MPGS
Lead Driver
Joined: Oct 2003
Posts: 8,476
Likes: 37
From: Madison, WI
Yeah, it's astonishing how much bad alignment will spoil MPGs.
Also, to the OP, if you're running 35s and the PSOM is still calibrated to the OEM 235/85s, the speedo and odo are both reading low, so you're actually getting about 1.5 MPG than you're calculating.
Also, to the OP, if you're running 35s and the PSOM is still calibrated to the OEM 235/85s, the speedo and odo are both reading low, so you're actually getting about 1.5 MPG than you're calculating.
Hotshot
Joined: Feb 2009
Posts: 10,410
Likes: 77
From: Plankinton, SD
Bigger tires = less rpm Glenn, I'm not sure you want that, knowing how your truck is used. I've went from 305/70 tires that were on it when I got it, and 3.55s, to stock height tires and 4.10's.
My mileage isn't as bad as yours either. Yours just likes fuel
My mileage isn't as bad as yours either. Yours just likes fuel
Cargo Master
Joined: Nov 2010
Posts: 3,244
Likes: 40
I assume you have 235s? I prefer a 265 or 285. The thing is with your truck you go tall and skinny not tall and fat like a mud tire. If you have since a super single semi tire, that is the idea.
I know you tow alot but 13 unloaded is bad news. HellI get 15 and my truck weighs about 1500 pounds over a stock crew.
I know you tow alot but 13 unloaded is bad news. HellI get 15 and my truck weighs about 1500 pounds over a stock crew.
Cargo Master
Joined: Jul 2010
Posts: 3,014
Likes: 115
The numbers that you are referencing are all widths, though, not diameters. You effectively just told him that he needs to get a wider tire.
Hotshot
Joined: Dec 2005
Posts: 14,377
Likes: 609
From: evansville in
Especially them brakes.mine had a bad caliper on rf and stuck parking brake cable therfore parking brake on at left rear.its a wonder it did as well as it did.mileage came up several mpg just from that.
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Cargo Master
Joined: Nov 2010
Posts: 3,244
Likes: 40
Glenn,
I know that you tow a lot so I wouldn't go too big. Hell I have 315/75/r16 tires with 3.55s and it still isn't the best. I'm working on a deal to swap for 4 10s. Although if I am going 65 I am running about 1500 rpms so you can't even hear the motor running. She really prefers roads with a 75-80 mph limit though as she just keeps on trucking.
With a 5speed, 35 inch tires, and man trans my truck would be about 2000 at 65 which is just perfect, since I don't like to drive fast.
An auto with overdrive would be about 1800 rpm at 65.
A 32 inch tire would put you at about 2000 at 65. A 235/75/r16 is about a 29 inch tire, 265 is 31 inch, 285 is a 33. I'd run a 265 or 285 tire and call it good. It doesn't hurt your pulling power all that much and I would be willing to bet money your cruising mpgs go up which would bring your entire average up.
IMHO diesels don't like rpm, they prefer to run real low. We have different torque curves than most semis, but I know the two big trucks that we run like to be shifted at 1200-1300 rpm.
Fleet Owner
Joined: Aug 2004
Posts: 20,419
Likes: 197
From: AZ
oops, I stand corrected. I did last year put on 265/75's Toyo's on the rear. A well trusted shop owner talked me into them, said they were bullet proof under a load like I carry. So far, they have been good tires. It didn't change my mileage from before to now. These injectors I have been a mystery sense I got them. They are suppose to be baby beans (130 cc's) but I know they can't be with the amount of smoke I can pour out. I've had them now for seven years and this winter they are coming out and going to JR. I've blamed my poor mileage on them but I'll see what Jim Rose says.
Cargo Master
Joined: Nov 2010
Posts: 3,244
Likes: 40
oops, I stand corrected. I did last year put on 265/75's Toyo's on the rear. A well trusted shop owner talked me into them, said they were bullet proof under a load like I carry. So far, they have been good tires. It didn't change my mileage from before to now. These injectors I have been a mystery sense I got them. They are suppose to be baby beans (130 cc's) but I know they can't be with the amount of smoke I can pour out. I've had them now for seven years and this winter they are coming out and going to JR. I've blamed my poor mileage on them but I'll see what Jim Rose says.
Posting Guru
Joined: Mar 2009
Posts: 1,799
Likes: 0
My gfs truck will be lucky to clear 15 with her stock 7.3 and a TS chip. Now assuming the stock TS tunes are on the chip then you can remain getting that mileage until you get some real tunes on that thing. There's almost no difference with TS tunes and stock PCM calibration LOL
Cargo Master
Joined: Nov 2010
Posts: 2,797
Likes: 10
17.5 hand calced every tank if any town driving is involved, long straight trips 18.5 - 19 mpg at 65-70 mph... Towing 8k+ 11-12. I have a chip but untill I get a few things cleared up I have ran this on the stock tune since I bought the truck and played with the chip mpgs...