bad mileage?

[JLDickmon]

def the tires. while they are the same height as a 285, they are wider...thats heavy...get some ligher tires on there and that should drastically help.

same height as a 265
or a 235/85

but a ****load wider

 

[ghoff]

Big Joe - Fuel filter gets changed every 15k, and air filter is (or was) clean during time of tests. 3.73 gears.

Living in California, I'm not too sure if we get winter blend here. The tires are BFG All Terrain's and I'm not sure that they are known for fuel mileage to begin with. Unfortunately they are only load range D. I can't seem to find a good all terrain tire in an E range.

Unlike most Californians, I do use the truck OFF the road too. So I do like having wider tires. But do you guys really think that would make for such a big loss in mileage? Also would finding an E range tire help?

JL-I'm not familiar with your tuner. Can you point me in the right direction? 5 MPG is friggin HUGE! That's what I'm talking about.

Thanks

 

[BIG JOE]

Well then..

Look into JL's tuner, Shim yer Fuel pressure up to 70 psi, do the tank and fuel pump inlet mods.. to get the air out of the fuel and the HX mod to equalize yer injector (oil) pressure

All of those equal more efficiency.. might get some MPG from that too

Maybe a turbo Wicked Wheel too

 

[JLDickmon]

Well then..

Look into JL's tuner, Shim yer Fuel pressure up to 70 psi, do the tank and fuel pump inlet mods..

I talked to Jody for about half an hour.
Told him what I hauled, how often, what it weighs, what kind of trailer I use, what kind of tires are on the trailer, what the terrain is like around here, what tires I was running on the truck, what the gear ratio of the truck is, how many miles a day I drive, how many of those are on the highway,

never occurred to me to shim the FPR, it would help with atomization of the fuel, not necessarily fuel economy per se...

If I ever have the occasion to drop the tank, I'm gonna Hutch it. (I have to pull the bed here soon and fix some body damage, maybe I'll do it then)

 

[BJS]

are you compensating for the larger tire in your economy calculations or have you recalibrated your speedometer?

FWIW I haven't been able to find a load range E tire in a 305/75/16 as that is what I would love to have on my truck to help give me some legs with the 4.10 gears.

as for tire size the 305/75/16 is taller and wider than a 285/75/16

Metric sized tires are as follows

Section width in MM / height width ratio / rim size

so a 305 tire is 12" wide
and 285 tire is 11.22" wide
and 235 tire is 9.25" wide

so 75% of 305 is 228.75 or 9" X 2 + 16 = a 34" tall tire = circumference of 106.8" ~ 7% larger than a 235/85 tire
and 75% of 285 is 213.75 or 8.4" X 2 + 16 = 32.8" tall tire = circumference of 103.0" ~ 3% larger than a 235/85 tire
and 85% of 235 is 199.75 or 7.86" X 2 + 16 = 31.72" tall tire = circumference of 99.7"

I think the 235/85/16 is the stock tire size for the truck in question
so right now your odometer is showing 300 miles traveled when consuming 23.077 gallons of diesel

you actually traveled 321 miles using the same 23.077 gallons resulting in an economy of 13.9 or basically 14 mpg which is not too abnormal for winter fuel in a stock truck for around town driving. If you're running highway then it should edge up a bit higher if you keep the rpm & speed lower.

 

[GOEGLEINBROS]

My money is on the tires..

 

[clintusaf]

I think the 235/85/16 is the stock tire size for the truck in question
so right now your odometer is showing 300 miles traveled when consuming 23.077 gallons of diesel

you actually traveled 321 miles using the same 23.077 gallons resulting in an economy of 13.9 or basically 14 mpg which is not too abnormal for winter fuel in a stock truck for around town driving. If you're running highway then it should edge up a bit higher if you keep the rpm & speed lower.

I measured this a while back on a trip and you are correct with the calculations. I was wondering about it myself and i go a few miles further with my 285/75/16's than what my odometer reads, which means a tad bit better fuel mileage than what appears.

 

[whiteduty]

First of all, I dont think the tires make that big of a difference in your fuel economy. 2nd the size 305/75R16 doesn't exist, it may be a 305/70R16 which is the same height as a 285/75R16 tire. If you check the tire specs a load range D 305/70R16 tire will carry as much or more weight than a load range E 235/85R16 tire. It is the volume of air that supports the weight, not necessarily the load range of the tire. The 285/75R16 are available in load range E tires. I only get 10.5 mpg in the winter (around town diving) and it jumps to around 12.5 in the summer,I am running 315/75R16 tires, if I am on the freeway I can get up to 16-18 mpg, and I have gotten as much as 20, but that was running about 55mph, which doesn't happen much. But on the other hand we dont drive these trucks for the fuel economy. If that was our main concern we would be driving a geo metro, or worse yet a Dodge.

 

[ghoff]

Whiteduty - My bad...You are right I am running 305/70's, not 75's.

BJS - Not sure what size tires came stock on the truck, but I bought the truck used several years ago with 315/75R16 mud terrain's. The speedo was reading slow at the time. When they wore out I put the 305's on in hopes of better mileage. There was practically no change. The speedo seems to be just about dead on according to the roadside radar signs.

Thanks for the advice Big Joe.

 

[JLDickmon]

Whiteduty - My bad...You are right I am running 305/70's, not 75's.

BJS - Not sure what size tires came stock on the truck, but I bought the truck used several years ago with 315/75R16 mud terrain's.

Thanks for the advice Big Joe.

OE is/was LT265/75R16 E
anytime you guys need engineering data on a tire, I have a table..