swathdiver
Full Access Member
Of course GM knows, but it’s a range. Where on the range they end up claiming I.e. 70% of the “real max” or 75%, etc depends on other policies in place for claiming/advertising these types of numbers, and that involves independent testing.
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There are now standardized tests by the Society of Automotive Engineers, the J-2807. The Big 3 all adhere to them now. This is one reason GM went to such huge grills, to increase the ability to shed heat while towing.