Fuel economy with 35 inch tires

[Troop2865]

Bighorn with Off Road package. I added Readylift UCR's and Motofab 2.5 in the front. Tires are 35-12.50-18 Nitto Ridge Grapplers. Fits under a seven foot door by a couple of inches.

As for mileage, it isn't great. Mostly interstate at 70 mph and some two lane road trips to town and back, and I am averaging 14.3. The last tank I checked was within a tenth mpg between the computer and the hand calculation. That tank was 13.9. Even with the stock tires the mileage has never been good. I drive very conservatively, and the best the computer has shown is about 17 driving 55 or so. Interstate with stock tires is in the 15's. I do have the 3:92 gears so that is going to hurt mileage.

I do love the way the truck looks and drives. Hopefully, the mpg will increase as I get a few more miles on the engine.

 

[Troop2865]

I have had my truck a couple of months now and have about 1500 miles on it. I have a few observations regarding running 35 inch tires with the 3:92 gears.

I manually check fuel economy every tank. My speedometer is off .08, so when I fill, I take the mileage for that tank X 1.08 to get the true miles traveled. When I use this figure to calculate actual mileage it is always within a 1/10 MPG from what the computer says.

My last several tanks have been a combination of driving with mostly 2 lane rural highways. I have driven about 500 miles on the interstate since new. My mileage has averaged overall in the upper 13 MPG range, although I did get 14.3 my last tank.

I drive very conservatively. I am not hard on the truck.

We have a large snow storm coming in today, so last night I decided to put my factory 18 inch wheels back on the truck. I have the .ORG so it has the Falken Wildpeak AT tires. I will most likely leave them on for winter.

I drove about 100 miles last night, mostly interstate and some two lane roads. Here is what I noticed:

The truck rides much smoother with the factory tires vs. the Nitto Ridge Grappler tires.

Thus far, the computer shows I am averaging about 2.5 to 3 MPG more. I noticed the bigger difference at interstate speeds.

The engine would rarely kick in to Eco mode with the 35’s. It would only kick in up to about 35-40 MPH tops. Now, the Eco mode is on up to about 60 MPH on flat highway.

As for cost for fuel, others have already said it. The difference is not that much. If I travel 12k miles per year at current fuel prices I am looking at about $225 more per year running the 35’s.

I have owned 20 4x4’s in the past. All but one have been fitted with larger tires. I even had one truck with 42’s ( not very good for Highway travels). Most have been fitted with 35’s. Five have been diesels.

When I was younger I probably didn’t care as much about fuel economy, but I don’t remember losing this much mileage on any of the other vehicles I put larger tires on. I got the 3:92 gears so there would be less effect from the 35’s.

Anyway, that is a lot of rambling.

Bottom line: I still love it with the 35’s. It drives great even with the bigger tires. It has lots of power and the brakes are strong. It is a beautiful truck.

 

[rsonedecker]

On my previous ram, running 2" larger-than-stock tires made my MDS hardly ever come on. When I tuned, and finally calibrated, I saw a noticeable jump in MPG -not huge by any means- but more than just what I expected in terms of correcting for error. I noticed the MDS come on much more often and I always attributed it to correcting the computer for tire size. Wondering if anyone has tested before- and after-tune before- and after-calibration?

 

[Troop2865]

I have wondered about how the recalibration might effect things. I will recalibrate it when I put my 35’s back on this spring.

Like I said earlier, I really like the truck, but mileage is disappointing. I know a few on the forum have said enough is enough on the MPG complaints. I don’t mind people talking about it. It is their truck and they have certain expectations.

I drove a 4wd four door Ford F-150 XLT for a couple days last fall it had the 5.0 which had plenty of power. It was not an FX4 and did not have the lower gears, but I got over 21 MPG on the highway driving 75. I get about 15-15.5 driving 75 with my Ram (with the stock tires- about 13.5 with the 35’s). I do realize anything over 70 with the 3:92 gears really starts hitting MPG hard.

I check every tank so I will notice any change when I recalibrate the speedometer. I will update then.

