Americans - like their cars - are getting heavier every year. Unfortunately, it seems the tested passenger capacities of the cars they drive are not keeping up. Two-seaters like the Mazda MX-5 and the Chevy Corvette aren't rated to carry two 200lb (91kg) adults - and some, like the Cadillac XLR are just barely rated to carry an average American couple, reports USA Today.

It's not just sporty coupes and roadsters that can't handle the increased girth of their grocery-getting governors. Minivans (or MPVs), SUVs/crossovers, and sedans are all skimping on approved passenger weights. Examples include Acura's TSX, which seats five people, as long as their average weight doesn't exceed 170lb (77kg), and Mazda's CX-7, which sports identical specifications.

Auto makers claim the weight limits are based on a mandatory federal formula that only allots 150lbs (68kg) for each passenger - a number which is clearly unrealistic for the average American. The Centers for Disease Control (CDC) determined in 2004 the average American man weighs 190lb (86kg), while his female counterpart weighs 163lb (74kg).

While all of the cars involved can carry more weight than their ratings show, as Honda spokesperson Sage Marie says, automakers "can't be responsible for the vehicle's dynamic characteristics" if the maximum passenger weight is exceeded. Manufacturers reportedly build in a safety margin, though how much is unclear and likely varies between makes and models.

The bottom line: American bums are crossing the line between unhealthy and unsafe.