[FirstSubie]

On my 2011 Outback at 40K miles, I decided to swap out the ContiContact OEM tires. They were pretty good for OEM, but I have always been a Michelin man on everything that rolls, so I went with the Defender. Even with 3 extra pounds of air pressure, I have lost 2-3 MPG on a familiar Interstate over the old Conti's. Has anyone else had this experience and how did you resolve it?

 

[Soledad]

I'm not sure how to solve it but I did do some quick checking and find that the Defenders are about 2 pounds heavier and have a few rev's less per mile than the Conti's. Is that enough to make a difference? I really have no clue. One would think it wouldn't but maybe it does.

We had a 2009 4-cyl Hyundai Sonata that was getting phenomenal fuel mileage on the stock OEM tires from about 7k miles thru 60k miles. When they wore out we switched over to another tire that was exactly the same size and type and almost immediately noticed that we had lost a few mpg's as well as some power. And as those tires wore we never regained the awesome gas mileage that we once had before finally trading the car in.

 

[Looby]

Possibly just a slight increase in tire diameter? That would make the
odometer indicate less mileage for the same distance. It would look
like a reduction in mpg, when it's only a change in odometer accuracy.

 

[there4igraham]

The rolling resistance could be different as well. If the Defenders have a more radical tread pattern it could result in a decrease in fuel mileage.

 

[cardoc]

With Michelins, the X series are the better tires for comfort, noise, wear and fuel economy.

A couple things I noticed in the post are an increase in diameter and air pressure. When you increase air pressure, and there is not a load on the tire, the center of the tire will bow out, increasing the diameter more. Slight changes in the diameter and contact effect the overall fuel economy.

Did the fuel economy change right away, or has it been a few thousand miles since you last checked? Meaning, did you keep a constant rating record with every fill up, and did it change immediately after the new tires?

Reasoning: Other factors may be involved besides and aggressive tire and rubber compound. Alignment for instance. First one is due by 30-40k miles. Misalignment causes more frictional force on the wheel. Type of fuel used. We are in to winter blends which will effect fuel economy greatly. Temperature, both ambient and the engine temperature effect the performance of the engine. Colder temps = more fuel usage. And the same can be said about the temperature of the tire itself. Electrical loads. Heater, defrost, heated seats, heated wipers, heated mirrors, etc., change engine loads to a higher percentage.

Winter brings on higher fuel demand from the vehicles, especially the fuel. Switch to high octane fuel and see if it changes.

 

[FirstSubie]

Defenders

Thanks for the replies. I had the alignment done (it was only slightly out on one front, one back) and the mileage dropped immediately after the tire swap using the "door jam" air pressure. I generally like to run a bit more air than stock, so I jacked it up a couple pounds to see if it made a difference-nope. I am driving the same 275 mile trip I drive once or twice a month, so it's not a difference in track, fuel formulation, load weight or anything I can lay my hands on that has changed, other than the skins.

I don't think two pounds of unsprung weight per tire can drop the mileage by 10%+, nor do I think the slight change in diameter could account for it either. I am stumped, but if this is as good as it gets, I am going to let NTB have them back on their 30 day ride guarantee and go back to what I know worked (at $30 less per tire)... Very disappointed-last time I switch to Mickeys, I gained about the same I have lost this time...

Any other theories out there?

With Michelins, the X series are the better tires for comfort, noise, wear and fuel economy.

A couple things I noticed in the post are an increase in diameter and air pressure. When you increase air pressure, and there is not a load on the tire, the center of the tire will bow out, increasing the diameter more. Slight changes in the diameter and contact effect the overall fuel economy.

Did the fuel economy change right away, or has it been a few thousand miles since you last checked? Meaning, did you keep a constant rating record with every fill up, and did it change immediately after the new tires?

Reasoning: Other factors may be involved besides and aggressive tire and rubber compound. Alignment for instance. First one is due by 30-40k miles. Misalignment causes more frictional force on the wheel. Type of fuel used. We are in to winter blends which will effect fuel economy greatly. Temperature, both ambient and the engine temperature effect the performance of the engine. Colder temps = more fuel usage. And the same can be said about the temperature of the tire itself. Electrical loads. Heater, defrost, heated seats, heated wipers, heated mirrors, etc., change engine loads to a higher percentage.

Winter brings on higher fuel demand from the vehicles, especially the fuel. Switch to high octane fuel and see if it changes.

 

[4wheeldog]

You say that the fuel formulation has not changed.......I do not know where you live, but winter fuel everywhere makes about a 10% difference in mileage, for me. This, along with cold, driving with headlights one etc could account for the difference, and the seasonal change just happens to coincide with the tire swap.