New Shoes, Crappy Mileage

This is very minimal for these two differences in tire sizes, so the calculation is barely affected, not even enough to make 1mpg difference.

 

You need to take your miles drive, multiply by 1.037, then divide by gallons used.

You can recalibrate your UG for the bigger tires. Download the manual and see how to set it up to properly correct for your actual fuel consumption.

 

.592, to be exact.

 

I've been thru the manual and didn't see anything on it. Maybe I have an older version?

 

I still can't believe that going to a 265 would make that big of a change, but I guess there's no other explanation...

 

The Ultra Gauge has a milage calibration. I bought my AT tires by comparing the weight of the tires I wanted campared to the weight of the stock Rugged Fails. I really wanted BFGs but they were just to heavy.

 

You said you have a GPS.... Have you compared odometer readings also? Using GPS and highway mile markers?

Being off a certain percentage will vary depending on how fast/slow you're going.

Where are you from? I get 2mpg decrease/increase when the gas mixture changes between summer & winter gas. My truck gets its best mileage while going about 45mph......Not highway speeds like you'd expect.
Have you changed gas octane lately?

Could be a variety of things 'adding' to your MPG downfall.....

 

I have an old version, there are calibrations for MPG and miles driven. If you have never done the calibrations and are relying solely on that to calculate your MPG's, chances are it was incorrect from the beginning.

 

Seconded.
I went from the stock 245's to a set of 265/75R16 LRC Duratracs, and started feathering the throttle a little more. I take off a little slower and let off the throttle a little sooner to coast down to a stop when I can. I'll still kick her in the ass if I have to pass somebody, and I pace traffic during my commute home (when I go in there's nobody else on the roads).
Before the upgrade I was averaging 22-23; since then I've still managed between 20-21, with one trip to around 18 (spent the weekend hauling a trailer around).

 

Unsprung weight increase will make a big difference. I went from stock sport tires to michelin ltx ms2's (stock load rating) and was surprised at a decrease of about 2-3 mpg due to the increased weight.

 

You said you changed plugs?......what kind did you use????

 

I did find these settings and I did do the calibrations when I first got the UG, so it should have been accurate before the tire change, thanks. I have also checked in the past to see if the UG is accurate compared to the speedo/gal used at time of fill up. I did go into the calibration settings and adjusted the miles driven (multiplied by 3.7%) and it did change the trip MPG to 16.1, not much difference. The MPG calibration is for gallons of fuel and is accurate so I didn't change anything there.

 

Yes, seven thousand miles ago and didn't see any real difference in mileage. Old plugs actually looked great. I used NGK Iridiums. I know you're not supposed to use Iridiums in the 4.0L but I did not have any adverse effects. I've towed a trailer and hauled heavy loads since the plug change and never had a problem with them. I seriously doubt it's the plugs.

 

im enjoying that as well (see Fuelly)

 

I moved from a 265 65 17 to a 265 70 17 and lost about 2mpg around town. You aren't alone on this as like everyone is saying: new tread pattern, larger tire, rotation, etc all play into the mix. If you aren't happy with them, sell them and go back to stock tire and size. There is a reason the dealerships put certain tires on vehicles so the mpg on our trucks look good. Pay the price for your looks

 

I still have my factory sport tires on my dcsb 4x4, which are 265 65 17. I get 21+ all day long on the hwy. I can't see how those tires at 1 size bigger would do that.
I'm planning on going to the dynapro atm in 265 70 17 and wasn't expecting much if any change. Plenty of people have said that tire and size did nothing to there mpg.

 

How? Does the city you drive in have one stop light?

 

The iridiums shouldn't have any adverse effects on the V6, they're just not required like they are for the 4 banger. I don't think that anything you're experiencing has anything to do with the plugs either.

 

Yeah, a few more than 1, maybe just not as heavy a foot as you?

 

Larger diameter tires = less rotations = less odometer reading than actual miles traveled. When I went from 245 to 265. My reading of 10 miles on the odometer was actually 10.38 miles traveled. May not seem like much, but over the a 300 mile tank of gas, that will mean your mpg has dropped by about 0.50-.75mpg in odometer reading. Over time, this will make a difference. This can easily be fixed by having the odometer and speedometer recalibrated. You will also lose some mpg, but not much with a heavier tire. Also, type of tire will also effect this. A street tire is going to be more mpg efficient that a mud tire. It's all on what you are looking for. Do you want better mpg, or a tire that will go offroad and not wear as fast because it's designed to go offroad.