Problems with new tires
 

I recently got new tires, and was excited to get an increase in gas mileage due to buying LRR tires, however, the opposite has occurred. I have lost a solid 10-15% in gas mileage since changing tires, and I'm curious if there are any suggestions to what could be the problem. I went from Goodyear Assurance Tripletreads to Michelin HydroEdge with Green X in the same size. The Michelin's were supposed to be much lower rolling resistance. It has gotten colder, but I have a scangauge, and I can't even get as high of mpg when the car is warmed up. And all my locations where I mentally marked to start coasting are no longer valid and I have to drive past them before I can coast, so I'm pretty sure there is some extra resistance, and it doesn't have to do with the engine.

I haven't gotten my alignment done yet and will try to do that tomorrow, but could that really be knocking off so much mileage? The alignment was good with the old tires too, so I wouldn't think it would be too bad with new tires. Thoughts? Thanks :)

Well, the cold, no matter if the car is warm or not will lower mileage a fair amount. This would be my guess as to what the main culprit of the worse mileage is.

Second, new tires have a higher rolling resistance than old worn tires. As your new tire breaks in, the mileage will increase.

1) All other things being equal, a new tire will consume more fuel than a worn out one. More mass, particulatly more mass in the tread area = more fuel consumption.

2) There is a technology tradeoff for tread rubber compound between treadwear, traction, and fuel economy. In your case, you went from a 740/A/B to an 800/A/B. In some respects that indicates the wrong direction for fuel economy. Further, your new tires are marketed as having great wet traction - another indication that this is the wrong direction.

However, we are talking changing brands and there is going to be some difference btween the way different brands use UTQG ratings as marketing tools. I am under the impression that Michelin under rates its wear values compared to other brands - and that makes 3 hits in the wrong direction.

Overall, this is only somewhat surprising.

Hmm ok. The michelins are each a few pounds lighter (comparing new tires to new tires), so I kind of thought that would offset the weight difference of having full tread again.

I hope the tire difference isn't making the full difference. I went from 33mpg on my tank before new tires, and my last tank was 26-27mpg :(