Getting new tires on my 01 Blazer 4Dr LS. Stock tires are 235x70x16, but im looking to upgrade. The guy ay townfair told me the biggest he would reccomend I go is 245x70x16 which is a 29.5 in diameter with the Eldorado Sport Plus. Im wondering hoe badly this will affect my mpg, I get about 20 mpg on mine. Also would the spedometer be thrown off? The guy said it wouldnt with these tires but im looking for some more firsthand advice.