ok i upgraded to 20s on 33s i figured that i would lose a mpg or so. my speedo is now off bout 5 miles a hr. how can i figure out my mpg? im lost on this. with the speedo still off 5mphs i am getting 14.7 miles per gallon. where as before i was getting 15.6 mpg.

does the 5mph change make a diffeance in my mpg?