elements would be measured . It had to be lightweight , strong , and durable . With respect to weight , the team evaluated the latest advancements in high alloy structural steel and chose Nucor steel with its high strengthto-weight ratio . The Frontrunner is the first and only bus in its class to incorporate a purpose-built chassis manufactured in the U . S . utilizing American-made Nucor steel . Characterized by having a strengthto-weight ratio four times that of cold rolled steel , its ability to flex under load makes for a more comfortable ride and is far less likely to crack than traditional cold rolled steel that becomes stiff and brittle as its gauge is thickened . Frontrunner ’ s innovative approach was to remove the frame rails of the cutaway completely , replacing them with a purpose-built low-floor structure . The new lowered floor chassis fits precisely in the openings of the original frame rails , another industry first , transforming a cutaway into a purpose-built low floor mini-bus . To address the corrosion issue that plagues the cutaway bus market , the Frontrunner lowered floor chassis incorporates a “ hot-dipped ” galvanization process considered to be the most superior form of corrosion resistance available , yet another industry first . The Frontrunner ’ s entire low floor chassis is dipped into an 800-degree bath of molten zinc . At that temperature , the pores of the steel open and are permeated with zinc . This unique process allows the treated steel to self-heal . If an object abrades the steel , the zinc in the pores of the steel will self-heal as the zinc is exposed to the air . This process makes undercoating unnecessary on the Frontrunner . The Frontrunner ’ s fully composite bus structure , awarded three patents for its strong yet lightweight design , incorporates pultruded beams in the composite side wall panels for impact protection and additional strength around the windows and main bus door . Pultruded beams are a composite material yielding the same strength as traditional steel , with only 25 percent of the weight . It is corrosion free and is frequently used in high strength-to-weight applications , including bridge structures . Its ability to bend but not break adds to its strength and durability . The modified sandwich panel wall construction also has a high R-value – keeping the bus cool in hot weather , and warm in cold weather . Frontrunner Bus Group was also the first to introduce a fully composite sub-floor in a low floor cutaway sized bus . Guaranteed for life against water penetration , rotting , swelling , and mildew , the sub-floor is another example of a component that meets the criteria for strength , weight , and durability . “ It is generally accepted that , regardless of traditional undercoating , plywood sub-floors rot over time ," LaRose added .
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