I recently had 4 new Goodyear Assurance Fuel Max tires installed on my 2010 Subaru Forester. They replaced the OEM Yokohama Geolanders, which did fine and gave me about 54,000 miles of service.
I’ve driven a little over 1,000 miles since purchasing the new tires. The Goodyear store had them inflated at about 29 psi, I increased it to 34 psi - same as I inflated the previous OEM tires.
I specifically chose the Fuel Max tires to improve fuel efficiency. They received high marks from Consumer Reports for their low rolling resistance.
So why oh why has my mileage gone down by 15% across the board? That decrease is about the same for both city and highway driving.
What method are you using to compute your mileage? What is your highway/city result? Are you in a cold climate? Is your car’s other maintenance up to date?
I ask because the difference in rolling resistance between the worst and the best tire on the market might cause a 1% to 3% change in mileage. 15% indicates some other problem or an error in computing mileage.
I’m relying on the Subaru’s built-in trip computer to calculate mileage - same method I’ve used before & after buying the new tires. It’s always proven pretty accurate when I’ve checked by the old-fashioned manual measures.
Weather has been relatively temperate for this time of year in Northern Indiana (30’s & 40’s). Vehicle is regularly maintained.
Haven’t changed anything else since buying the tires, but I saw an immediate drop on the first tank of gas after getting them. (I reset the MPG calculator at each fill-up.)
There is a technology triangle between Treadwear, Traction (especially wet traction) and Rolling Resistance. In order to get an improvement in one area, one (or both) of the other items has to be sacrificed.
You took off a set of tires with a UTQG rating of 320 B A - and put on a set with 560 A A. That means better treadwear, and better traction - so there has to be a loss of fuel economy.
It is likely that the OEM tires had GREAT RR - and they got that by sacrificng the traction (B rating!). The FuelMax tires have good RR for tires with high treadwear ratings, but compared to tires with low RR (and poor traction), their RR is not as good.
Plus, new tires will always have worse fuel economy than worn tires- all other things being equal. So as the tires wear, they will get better fuel economy, but it is unlikely that they will ever get to the same level as your OEM’s. On the other hand, they will last longer and have better traction.
I wasn’t all that pleased with mine either. Put them on mY pRIUS AND MILEAGE WENT OWN FROM 52 TO 47. However, the weather is also colder, so that accounts for some of the difference.
Worn tires turn more than new tires over a given distance.
So your old worn out tires were telling you that you were going slightly further than the new tires are telling you, which skews the calculation.
Plus, you didn’t mention if you bought the exact same size tires.
You also didn’t mention what size the actual tires are.
If it is the Base X version of the Forester, then the tire size is 215/65-16.
Yokohoma shows their tires spin 768 times for every mile traveled.
Goodyear shows that their tire spins 774 times per mile.
That’s a pretty big difference between two tires, and will add up over a tank of gas.