With so much discussion of MPG loss with larger than stock tires. Is this due to the additional mass that needs to be rotated vs the stock lighter setup?

I have a 96 Impala SS with larger than stock tires/wheels combo but I went with a lighter rim/tire combo and corrected tire diameter with programming (LT1_edit/TunerCat) and it did not hurt the mileage.

So in theory, if you put on a larger tire/wheel combo with the same weight as the oem setup and with correct PCM programming, MPG should no be affected?

Just curious.....

Rotating mass, and tread design, imo, going to a 265 all season tire will be minimal if not improved, but most are jumping a couple sizes, and going to a more agressive tread. Lugs are going to kill milage on the highway compared to a rib, ask any trucker.

I went to 265 BFG ATs and lost 1.5mpgs. All on flat ground, 50/50 hwy / city miles.:(

Same here, retired the original 245's w/ 265 AT's, and lost ~2mpg. But w/ a GPS a couple years ago, I discovered my speedo was never correct for the stock 245's. So my original mileage (~19mpg) on the stock tires was BS to start w/. It was overreading by ~4% from the factory, which I proved w/ a GPS over a 440mile trip (GPS) where the odo showed 460miles. With 265's, it's right on.

Tim

Make sure you guys correct the mileage for the speedo error you get with the larger tires.

I started with 265s, and my mileage with 285s was about the same. 295s dropped it a little bit, and my current 315s seem to be maybe a tad worse then the 295s, but I just got the 315s and need to get some more tanks to know for sure.