37s giving 2.5 MPG better than stock?

[Chans4x4]

The previous owner averaged a little over 12...seems like it was 12.49 or something like that. The difference is only in the driving style, terrain and traffic. If you can't understand how the difference in RPM's vs road speed (which is changed by tire size)....well, I won't even go there. Bigger man than you. I will avoid being condescending and will continue to share information with anecdotal evidence not just rhetoric. Have a great day!

Wanted the thread to ask if others have experienced the increase in gas mileage on the highway. 100% thought I would loose MPG. With a 37 mud tire load range D or E and probably aftermarket rims with a combined weight of over 20lbs more per tire than mine it is probably not possible for most with 37s. Makes me feel I’m not crazy since Gladiatorx2 experienced the same thing.

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[Gladiatorx2]

Mine were Fallen Wild Peak AT3. They were Load Range D. I ran them at 33 psi cold. My lift was AEV 2". I did have an ARE topper. I drove it approximately 100 miles a day on mainly state highways. Counting stop lights and rolling terrain even though I usually ran 60 miles average speed was generally 42 to 50 mph. Anything 70 or over it dropped to 17 mpg or so. I do think that the performance and driveability would be greatly enhanced by a gear change. It just wasn't worth the expense to me. Programming the new tire size is critical too. I hope this helps.

 

[Sigz]

How in the heck are you getting 22.7mpg with 37s!??

I have Falken at3ws (33s) and I'm avg 17.5mpg right now. (Stock Sport S) I'm no speed demon either. Seemsl like 17-18.5 is my best.

 

[BlueScapegoat]

If you're somehow actually getting better mpg with bigger tires it's an extreme outlier with some odd combo of factors at play, because that isn't the case pretty much ever, and for many reasons. Understand that at a base level in pure physics, it takes more energy to push that vehicle down the road than before. You've increased rolling resistance, you've increased drag, you've lengthened gear ratios which can be viewed as a series of levers doing work, you've increased rotational mass, you've increased unsprung weight. The only place you may logically gain back some mpg to offset some of those negatives would be where the engine falls in the rev range on the highway, and that depends on the brake specific fuel consumption of the engine at that speed. The engine is still being required to do more work at speed, and at a lower rpm that means it needs to produce more torque to do it. If you're comparing a heavy 33" MT to say a relatively light 37" AT it's possible you've knocked the rolling resistance down some while keeping the weight somewhat in check. Not quite an apples to apples comparison of better mpg with bigger tires though. I've always recommended the KO2s for folks that mostly drive street because they roll nice, they're quiet, and they're light. Also worth noting the KO2s run infamously small, so a 37 we're talking about is really much closer to a 35.

What psi are you running the tires at? Just running the larger tires at the correct psi usually increases rolling resistance massively. If you balloon them up to just run on the center tread section you can get better mpg at the expense of your tires and it won't last for long.

::edit::
keep in mind as well that wind plays a huge role in that mpg math, people never seen to take that into consideration. Just a 10 mph wind from the back turns that 70 mph drive into a 60 mph drive, and it's not linear. Aerodynamic drag increases at the square of speed. You need either a huge data set to get a good average from or a repeatable back to back test to get anything solid.

 

[Gladiatorx2]

I know that it goes against the grain of what would be expected. I also know that not everyone will see the same results with some not even getting close. In reading the post you will see the same Gladiator but with the previous owner averaged nearly 10 mpg less. I have exceeded the mpg posted by the EPA on every vehicle that I even owned with the exception of a BMW X5 with the M Performance Package and I struggled just to reach it. On the final trip to trade it in I averaged 63 mph. My average RPM was around 1750. I had as many downhill grades as uphills. I did not use AC ( April). I drove with the instant mpg display on and tried my best to obtain the best fuel economy. That is what I got. On the way back with the Max Tow on my first tank my average speed was closer to 72 mph. My average rpm was around 2100. I only got 21 mpg. The true difference in tire size was about 5 inches in diameter/height. The wheel/tire weight was around 112lbs vs maybe 70 on the Max Tow. I averaged 23.2 up to around 5k and at that point went to 315's. I dropped down to a true 20.3 before correcting for the tire change with Jscan. After correcting on the first couple of tanks I have an average of 21.9 mpg in combined driving. I will drive several thousand miles after the lift and report back. I only post from my personal experience and not what I read or had seen somewhere. I simply reported my experience to tell others what is possible and not what they will experience. I had a Charger Hellcat and averaged over 21 mpg. I had a Ram 2500 with the 6.4 and averaged about the same. It's all in how you drive.

