Bigger Tires, Better MPG on 3.0?

[Tredsdert]

I know, typically the thought is that bigger tires means more strain on the engine and more contact on the road, also bigger tires are heavier, so typically it's thought that bigger tires mean lower MPG. I would be out to say this is true on most gasoline engines, namely because they are a little less beefy and powerful typically than a similar sized diesel engine.

What I'm wondering is, are the diesel engines with all of their beefiness negating those things that would otherwise be strains on the engine, lowering miles per gallon, and just moving right past them unaffected. Without all of the outside factors, weight, resistance, strain on the engine and other parts, and in a perfect environment, bigger tires would mean better miles per gallon.

All of the people I see talking about their 3.0 EcoDiesels, the ones who are saying they're getting near 30mpg, all seem to have 37-in tires. I know from watching @Casey250 that the Eco-Diesels have no issues running 37s without re-gearing. I believe all he had to do was put in a taser JL and update the tire size on the dash, so that the speedometer matched.

I currently am getting an average of 23 mpg on 32-in tires. I'm curious to know what everyone else with the EcoDiesel is getting for their average miles per gallon, and also what their current tire size is?

I'm wondering if there might be correlation here, bigger tires on the EcoDiesel might mean better miles per gallon, versus other vehicles where bigger tires means less miles per gallon.

If you would, EcoDiesel owners, please list your average MPG and current tire size. Thanks and looking forward to everyone's answers.

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[Deleted member 59498]

I get 22 to 24 something like that on whatever Rubicon is, 33s? 32.5? Maybe if I put 40s I will get 31mpg?

 

[SilverSurfer]

I am yet to meet a Jeep owner that is completely honest about their MPG. You can take those MPG figures of the diesel owners with the big tires with a pinch of salt.

Unfortunately one cannot argue against science, roll resistance is a case in point - Bigger tires on a Jeep means worse MPG.

 

[blackJLURubi]

I get 18-22mpg with 37s

 

[Grayhound]

I’m on stock ko2 and I’m seeing 21 mpg average right now. Granted I have quite a bit of idle time here in the winter. In the summer I was seeing 27 hwy at 72mph and 22 city averaging 24.

 

[jlandry287]

I’m getting 23 - 24 with stock 33” KO2 tires. No lift, just factory rubicon.

I live in south louisiana so it’s flat flat here

 

[Ratbert]

Sorry, our diesels don't have magic science-denying MPG fairy dust sprinkled on them.

Unless, of course, you're making the tires bigger by simply inflating the crap out of them.

 

[grimmjeeper]

One could make the argument that 3.73s is more gear than is appropriate for stock size tires. At least for freeway driving. I would bet a dollar that the diesel would have come with 3.45 gears if the front M210 had them available.

Even with 35s I'm pushing 1,800 RPM at 75. With 33s you're up closer to 2,000.

Ideal cruise RPM for the diesel is probably 1,500-1,600.

So going up in tire size would partially balance out with better highway RPMs. In theory at least.

So maybe the hit to MPG isn't quite as bad as it is for a gas engine. But that's just a guess on my part. I have no data to back it up.

 

[Ratbert]

One could make the argument that 3.73s is more gear than is appropriate for stock size tires. At least for freeway driving. I would bet a dollar that the diesel would have come with 3.45 gears if the front M210 had them available.

Even with 35s I'm pushing 1,800 RPM at 75. With 33s you're up closer to 2,000.

Ideal cruise RPM for the diesel is probably 1,500-1,600.

So going up in tire size would partially balance out with better highway RPMs. In theory at least.

So maybe the hit to MPG isn't quite as bad as it is for a gas engine. But that's just a guess on my part. I have no data to back it up.

Couldn't that be verified by downshifting?

 

[Zandcwhite]

The biggest factor in modern Jeeps is wind resistance/drag. Bigger tires mean higher profile and usually wider. Gone are the days that Jeep owners cruised around at 50mph max as that's all a lifted tj could muster with big tires and the top off. Most of us drive freeway+ speeds and get poor fuel mileage. The faster you go and the taller your rig the worse it gets period. Whenever someone posts an absurdly high fuel economy and backs it up with the trip computer, their average speed is below 50mph. One guy even had an average speed of 35mph over a 1500 mile trip. I'll drive fast and buy gas if that's what it takes to get great fuel economy from a Jeep.

 

[White Rhino_21]

I’m typically cruising around town on my 2” lift w/35s and will achieve 19.5-21.5mpg on average.

I’ve taken a few trips from Atlanta to Nashville and I’ve averaged 22.5-24mpg on each occasion. During these trips I tried to maintain the speed limit to keep my RPMs low and it never did much from an MPG standpoint, but certainly annoyed those professional drivers hauling freight. Running 5-10 mph over the speed limit is when my average would be closer to 23mpg on the highway.

 

[Tpsillos]

on my stock 255/70/18(32.1") I would average 29(mostly highway around 65mph). After adding 38's it went down to 22mpg. Changed to some gas rubi axles(4.10 gear ratio) it went back up to 24mpg. I did some engine work then it went back up to 26mpg on 38's!
I moved a few months ago and rarely get over 35 mph... my mpg took a pretty big hit down to 22mpg. The roads traveled and your right foot is the biggest factor!

On side note my 07 megcab 6.7 will get 23 mpg on 38's with some heavy engine mods. Factory was 17mpg even with factory size tires.
These newer designed diesel engines do better on fuel milage than the older ones but there is still room for improvement.

 

[TX_Ovrlnd]

Sorry, our diesels don't have magic science-denying MPG fairy dust sprinkled on them.

Unless, of course, you're making the tires bigger by simply inflating the crap out of them.

I inflate mine with helium so they are lighter, take that physics!

 

[jrice454]

I’m typically cruising around town on my 2” lift w/35s and will achieve 19.5-21.5mpg on average.

I’ve taken a few trips from Atlanta to Nashville and I’ve averaged 22.5-24mpg on each occasion. During these trips I tried to maintain the speed limit to keep my RPMs low and it never did much from an MPG standpoint, but certainly annoyed those professional drivers hauling freight. Running 5-10 mph over the speed limit is when my average would be closer to 23mpg on the highway.

Same as White Rhino, 2023 with 1500 miles on it and I'm lucky to get about 22 mpg with 60% highway and 40% city. I have the Mopar 2" lift, stock K02 tires, and a Maximus-3 rack up top. Lift and rack obviously add some drag but I would have expected better mileage.

 

[rickinAZ]

The more unsprung weight, the worse the performance/mileage. Taken to the extreme, bicycle tires would be the best "performer".

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