I would also like to hear if others noticed any increase after recalibration for larger tires.

 

[wthomps79]

On my previous ram, running 2" larger-than-stock tires made my MDS hardly ever come on. When I tuned, and finally calibrated, I saw a noticeable jump in MPG -not huge by any means- but more than just what I expected in terms of correcting for error. I noticed the MDS come on much more often and I always attributed it to correcting the computer for tire size. Wondering if anyone has tested before- and after-tune before- and after-calibration?

Is that hand calculated mpg or going by the in dash computer? I ask because in the past every vehicle I've owned that was tuned (mostly diesels) would show significantly higher MPG on the computer vs what hand calculated was. The new fuel tables always seemed to throw off the computer.

 

[rsonedecker]

Is that hand calculated mpg or going by the in dash computer? I ask because in the past every vehicle I've owned that was tuned (mostly diesels) would show significantly higher MPG on the computer vs what hand calculated was. The new fuel tables always seemed to throw off the computer.

Hand calculate - the computer would have been off because the tires weren't calibrated.

The tune was only shift points for towing, and I had it tuned from the day it was purchased, so the compare was between existing shift point tune and then after I calibrated the tire size (with the same shift point tune). Again, "noticeable", not significant. I was just curious if anyone else had made the compare as it seemed like my truck was "happier" when I calibrated the tires - shift points were better/smoother, MDS came on way more often, etc. I just figure the computer(s) are happier having the right tire circumference, and that seemed to translate into better MPG.

 

[Troop2865]

I always hand calculate. Don’t trust the computer although I have found this one to be very close.

 

[wthomps79]

So by noticeable are we talking 1mpg or 2 or better? I know with my truck going from the stock 275/65R18 to 275/65R20 wheels and adding 2.5" of lift knocked me down almost 3-4mpg which I was a bit surprised it was that much. I was able to average 15-16mpg now I'm down to 12-13 on a good day. Its interesting that just re-calibrating the computer could make much of a difference.

I've been hand tracking my mpg off and on since I got the truck and I also have to admit that its usually within 1-2 tenths each time.

 

[rsonedecker]

I'd post actual numbers, but I don't remember exactly to be honest. It was more of I went from "You've got to be kidding me that it's dropped this much" to "Okay, that makes much more sense". If I had to give a range, I'd say it was ~2 MPG. Again, the truck's manners and engine performance (especially highway) was different. I had bumped up tire sizes before on previous trucks, but this was the first time I went a whole +2", and it seemed like when I told the truck "Hey, you've got much bigger tires on", it seemed much happier. YMMV.

I won't be able to wait to put my 34.3" tall rubber on right when I get the new truck (and I'll immediately re-calibrate) - otherwise I'd experiment myself.

 

[TimmyG]

Very similar experience with 35x12.5’s and 3.92 gears. Power loss was barely noticeable. I’m getting about 10 city / 18 highway.

Here’s a screenshot from a 2hr all-freeway trip today:

View attachment 8365

Curious what type of highway driving you do? Flat or hills, mph ranges, etc. Thanks!

 

[blownout1500]

Curious what type of highway driving you do? Flat or hills, mph ranges, etc. Thanks!

hilly, lead foot

 

[Creep0321]

Noob question, but how do you calibrate for tire size? And does this also fix the speedometer?

 

[Troop2865]

Rough Country has a device that allows electronic calibration for different ride sizes. When you enter your tire size, don’t just believe the tire manufacturer’s stated size. Measure the tire diameter to make sure.

 

[Tommy R]

I appreciate everyone's input here, especially the well thought out, detailed comments. I just picked up a new Rebel and I've been rather surprised the mileage is as bad as it is. It would be naive of me to expect to see the EPA figures on the sticker, but to see 12mpg in a mix of city/hwy is pretty disappointing. I don't romp on the throttle much, either. The truck is bone stock and has 1000 miles on it now. Maybe it'll improve over time? We'll see! I suspect a major culprit are the Goodyear Duratrac tires that come standard on the Rebel. They're super gummy and the tread blocks squirm like crazy, though the ride is not bad for an E-rated tire. I believe they may have a very high rolling resistance so when it comes time to replace I'll be going with something different....and milder....like a Terra Grappler. It should roll smoother, but still be adequate for the offroading I'll subject the truck to.

