I am wondering what kind of mileage some of you other guys are getting with 37inch tires. I have been dividing number of miles since last fill by number of gallons to fill up for the last 4 tanks and came up with 11mpg each time. I know this is probably about 10% low due to the speedometer being off by about 10%, but this still seems low to me. Please post if you have 37inch tires.

04 PSD CC LB AT 3.73's
11mpg average

 

tell you what i am running 35's and by hand my combined mileage (hwy and city) is anywhere from 12.8 mpg to 13.6 mpg, so your not far off and your calc on the percentage off is right on also. with the 35's my stuff is off 6 to 7 %. I think with 37 inch tread you have to go to 4.56 gears and i need 4.10. by my calcs that brings it back to very close to stock. check out Currie Enterprise website look closely for a link to calculators and there you can play with tire sizes and gear ratio's let me know what you do?????? And how is your off the line stomping onit acceleration. My just sort of stinks it's like i'm winding a rubber band once it starts rolling then it takes off. This is my firsst diesel so I'mm stil learning how these things operate. Iknow Banks or The edge performance computers would fix all this sh#t but what about warranty.

 

Have you calibrated your systems for the bigger tires? A 37" tire will really skew your mileage if uncorrected. The dealership diesel tech said that Ford is clamping down on recalibrations on tires because of EPA concerns. I don't know why. That is what he told me.

 

No, I haven't calibrated, that's why I figure my mileage is probably off 10%. But my warranty is going to be 10% longer too. So far, I don't believe there is a way to calibrate for 37's.

But, back to the original thread. Anyone else out there have a crew cab with 37's and an automatic? I'm trying to get mileage comparisons with a similar truck.
Thanks
Steve

 

I got the superlift truespeed on mine. i checked it with a gps and i was off about 7 miles per hour at 60 and only about 5 at 35 mph. it comes out to about 2 miles off for every 20 miles driven. so you actually drove 22 miles when it says 20. that was very close for my setup anyways. i used to get about 330 before fill up before i got the true-speed so i would divide 330 by 20 miles and multiply that by 2 and thats how much i would add for the bigger tires. so at 330 it was actually 363 driven. oh and i have 37's
hope this helps, jamie

 

Do you have the 6.0? I thought it didn't work on 6.0s.

 

YES i have a 2004 6.0 it uses the same true-speed as all the superduties gas or diesel. works great pretty easy to install to.
jamie

 

I have 37's on mine, and I need to get the milage thing fixed too.... pics of my truck here http://community.webshots.com/photo/...35478450eMlJPc

 

Realistically until you correct the speed-o there is no use even trying to figure it.
Too far off!

 

Why would you not go to a speedo shop and have it re-calibrated? I was about 10% off when I put my 315's on, the speedo shop took 10 minutes and about 50 bucks to fix it. The speed factors into a lot of tasks that the computer performs. I thought I was going to have to run to Randy's to get 4.10's, but the recal brought the shift points within tolerance (for me at least)

 

I have an 03 6.0 with a superlift 8" lift and 38"s, I went with 4.56 gears and I am getting about 12 mpg, combined avg, other than the lift and tires, the rest of the truck is stock, (for now), hope this helps for comparison, also you may want to check the pressure in your tires, mine were set at 25 psi, and was getting 11-11.5 mpg I took them up to 50 psi and now it's running 11.5-12,

 

dealer told me they could only flash to a 265/75/16 tire, as that is the largest ford equipped a sd with..............and they wanted 90 bux to do it....told em forget it. i clear dtc's all the time, and the flash procedure is not a whole lot different, the tool is just more expensive
no way id pay more than 50 bux!

 

It used to be $50 bucks at the dealer I used. Like the tech said, they don't want to do it anymore.

 

Hey all. New diesel owner checkin in. And yes, I've read the guidelines

Quick question for socaldavis: What type and size of lift did you put on your truck. I was thinking about putting 37's with 17" rims on mine. Thanks!

Great group here. Lots of helpful information.

 

Well if you have read the Guidelines...........then WELCOME