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Much has been made of the Cadillac ATS's aluminum underpinnings: extensive use of the lightweight metal has helped give Caddy's new compact luxury sedan a curb weight that undercuts the Audi A4, BMW 3-series, and Mercedes-Benz C-Class. But one particular drivetrain component on the CTS reveals why aluminum isn't always the best solution for fuel efficiency.
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The ATS's rear differential is, counterintuitively, constructed of cast iron. Why such a heavy metal? After an internal study which lasted several months, Cadillac engineers determined that the fuel economy gained by using a cast iron differential outweighed the benefits of going with aluminum. Due to the thermal expansion properties of aluminum, which have a detrimental effect on bearing friction (not to mention the NVH losses due to the whines and whirs the aluminum unit produced when heated up), engineers decided that the added weight of cast iron was a worthwhile tradeoff for the downsides of the lighter metal.
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Ken Kelzer, Cadillac's Global Vehicle Chief Engineer, says "Considering the gains in fuel economy and NVH, we decided we'll take the mass hit in this case and find it someplace else."?
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