Yeah, I find it pretty silly, too. There used to be extended range fuel tank options on some vehicles, but they've largely gone away. I believe some tests are d

Yeah, I find it pretty silly, too. There used to be extended range fuel tank options on some vehicles, but they've largely gone away. I believe some tests are done with x% of fuel on board, so of course a larger tank will mean a greater curb weight, lower fuel economy, etc. Ultimately I think it's more about an unintended side effect of regulation than it is about true market forces. On the other hand, we have to assume the average fuel tank load is <50%, so a larger tank truly DOES end up resulting in a heavier vehicle and lower fuel economy on average. We'd all get better mileage if we ran tiny fuel tanks and fueled our cars every day.