Well I finally got rid of the 20s today, kinda sad but oh well. I traded mine for some stock aluminium 16s and some cash. The truck pulls it self around a lot better and get these MPG gains.

I had to drive 190 miles, each way, to the guy I was trading. So I figured I would see what the MPG differences were between the two sets. So I filled up before I left, then after the swap I filled up again. then when I got home I filled up again. So 3 fill ups today. The trip was all highway. The guy I traded was able to recalibrate the computer for the new size tires so both tests were with the correct computer settings. These are the results:

31.25' 20's @ ~95lbs EACH!! 16MPG

28.75; 16s @ ~ 56lbs 21.5MPG.

The MPG gains are great since I am hopefully getting a new job which is farther away. The trip down there I drove ~72 MPH and the trip back I drove ~75 MPH. The performance is alot better. Even thou it is a stock 4.8 which is slow, I am just not as slow now. And it actually stops now, before braking at speed was such a PIA.

I was getting 12 City and 16 highway. This is all with the stock 3.42 ratio.

 

Oh I forgot to mention. One way down there the truck TC unlocked several times and it kicked out of OD about 7 times. On the way back the TC never unlocked and it never kicked out of OD.

 

what gears do you have?

 

see first post 3.42

 

Yea it was funny when I said that I got worse mileage from my 20's and nobody believed me. Everybody said it was only because my computer wasnt reprogrammed. I sad that 1-2" diameter larger doesnt make a 4mpg worse difference. Some people just dont use their brain too much. They are heavier and harder to turn, down the quarter or the highway.

 

Yup, that's why I still have my stock 16's. They're not the most attractive wheels in the world but at least they are lightweight and beneficial for performance. What size tires do you have and who makes them?

 

You sure those are the correct diameters values that should have been programmed?

What tire size did you have before and what size do you have now?

 

I had 275/55/20 before and 255/70/16 now.

I had the 20's checked 3 times at the dealership and once with some kinda GPS thing. 16's reprogrammed with a tech II. However the first fill I had took like ~11 gallons and the second one took ~8 gallons.

 

Yah I have went from my 20's to my stockers, althought it doesn't look as good, the truck sits lower, runs a **** load better, as you my gas mpg has went up, thats why I am looking for some smaller rims

 

those are great gaines man from just a tire and rim change.
my 20's are pretty light with the same height tire but a little wider and i've really never notice any loss in mpg.
oh and the 255/70's are 30" tall.