Size and weight are a big part of GM’s DNA. They beat Ford not with a frontal assault on the Model T but by offering a larger, heavier, flashier car. They thought they could do the same to BMW. But, even as the Bavarians packed on the inches and pounds, car buyers “in the know” saw the additional size and weight of Cadillacs as a sign that the General either lacked technical competence or just didn’t “get it.” Well, maybe the “new GM” really is different. With the 2013 Cadillac ATS, the company has pulled out all the stops to directly challenge the BMW 3-Series with a rear-wheel-drive car that is—surprise—a few tenths of an inch smaller and a few pounds lighter. Could the people who tried to sell us the Cimmaron have gotten this one right?