I just replaced the bald stock tires on my 04 Grand Cherokee with 245/70r17 General Grabber AT2s and went from about 20mpg on highway to about 15.5mpg. Is this common or am I in need of a serious tuneup?
The new tires are a bit wider then the stock ones, which will give some more resistance with the ground, but the mpg difference is too big. Did it really change directly after changing the tires?