Reduced MPG w/ New Tires & Belt Replaced

[Johnny Outback]

I have a 2009 Outback Limited w/ 58K miles, original owner. I replaced the OE Bridgestone tires with Bridgestone Turanza Serenity Plus tires from Costco. I spoke with Bridgestone and these tires were HIGHLY recommended for my car. I also had the drive (not the timing) belt(s) replaced.

Since this work has been done, I have observed a reduction of approximately 6 - 8 miles per gallon, especially with highway driving, over the past 1K miles.

The car also seems to be working harder to get it moving.

Any thoughts, similar experiences, etc...?

[147_Grain]

A taller tire might throw the MPG off. Also, height and width of tires vary from each manufacture, even though the tire size (numbers) are the same.

Winter fuel, or buying low-grade fuel can also affect MPG, as can LOWER air pressure in the tires.

[Radar]

Check tire pressure first. Some change in mileage would be normal, but that seems like a lot. Perhaps the tire change happened around the same time winter gas formulation hit the pumps?

Tire design is a series of compromises between handling, wet traction, dry traction, snow traction, braking, mileage, lifespan, etc. Improve one thing and something else isn't as good. Maybe these tires excel at things that tend to compromise mileage.

[grossgary]

that kind of loss is very excessive and abnormal, something is definitely wrong if those numbers are accurate.

if you suspect a large drag on the vehicle...it sounds like you do...this would be a great excuse for a cheap and fun tool: an infrared temperature gun, you can hit both sides of the hubs/rotors through the wheel spokes and compare to the other side - one side significantly higher than the other suggests a dragging brake. the temps are highly variable and so you'll need to take a few readings per side to get a trend/compare, but it'll be obvious otherwise. neat tool to have for auto/home/play, they're often on sale or cheaper elsewhere, $20 on amazon:
Non-Contact Infrared Laser Thermometer

or - jack up each wheel and rotate the tire by hand to see if a caliper is hanging. fronts are most likely. use emergency brake to hold vehicle while doing fronts in neutral and emergecy brake must be off to rotate the rears - so use a lift or brace the front wheels/vehicle appropriately.

or just have a shop do it.

you're sure it's not allowing the car to warm up while de-icing, snowing, cold, etc?