If you installed Triple Treds, You definitely lost mileage. They're a heavy tire & cause mileage drop. I know that from my running a Goodyear store & personal experience. Easy to check the weight of the tire is to go to tirerack.com. Look up your previous tire & the new tires and check the spec page on both. Willing to bet money I don't have that they're heavier than your OE tires. Unsprung weight is always overlooked - wheels/tires,etc. Of course, check the basics - tire pressure, similr driving conditions ?, etc.

When I got the General Altimax HP's for the Sentra, I compared them. The triple Treds are 4lbs heavier per tire in the same size.

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Sharing my partner's 2012 Forte 5dr SX til I find my next 123 or 126..
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Do I miss being a service advisor ???