Significant fuel mileage drop after upgrading to bigger wheels.

[sedgett23]

Hello. So I added 20x9 wheels with 35x12.50x20 tires to my 2019 F250. My mileage went from 17-20 to now its best average is 14.3. I know there is an expected drop of a 1 or 2 mpg however I am down 3-4. My truck is completely stock as far as the engine and drivetrain. I do not race it around and I don't drive in alot of stop and go traffic. I have gone in and set the revs per mile and disabled the Use VID option, and set the gear ration to the correct ratio and I am still getting awful mileage. Are there other things I am missing with adding bigger wheels and tires? My buddy has the same setup on a 22 f350 and he is consistently averaging 20 mpg. Frustrated at this point. Any guidance would be greatly appreciated.
Oh also I do have the wheels correctly inflated....

[Toad0407]

The 22 has 4 more gears which helps it a lot, hence the higher fuel mileage. That drop of 3-4 is to be expected with bigger wheels and tires. 14.3MPG isn't bad at all, and that's what I see mixed driving 50% highway 50% city.

Something that may help with your mileage is some good tuning, and perhaps a weight loss(if you know what I mean How often does the truck regen(exhuast cleaning)? Frequent regens will kill your mileage.

Another way you can bump it up is by replacing the 35x12.50x20 tires with something that has a narrower profile, like a 295/65/20, running a less aggressive tire, etc.

If I were in your shoes, I would: Get some good tunes, verify fuel filters are clean, get a good CAI(I run a S&B and have seen some gains), idle as little as possible, and see where that takes you. I would not expect to be back at that 17-20 but you will see gains over your current 14.3.

[jetskier]

I have a hard time believing 20mpg with 35's on any truck. I see the same 14-15mpg mileage with mixed driving in my 2013 with 295/65r20s. I might see 17-18 highway if I keep my speeds below 70mph. You have to remember the rotational inertia is the mass times the radius squared. You increased both factors with the larger tires and wheels over stock. It just takes more energy to turn them.

[sedgett23]

I spaced he had the 10 speed s part of my calculations for mileage. I had the fuel filters replaced when I bought the truck 2 months ago so those are good. Tracking heavier wheels and tires, rotational mass and all that, I knew there was going to be a drop in mileage I just wasn't expecting it to be that drastic with the setup. I am guessing a tune and CAI intake at minimum will help some. Not sure on how often it regens, this is my first diesel so I am not sure how to tell how often thats happening. I guess the main point to my question was really to find out if I what happened to my mileage is what should be expected with the change in setup and it sounds like its an expected result. Thanks for the rational replies to dumb questions, seems like most places you try to find info for things you just end up getting hammered by douchebags about how dumb you are... Thanks again.

[Toad0407]

My reply was no way, intended to hammer you. My reply was to just simply explain the possibilities as to why you are seeing a bigger drop than anticipated and some tips as to how you can get back to the MPG you were having. If you need recommendations as to what tunes, etc. Feel free to contact me and I can help point you in the right direction. But I'm just a douchebag, so take the advice how you want.

[jetskier]

Another thing to consider regarding transmissions is the shift points. The factory transmission calibrations are setup for optimal mileage before driveability. You probably notice it lugs more before commanding a downshift. With a tune, this is usually refined for more driveability, but it comes at a cost of a fuel usage since you are usually going into higher RPMs on both up and downshifts than stock thereby using more fuel. This is where the 10-speed probably shines over the 6-speed.

[sedgett23]

So I have an extended warranty for my truck that I can't violate for a couple of years so doing a delete and whatnot is not in the cards right now. However I am open to getting two tunes for now, one for true daily driving and traffic and then one for when I haul my 16 foot enclosed trailer for racing. Not sure how much tuning can be done for a stock setup but I would be interested to hear your guidance on where to get a good set of tunes for these particular driving situations....

My reply was no way, intended to hammer you. My reply was to just simply explain the possibilities as to why you are seeing a bigger drop than anticipated and some tips as to how you can get back to the MPG you were having. If you need recommendations as to what tunes, etc. Feel free to contact me and I can help point you in the right direction. But I'm just a douchebag, so take the advice how you want.

[Toad0407]

I will send a PM.