Drastic gas mileage difference?

[Brandonw91314]

I have a 2010 CX-7 Sport automatic. It came with the OEM 17 inch wheels. I recently purchased and put on the OEM grand touring 19 inch wheels. I have noticed a dramatic decrease in my gas mileage. Does the grand touring have different gearing or what would cause this change? I thought since they were OEM wheels and tires there wouldn't be a huge difference.