Bad Mileage 4.8i Sport Wheels. PSI Problem?

[youry]

Originally Posted by bawareca

My results are not scientific, but I have seen people here report over 500 miles on a full tank. I was never able to get over 450 miles even with soft driving style. My mileage varies very little from city to hwy. Doing 80 on the hwy is where the roll resistance will have most impact so it makes sense.

I get 500+ miles per tank(highway), 2012 X35i 56k, still running the original/factory Bridgestone RFT dueler tires (factory 18" wheels)

[macmac80210]

Originally Posted by youry

I get 500+ miles per tank(highway), 2012 X35i 56k, still running the original/factory Bridgestone RFT dueler tires (factory 18" wheels)

Tire size probably makes a huge difference, and you're also running a '12 3.5 and I'm running a '07 4.8.

I am now sitting right around 9.5 MPG after 2 tankfuls and a solid mixed-city commute. I have brand new Bridgestone tires, so I don't think that should be the issue. I have been trying to milk the mileage, but it's just not coming. I think the real issue is increased lb/ft of torque required at startup from 0mph because of the larger wheels. I was coming from a pair of 17" with a winter Bridgestone setup, and it's just frightening to see a 5+ MPG decrease with these things.

Any ideas on who to talk to about shitty mileage? Dealer or some tire place?