Would larger tires hurt mpg's

[euromodder]

Wider tyres create more drag, mechanical and aerodynamic, even if they may have a lower rolling resistance coefficient.

4cm wider is a lot.
As tyres are virtually never mounted straight, they're always scrubbing a bit. The wider they are, the more scrub (and drag) you'll have.

RRc is measured perfectly straight, which is rare in real life .
Some ecomodders have set wheel toes to 0° to effectively reduce fuel consumption - and take the reduced stability in stride.

[serialk11r]

Wider will at least increase drag, but taller? I'd guess that the slight increase in drag is offset by the lower engine rpm, but the difference is going to be really small compared to any change you make in gearing, well, in the driveline.