Need some advice. My 2011 xlt ecoboost 3.55 gear 2x4 was getting about 18.5 highway (70 mph). Leveling the front end 2.5" had no effect that I could tell on the mpg economy.
The problem came when I put on the pro comp. 285s. I took it to the dealership and the computer was updated for the bigger tires so it should be accurate. But I'm averaging 16.5 at the same speeds/same commute now.
Overall the mpg is not where I want it to be.
I have not towed with the truck and shouldn't have to anytime soon. No travel trailer or anything like that.
I love the look and set-up of the truck right now. So what are my options for getting close to 20mpg?
My only thought, without changing the tires, is to change the gears.
Would 3.15 be an OK option for my highway commuter needs?
Or 3.31....
Thanks for the feedback all.

 

Tires make big difference on mpg. When I went from the stock all season tires on my 99 to all terains of the same size I lost 2mpg also. All due to higher rolling resistance, every time i took my foot off the gas it was like putting the brakes. With tires you either get mpg or traction, the more traction the less mpg and that is with staying with same size. If you up size now you change weight and overall gear ratio too.

 

Thanks! Yea I went from the stock 265s to 285 all terrains so they're a bit bigger.
My main question at this point is about the gearing. I realize if I go 3.15 it's going to down shift when going up a hill, and with bigger tires that changed the gear ratio.

If anyone has a link to a good thread post about gearing please paste it here.

 

It will take tens of thousands of miles driven at 2 mpg's less to pay for a gear swap. I'd leave it be and don't sweat it.

I was going to increase my size from my stock 235's to 265's like on my Expy but I may have to rethink that idea.

 

We just have to remember that every thing is a compromise. Ford chose the stock tire to deliver the lowest cost, best mpg and then traction, wear and looks.

I agree, a gear change will never pay for itself and the Ecoboost has plenty of power for any of the gear ratios. I also don't think a regear will improve the MPG by more than a trace amount due to the increase in rolling resistance and weight gain of the bigger tire.

 

Thanks that's helpful. Which truck of yours has 235's?

 

Larger, heavier tires with a deeper, more aggressive tread use more gas. IMO, it is not worth 2 mpg for a better looking tire. If you are using the size and tread for regular off roading, the sacrifice is more likely worth the price in gas.

But 2 mpg will really cost hundreds of dollars worth of gas over their lifetime, so do consider that.

George

 

My 2011 has 235 75R 17 and my Expy has 265 70R 17. The tires on my F150 are bologna skins but looking back at the 80-96 trucks with 15" wheels makes me realize that these really aren't so bad.

 

I think 3.15s are too far the other way.....

 

Since you increased the diameter of the tire, you effectively decreased the numerical value of the gear. If you dropped down to a 3.15, you would most likely loose more mpg. The height is not realy the big problem at work here, it is the rotational weight of the tires. The vehicle requires a certain amount of Torque to move, or maintain speed. By adding rotational weight, you are now requiring more torque to maintain the given speed. Combine this with the loss in mechanical advantage (effective reduction in gear ratio), the increase in rolling resistance and you have the mpg losses that you are experiencing.

In your situation, you would need to change to a lower gear (higher numerical number) in order to reduce the load on the engine. This load is part of the fuel consuption difference.

 

I tend to agree under certain applications. But, let us remember the old 80-86 F-150's that were using the 300 I-6 and 3.08 gear sets. These trucks weren't fast nor economical but they did get the job done.

 

Well if anybody is interested in my old 265 70 R17's let me know. In Tx

 

So after about 1,000 miles with the new tires I've noticed that the shudder I used to feel as I came to a stop is almost completly. This coincides with the installation of the new tires.

 

I went through the same issue when i put Bilstein leveling shocks and 35" tires on my truck. Went from 17-18 mpg down to 15-16 but the truck looks so much better with the bigger tires!

 

I don't know about the economical remark that powertrain often produced 18-20mpg... but of course that was usually in reg cab 2wd truck that only weighed about 4200lbs.. not a 6000lb super crew 4x4.