I can't for sure say that the winter tires help mpg, but I do know I don't see any difference between all season and winter tires in what concerns mpg. It is true though, that we didn't have any snow yet. They say it will be for tomorrow within 5-8 cm mark.
White Platinum Metallic Tri-Coat
303A, 6-Speed SelectShift Automatic, 17" Aluminum wheels, Luxury Package,
Parking Technology, Navigation, Winter Package
Chevy Volt 2014, White Diamond, Luxury Package, S1, Navigation.