So we just bought a differant truck, stock tires are 245-16, we are running 265-16 Speedo is 5 mph off at hwy speed. With 245 the truck ran 70 mph at 2050 rpm Recalabrated the speedo with the sons handheld tuner and the truck does 70 mpg at 1900 rpm. So we are getting 18 mpg without the recalabration, couldnt leave the recal. in long enough to see the real mileage. How doo I figure mileage with the 265 tires???? Dino
I dbout it changes very much at all ...
a 245 to a 265 is less than a 1" change in overall tire diameter ...
Even though the engine RPM is lower, a lot of times you get WORSE miledge because of that .... there is a certain RPM most gasoline motors are designed to operate at peak effeciency at, and typically that is ~2,200 rpm ....
I know that when I went from 245's to 285's on my current truck, my engine rpm's went down by about 3-400 at 70 mph and I'm actually getting worse miledge, unfortunatley
I don't know, there are also differences in tire weight from the factory tires. Factory tires are typically pretty weak and light weight in order for them to claim higher miledge ... I know that also on my old truck, going from the factory 265's that I got between 17 and 19 with on the highway, going to an LT-rated tire I went down to 15 and 17 with no other changes....
i guess the moral of the story is there is more to it than meets the eye than just tire diameter.
