa said. "Everything is going to change in the next vehicle cycles."