bonez

Unless you have had your PCM reprogrammed, you're milage and mpg's on the dash are incorrect.

digdeep0169

well thats interesting to know. No - i haven't had my PCM reprogrammed... but it seems like I'm getting Terrific gas mileage! I've owned my truck for 2 months now and have been to the gas station twice. (then again my commute to work/play is close) next time I'll calcuate # of miles driven vs re-fuel and get an exact count...

bonez

You won't be able to just calculate that from the odometer on your truck either, as it too is not correct. The dashboard display is calculated from stock tire size and since you have changed to larger tires, it will throw the computers calculations off. Your speedometer will also not be reading correct, as you will be traveling faster than the speedo is showing.

Here's an example from my stock tire size to my new 35's...

Stock size: 275/65R18
Stock diameter: 32.07"
Circumference: 100.7"
Revs/mile: 648.5
Speedo: 60mph

New size: 35x12.50R20
New diamter: 35.02"
New Circumference:110.0
New Revs/mile: 593.9
Actual Speed: 65.5mph

Speedo Difference: 9.193% too fast with 35's

To get an accurate set of numbers, use this formula:

# of miles traveled on tank of gas (from dash) * 1.09193 = Actual # of miles traveled

Divide Actual # of miles traveled by the number of gallons of gas on fill up

This will give you your true mpg's.

If you were to get a tuner (like the Edge Evo, which is what I have) you can reprogram your PCM to calculate for the change in tire size. Also keep in mind that even from the factory, the MPG's that are displayed on the dash are typically inflated slightly from what you are actually getting if you were to calculate # of miles traveled / # gallons to fill up.

Hope this helps.

Southern_FX4

The open country 35 and my rockstar rims would weigh 120 with the 33 it would weigh 112

Southern_FX4

I also have the edge cs programmer to reprogram for the difference

HoppyFX4

Ever thought about meeting in the middle? I have 34.1 BFG AT (275/65/20) and I avg 14-15 city with 17-18 hwy with an Edge EVO and K&N drop filter.

HoppyFX4

Pic of tires

nickalopalus

I was going to suggest the same thing. I also run 275/65/20. I feel like its a nice happy medium, it's a good size tire and doesn't completely ruin gas mileage.

redefinition1

I am running 35" M/Ts on my 20" rims, and would not want to go smaller. For me, the rim to tire ratio seems just right. Also gets that little bit more ground clearance and I believe better performance off road, if those are your intentions. I get around 12-14 city and 15-17 hwy mpg, with an 06 4x4 with the 4.6 and stock 3.55 ls rear end. Those numbers go up or down depending on how I'm feeling that day/how much of a rush I'm in.

Most recent picture:

Southern_FX4

Well I bit the bullet today I ordered the 36x12.5x20 toyo open country. They should be in tomorrow. I'll post pic once they are on. Went with the 35 because if I ordered the 33 I know I would reget it that's a lot of money to regret.