Fuel Mileage
 

With the rising gas prices some have called me crazy to be driving my truck. I drive a 1996 Ford F-250 4X4 with a big block 460ci engine. Rather than trade my reliable truck in for a smaller truck or even worse a car:-missingt I have decided to take action and modify my truck instead. My goal is to hit 20 MPG in my truck. So far I have gotten somewhat close. Here is a history of what I have done so far.

1: Had motor replaced after head gasket blew. Mileage before 12 MPG, after 14 MPG.

2: Got mad trying to pull exhaust to fix hole and cut muffler off. 15 MPG

3: Swapped the stock 235/85/16 tires off and put 235/70/16 tires on truck. MPG coming soon.

After my figures for the smaller tires comes in I am going to put a tonneau cover on it. I also have a K&N high flow air filter and at first noticed a 2 MPG increase but then the computer noticed the increase in airflow and now there is no noticeable increase in mileage. I am open to other suggestions and am willing to experiment with parts and other ideas.

:eek:15mpg out of a 460.. there's gonna be a lot of pissed off 302 owners around here.

Yea. I get that at both places I work too. One ranger owner says that he was getting 13 MPG in his '90 ranger. He was very upset when I told him what I was getting with my "gas guzzler." I am hearing that a lot though and it is a bit confusing. Why are there so many small engine vehicles getting bad gas mileage? I am about to make people madder though pretty soon. Initial results with the smaller tires are indicating almost 17 MPG:-jammin

This has been a trial and error experiment. The first set I tried on the rear of my truck were 235/75/15 (yes there are 15" 8 lug rims out there) passenger car tires. Bad idea:-banghead actually killed my gas mileage to just under 14 MPG. I now have a set of 235/70/16 on my truck off of my grandmothers Ford SUV. Except for the fact that they are 4ply tires and the 30 or so miles of county road I drive to work are putting holes in them I am pleased with the initial results.

After I go to drill and back next month I will have the final results. about 400 miles round trip. Also, does anybody have any ideas as to what brand and model tires to buy. The tires off of my grandmothers SUV are not going to last very long and I have yet to find any 10ply tires in this size. I don't think they make them. I could be wrong.

Actually engine size variances, (when engines are running properly), shouldn't effect gas mileage that much when you have the proper tire size and gearing to match the engine size.

Milleage is highly dependant on the weight of the vehicle, and driving habits.

On the freeway, higher tire pressures, low aggression tires, and good front end alignment is a major factor, along with anything that helps reduce wind resistance like keeping your windows up.

Jarod,

What tranny/rear end combo you got in there?
Why smaller tires? just to get a little lower?
And what pressure are you running?

w/ 4.10's and a lumber rack for work there's no way I'm getting past 13.

I think I have the E40D tranny and a 10.5 full floating rear end. Gearing is unknown. I ran with the smaller tires to test mileage. So far it is looking like I am getting almost 2 mpg more with the smaller tires. My route, driving style, and vehicle weight are staying the same. So the only difference is how tall the tire is.

whats the difference in tire height ? you number could be skewed a little bit because your odometer wouldn't be as accurate. you have to take this in to account.

over all that sounds great. I am afraid to figure out the millage on my F250 with the 351 a 4wd I know its gonna use gas. I just try to take it easy.

Have you taken into effect that the speedo if off with different size tires other then stock? So the odomiter woudl be off as well.

To answer both of you, Yes I have taken the odometer variance into account by clocking my routes before the tire changes.

Maybe I'm mistaken, but I could have sworn a shorter tire would make your mileage worse. Being a shorter tire with a smaller circumfrance, it would be covering less distance with each revolution. A taller tire would increase the mileage as it would be covering more distance with each revolution. I know if you get to big, the added weight would require more energy to get going and thus negate any gains in fuel savings.

And yes, I'm a pissed off 302 owner if you're getting 15 MPG in your 460. :D

The taller the tire the more power required to move the truck. If you take a small tire and a big tire and push them down the block you will see that it is easier to push the smaller tire.

The tire size I am using is almost 3 inches smaller than the stock size.

Jarod,

It's been said, and my experience agrees, the route to mileage with a 460 is to make as much torque as you can and then not use it.
With a carburetor on my truck I try to avoid the accelerator pump as well.

I never use 1st and short shift in order to keep the revs down. A 460 has more than enough torque down low with my r/p ratio.

Tire pressure makes a big difference in rolling resistance, and with E rated tires I run them hard (60f-80r) without any wear or traction problems.

Wind resistance increases at the cube of velocity, so keeping your speed down really helps on the highway.
(I can see where lowering your truck by 35mm might make a difference here)

As does trying to keep a steady speed rather than turning inertia (kinetic energy) into heat (braking) and then having to re-accelerate all that mass.

Torque is force, not power, and that is what is required to turn/rotate anything around an axis. (different from your example of "pushing a tire down the road" which is linear effort.)

Good luck in your quest for breaking 20 mpg!

But I'd really like to know what the tag on your pumpkin says....
What are your rpm's @ 60 mph with the 235/85's v/s the /70's?

Agreed...but the distance traveled in one complete revolution will be shorter. Which points to the belief that changing the tire size really doesn't do anything to increase your fuel economy. You're using less power to turn the tire, but your covering a shorter distance. If you use a taller tire, you're using more power but covering a greater distance. The only way to make any real difference is to make minor tweaks...like from a 235/75 to a 235/80. Even then, the difference is so minimal it hardly justifies the change. If you go drastically different in either direction, it actually will make the MPGs worse.

I took the 195/75R14 wheels and tires off my '87 S10 and put 205/75R15 ones on it and picked up a whopping half mile per gallon. The 15" tires stand 1.5 inches taller than the 14" ones. Weight difference is almost nil as the new wheels weigh less than the old one and make up the difference for the heavier tire. The speedo is off by 2-3 MPH. My reason for doing the conversion was for aesthetics, not fuel economy.

In a similar situation, I took the 235/75r15s off the truck in my signature and put 31x10.5 rubber on it. Tires stand 2 inches taller than stock but is significantly heavier with the all-terrain tires. As a result, mileage has gone down just under 1 mpg. Again, the conversion was for aesthetics, not fuel economy.

As shown with my S10, if you can keep the weight the same and not drastically change the height of the tire (basically not altering its inertia), a taller tire will increase your fuel mileage. Otherwise, the fuel saved is counteracted by the decrease in distance covered - and vise versa.

At any rate, good luck with the quest to get 20 MPG out of a 460. I'll be the first in line to say I'll be impressed if you get there. Maybe you've hit on the optimal setup with the smaller tire where the loss of distance is worth the fuel saved.

You can't single out any 1 factor and say with any accuracy that it will increase or decrease milage, you have to look at the difference the change makes to the overall vehicle efficincy. Tire size changes the overall drivetrain gear ratio, changing tire size will have a positive effect on milage only if it allows the vehicle to accelerate and maintain speed with less effort than it did before the change. A truck with 4.10 gearing may see increased milage from larger tires because the motor doesnt have to rev as much, but on the other end of the scale, a truck with 3.08 gears will probably get worse milage because the the motor is under heavy load all the time. It's certainly not a simple relationship, every vehicle will have different requirements.

*raises hand*