 

[guntrust]

I can confirm similar improvement in highway fuel economy (close to 20mpg) after i upgraded to 37's and regeared to 5.13 (city is also slightly improved). I have heavy accessories. Also, stick.

 

[YYCSahara]

My mpg also improved by 1mpg going from a stock Mojave to AEV 2" and 37s.

I went from 15 to 16 mpg. Yes they are KO2s which are very light and I chose 17" wheels which are also very light. I reprogrammed the comp to say I have 35.75" tires. I had the Falken MTs and they were horribly loud and probably had more rolling resistance compared to AT KO2s. I"m just happy the MPG didn't plummet.

 

[Bbannongmu]

Sub’d. This will help me sell the idea of 40s to my wife - probably be Prius level mileage

 

[Hemy5587]

Well I thought I was just crazy but my daily drive is just about 50/50 city/highway. Everyday, every week for over a year I averaged around 16 mpg hand calculated (sometimes dipping into the 15s during the winter). Same drive, same speeds. Switched from 35" goodyears to 37" bfgs in July, E range to C range so somewhat lighter but bigger diameter and have been creeping up on my average. Started at 16.5 mpg then to 17 mpg a tank and now my last fill up was a legit 18.06 mpg. Same drive, same speeds with my speedometer corrected and about 2000 miles on my new tires now. Sport S w 3.73s but 3.23-ish w 37s so that would help on the highway part I guess.

 

[Gladiatorx2]

Did you adjust the speedometer to the new tire size?

Yes

 

[Northshoremb]

I havnt tried highway driving yet but going from 33" wildpeaks to new rims and 37" Kanati Trail hogs got me going from #90.6 to #98.6 for the 37"​

What i want to know is everyone just using JSCAN to input 37" and running it or actually doing it the right way and choosing tore size that actually matches the GPS speed while driving down the road to get the exact correct speed, mpg numbers? I kept adjusting 1/4" at a time until the speed and distances were dead on​

 

[Gladiatorx2]

I used Jscan on the Max Tow. On the 315/70r17 Goodyear's it ended up being 34.4 which was verified with radar. On the Rubicon it was done at the dealer. It was also dead on by radar. The two that I purchased new on the stock tires speedometer showed 2 MPH fast as confirmed by radar. So in the case of the last Max Tow prior to correcting for the 315's indicted 55 mph was actually 59 on radar. But remember when new at same speed 55 mph indicated was actually 53. So the true speed difference prior to correcting was 6 mph or over 6 %. At least from being truly accurate. Also after correcting the driveability and acceleration returned to near stock. Sorry for the long post but just wanted to detail my experience.

 

[DailyMoparGuy]

I havnt tried highway driving yet but going from 33" wildpeaks to new rims and 37" Kanati Trail hogs got me going from #90.6 to #98.6 for the 37"​

What i want to know is everyone just using JSCAN to input 37" and running it or actually doing it the right way and choosing tore size that actually matches the GPS speed while driving down the road to get the exact correct speed, mpg numbers? I kept adjusting 1/4" at a time until the speed and distances were dead on​

I always just round down to the nearest value listed by the manufacturer.

For example, Mickey Thompson list my 37/12.5/17s at 36.7in so I put 36.5in into JScan. My speedometer is accurate with my gps app at 75mph.

 

[Hemy5587]

I havnt tried highway driving yet but going from 33" wildpeaks to new rims and 37" Kanati Trail hogs got me going from #90.6 to #98.6 for the 37"​

What i want to know is everyone just using JSCAN to input 37" and running it or actually doing it the right way and choosing tore size that actually matches the GPS speed while driving down the road to get the exact correct speed, mpg numbers? I kept adjusting 1/4" at a time until the speed and distances were dead on​

This is exactly how I got my speedometer calibrated, I kept adjusting until it was dead on. I started with measuring the actual tire but felt like it wasn't quite correct so I kept adjusting until it was there.

 

[Northshoremb]

This is exactly how I got my speedometer calibrated, I kept adjusting until it was dead on. I started with measuring the actual tire but felt like it wasn't quite correct so I kept adjusting until it was there.

Yep so many people just measure the ture and input without actually checking accuracy. I did that on our 2 door but after using gps and looking at both speed and distance I found every Kilometer I was off .2 so that adds up fast for oil change or selling mileage as well as throws off Fuel consumption calculations. I say start with the measurement with a level as starting point then keep adjusting till speed is literally dead on and the distance is too then everything will be accurate. My current tires are 36.25" mounted but needed to go up to 37.25" in JSCAN to have it dead nuts on

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