The unfortunate thing is the plans for the truck will just make the mileage worse! LOL I will take it overlanding and so it will be leveled with 34s or 35s, and I just installed my rooftop tent. I absolutely know these things will negatively impact my economy so I'm trying to do my best to do whatever I can do to minimize the pain at the pump.

Has anyone experimented with higher octane? So far in my very limited testing I've run 87 and 89 octane (in Texas), but haven't yet seen any significant difference so I'm inclined to stick with the cheap stuff! I will eventually put a tuner on it and a CAI, but would like to retain the ability to run cheap gas, if possible. Of course I'll also recalibrate it whenever I decide to put taller tires on.

I will say this... Though I'm currently a bit disappointed in the economy of my truck, I would absolutely buy it again. It makes up for the economy in so many other ways! It was my first new vehicle purchase in 23 years and so far, no regrets at all!

 

[User_7869]

I got 34’s 3.21 and I average 15. I had 35’s on it for about 2 weeks and i could feel the drain on the power. I didn’t like it at all. When they put the 34’s on it felt almost like it did stock.

Interesting comment. I noticed a little more "floaty" feel in the steering on uneven roads and a little drain on power overall, but I dig the look of the larger setup. I have the 3.21 gear ratio. I need to make sure the odometer is accurate for the larger tires too.

 

[SilverSurfer15]

I just picked up a new Rebel and I've been rather surprised the mileage is as bad as it is. It would be naive of me to expect to see the EPA figures on the sticker, but to see 12mpg in a mix of city/hwy is pretty disappointing.

so me too here, but I think whats happening is this:

1) I think these tires weigh 55ish lbs each if I'm remembering correctly, thats pretty heavy. The other trucks with P rated tires are like 38 I think?

2) The tread. its pretty aggressive. And while weight is probably the number one factor, a highway tire has alot less rolling resistance vs an aggressive all terrain like these.

So these two things hurt the mileage, but I think if you switched to a 34-35 that you wouldnt really notice as much as a hit as you normally do on other trucks that switch from lighter P rated tires that they only put on there for mpg reasons.

12 does seem pretty low, im in the 14ish range mixed. But I dont much "city" driving per say. Can barely average 16 on the hwy though at all lol. more like 15.

I'm coming from a ecoboost truck that averaged 19ish, so I'm super thrilled about it. I used to daily drive a 6.0 2500HD gas truck on 37s that would average about 12 not ever going over 65, so having a stock half ton get anywhere near that is a bit of a pisser.

 

[TimmyG]

hilly, lead foot

What tires and lift are you running and what area of the country are you in? Thx

 

[TimmyG]

But the look is worth the fuel loss

Those look niiiice! How's the tire howling at 70 mph? I recently road in a new F150 with 35x12.5R22 Toyo Open Country MTs. They weren't extremely loud, but definitely noticeable. You could talk over them without having to yell, lol

 

[Truckin]

My 16' Ram Crew 4x4 has 3.21 gears...I tried 285/65R20 BFG KO2's using Bilstein 5100's set to 1.4" height to level and while they did fit, performance took a huge hit-dropped to 275/65R20's and regained performance. Did not keep 285's on long enough to check actual mileage but based on performance hit and dash MPG it would be about 2mpg. The 285's were only about .5 inch taller, a tad wider but weighed almost 6 pounds per tire more...

 

[Troop2865]

I just filled up for the first time since putting my factory wheels and tires back on for winter. Most of the miles were interstate but I also had other mixed driving with this tank.

The computer mileage showed 16.5. When I hand calculated the tank it was actually 18.1 MPG. I was pretty stoked with that number.

I only have about 1600 miles on the truck now since I have an economy car to drive the majority of the time. I think the latest number is good considering it is an ORG truck with 3:92 gears.

As much as I like the increased mileage the truck just isn’t right without the 35’s.