Hey guys. I know there has been a ton of posts in the past on this topic, but I just wanted to let y'all know that I figured out my gas milage after putting on my bigger tires and redoing the gears. I went with 35's and 4.56 gears, kept the M5OD stock, no engine mods, only 3" exhaust and I am getting 16.4 mpg on the highway. I don't drive like a skinned cat, but do the limit and only got passed twice on a 2 hr drive. I am really happy with this, espically with the big tires. Just thought I would share that info with you incase there is anyone wondering about milage with bigger tires and lower gears.

 

bchunter- Consider yourself one of the fortunate few. The only way installing larger tires increases MPG is by changing your final gearing so that your cruise RPM is closer to your engines peak torque. Your situation is unique. Larger tires, which are typically also wider, almost always require more power to turn. An exception would be going form a C rated tire @35 psi to an E rated tire @ 80 psi. The higher pressure tire offers less rolling resistance and consumes less power.

 

When I was looking at which gears to go with, I used some of the calculators on the web and the 4.56 have me doing 2100 to 2200 rpm when I am going 100 kph which is the limit around here. I do consider myself lucky. I thought my milage was going to go way down, but it is basicly the same as before when I had 30's and 3.55 gears. I just wish I was that lucky this weekend while hunting

 

The 83 Ford spec manual says peak torque is achieved at 1600 rpm.

 

Interesting. I thought it would have been a little higher then that. At what RPM does it carry the torque to before it starts to drop, or is the drop quick right after 1600?

 

for a carb'd 300, id say the useable power band is peak of 1600 to about 3000. i charted a carb'd 300 on DD2K and the power band fell off about 2500 and at 3000 is was kaput. not i know DD2K isnt the best for real time data but still a good place to start.

i get between 13-15 mpg with my 93 F150 on 33s with the E4OD and 3:55s. but thats a mix of town/highway. the 5 speed trucks always seem to squeek better milage out, perhaps its because of the extra gear and little better OD ratio.

 

I'm running 35"s with 3.54 gears and an np205 and got 15mpg runnin around 85 mph for about 2 hours straight on the freeway. I also have a fortune in my engine, it would probably do better if it didn't have a Holley carb.

 

I can't get this motorcraft to run right, but haven't had much time to tinker with it (about 30 minutes) but I hope that it will be better than the holley when it comes to fuel. I am only getting about 13 mpg. I actually think bigger tires would help because it would lower my rpms.

 

Except big tires put more rubber on the road = more friction and resistance.
Also big tires weigh alot more.

 

It's more like a flat line.

 

Right on. Thanks for filling in the mental gap.

 

True. The only way bigger tires would help is if they were just taller, not wider. But then again, they would weigh more.

 

I have found that my milage in my other trucks would increase if I went up "one" size, such as 31 to 33, but I am amazed at my truck going from 30's to 35's. Glad I regeared it.

 

I can't imagine my truck running 33s without being regeared, going from 3.08s to 4.10 whew! What a difference that made, mileage is terrible but the power mmmm ! Just right!