Usually, squeaking significant extra mileage out of a vehicle involves some very conspicuous changes. You can switch to a new engine, go hybrid (or full electric), or build components out of lightweight materials like carbon fiber. GM, however, is trying something different with the just-launched 2017 GMC Acadia: glue. Rather than join the SUV's underbody components using rivets or welds, GM is using aircraft-grade adhesives along the seams to create a body so stiff that the company can afford to use thinner steel. The result is an Acadia that's a whopping 700 pounds lighter than its predecessor, giving it 23 miles per gallon (versus the 2016 model's 18) without having to resort to more drastic changes.