What measurements do I look at when buying new rims?

What I'd do is plug your car in at TireRack website, see what it comes up with. Be forewarned, pretty much any rim is going to need adapter rings, to bridge the gap between the vehicle's hub protrusion and the hole in the alloy. That's the way with any of the one-size-fits-all aftermarket alloy rims.

If you want to know the specific data, you can likely find it, or "reverse engineer" , by looking at the data of the rims TireRack suggests.

 

Size of the rim, width of the rim, offset.

Size is the simple 16" or 16" stuff.

Width is the difference between the edges of the rim and determines the width of the tire.

Offset is important because it determines if the rim will clear the brakes. Think of it as how far out or in from the center of the wheel the hub is.

 

For MPG purpose I would keep it close to stock as possible. Another thing to consider is the cost of buying new tires as apposed as to keeping the stock ones for your new wheels. Like me I decided to keep the stock 16 to save money and they fir my new wheels just fine. Wheel weight for gas mileage purposes the lower the better! I went with a little wider rim then stock and kept the stock tires. MPG is around 48. Not to bad!!!