Reason for sudden gas mileage change?

Yep changes it a lot. I was a smog tech in Cali and you can see if the difference in emissions too with the gas. They change the blends to help with pollution and what not different times of the year and different states have more or less regulations for the gas and what additives go into it and change your mpg. I went from Cali getting 18 or mpg to Az at about 19-20mpg to Utah getting 22mpg and Colorado getting around 18 again.

 

My mileage has gone up this winter after having new rims that were actually lighter than stock rims. I thought this might be due to better aerodynamics. Has anyone else experienced this?