MPG vs Gearing / tire size

[Rolling18]

Heya,
I'm fairly new to the diesel Wranglers. Been watching TONS of Utube vids but havent seen any that talk about these questions.

Wasn't sure what specific forum to post these questions to as they cover gearing, tire size, and the awesome Diesel!


The wrangler I recently bought has 5.13 gears and 37" in tires. (previous owner many $$$$ mods) he used to run 40's!

As-is I'll get about 19-20 mpg average at 60 MPH @1900K RPM and about 310mi. a tank.
i usually hit 8th gear about 45 mph and rarely drops a gear even going up mild hills at speed.


I would like to eek out a few more MPG.. is this even possible.... other thAn going under speed limit of 55 mph?

Because of the gearing, would I actually get better MPG with 40's tires even though they are heavier?

(re-gearing is not option due to expense)
THANKX!!!

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[ALeeL]

Now I know what not to do with my Jeep. 19-21 mpg at 60 mph? I get 26-27mpg at the speed with stock gearing and 35s. I am not sure why the previous owner went 5.13's, that is overkill for the diesel with an 8 speed— even with 40's. Good luck on your endeavor, but I don't think you will find much improvement outside of regearing or going with a less aggressive and lighter 37 in tire.

 

[Ratbert]

I'm comparison to Wranglers with other engines, you're getting great mileage.

Is your speedo accurate? If not you'll need to get something like a Tazer or JScan to adjust the settings. Having that off can impact mileage and other things.

 

[c20040215]

Wrong forum.

 

[Ratbert]

Wrong forum.

Incredibly "useful" comment without pointing to one that is more appropriate.

 

[c20040215]

Incredibly "useful" comment without pointing to one that is more appropriate.

I really do not have any more useful information.
But if I were trying to get more MPG out it, first thing I would do is to lower it by 5". Remove all the extra seats and interior panels and insulations, remove the spare tire, remove all skid plates. Pump the tire pressure up to 40 psi. All of those are free by the way. Instead of spend money to replace 37s with 40s to save money on gas (if that is even possible).

I am joking by the way. 19-21 mpg is pretty good already.

 

[Ratbert]

If it isn't clear yet: going to 40s is not something that you do to save money.

 

[zouch]

no, probably not.

for reference, i run 37" KM3s (for now) with 4.56s with a couple inches of lift and a RTT and get the same kind of fuel consumption you report at speed.

as has already been said, 5.13s were too low, even for 40s. (4.56 works out just barely on the low side of mathematically perfect for 39s, for reference.)

i'd suggest you start saving your pennies to regear; i wouldn't want mine turning over that fast on the highway all the time. more importantly, i would not want to have to deal with that ridiculously low a gear on the trail when combined with an automatic and the Rubicon 4:1 T'Case.

if you've got the money for 5 new (quality) tires, you've got the money to regear correctly.

Heya,
I'm fairly new to the diesel Wranglers. Been watching TONS of Utube vids but havent seen any that talk about these questions.

Wasn't sure what specific forum to post these questions to as they cover gearing, tire size, and the awesome Diesel!


The wrangler I recently bought has 5.13 gears and 37" in tires. (previous owner many $$$$ mods) he used to run 40's!

As-is I'll get about 19-21 mpg average at 60ish MPH @2100K RPM and about 310mi. a tank.
i usually hit 8th gear about 45 mph and rarely drops a gear even going up mild hills at speed.


I would like to eek out a few more MPG.. is this even possible.... other thAn going under speed limit of 55 mph?

Because of the gearing, would I actually get better MPG with 40's tires even though they are heavier?

(re-gearing is not option due to expense)
THANKX!!!

 

[c20040215]

If it isn't clear yet: going to 40s is not something that you do to save money.

Lets say its not a fairytale, you could really save 2 mpg going from 37s to 40s. Depends on what tire you get, assuming it costs $2500:

Before you spend the $2500, your cost per mile is $3.25 per gallon / 20MPG = $0.1625
Now you improve it by 2 mpg, your new cost per mile is $3.25 / 22 MPG = $0.1477
The difference is $0.0148 per mile.

The break even point is $2500/0.0148 = 168,918 miles, assuming gas price stays constant. That means you start saving money after you have driven 168,918 miles.

 

[grimmjeeper]

Heya,
I'm fairly new to the diesel Wranglers. Been watching TONS of Utube vids but havent seen any that talk about these questions.

Wasn't sure what specific forum to post these questions to as they cover gearing, tire size, and the awesome Diesel!


The wrangler I recently bought has 5.13 gears and 37" in tires. (previous owner many $$$$ mods) he used to run 40's!

As-is I'll get about 19-21 mpg average at 60ish MPH @2100K RPM and about 310mi. a tank.
i usually hit 8th gear about 45 mph and rarely drops a gear even going up mild hills at speed.


I would like to eek out a few more MPG.. is this even possible.... other thAn going under speed limit of 55 mph?

Because of the gearing, would I actually get better MPG with 40's tires even though they are heavier?

(re-gearing is not option due to expense)
THANKX!!!

Weight of the tire has very little to do with overall fuel economy and gearing.

90% of gearing decisions should be based on tire diameter. Weight is part of that remaining 10%.

5.13s are too much gear for the 3.0, even with 40s. The real answer is a regear to 4.10s for 37" tires. Hell, the money to buy a set of 40s would pay for regearing one axle.

You say you don't want to regear and I get it. But that is the best option.

One alternative is to buy some Rubicon axles with 4.10s already in them and swap out your axles. 5.13 axles would be easy to sell.

 

[Wrangler man]

38s are the new 37s. Having started on 35s (which are never a true 35) moved on to 37s. I am 100% happy with my 38s (Nittos) I always air down and that added height makes off-road comfort and clearance just right. With your 5.13 gears you should be slightly better wheel torque and mpg IMO From my research and what I read and also heard on this forum 40s are overkill for the stock Dana 44s and the electronic steering. If you go for these you are committed and then the mods really start to add up. For me and others who actually run 38s and wheel their rig 38s are truly The Sweet Spot. Good luck.

 

[Ratbert]

Lets say its not a fairytale, you could really save 2 mpg going from 37s to 40s. Depends on what tire you get, assuming it costs $2500:

Before you spend the $2500, your cost per mile is $3.25 per gallon / 20MPG = $0.1625
Now you improve it by 2 mpg, your new cost per mile is $3.25 / 22 MPG = $0.1477
The difference is $0.0148 per mile.

The break even point is $2500/0.0148 = 168,918 miles, assuming gas price stays constant. That means you start saving money after you have driven 168,918 miles.

Thanks for doing the math. All that's required is to find a set of $2,500 40s that last 168,918 miles, drive that far, then start raking in the savings!

 

[Rolling18]

Now I know what not to do with my Jeep. Glad I could help!
19-21 mpg at 60 mph? I get 26-27mpg at the speed with stock gearing and 35s. Yes! that would be ideal but I know not close to realistic
I am not sure why the previous owner went 5.13's, that is overkill for the diesel with an 8 speed— even with 40's. In his vids, he claimed was for "snow wheeling" and appearance)...
I don't think you will find much improvement outside of regearing or going with a less aggressive and lighter 37 in tire. I ALREADY am on 37's less agressive gearing may now be in the future after all the responses so far..

 

[Rolling18]

I'm comparison to Wranglers with other engines, you're getting great mileage.

Is your speedo accurate? YES
If not you'll need to get something like a Tazer or JScan to adjust the settings. 1st thing I got was Tazer JL Mini.. adjusted tire size to 35.5 and the gearing! thanks

 

[Rolling18]

Wrong forum.

Thats why I made disclaimer in 1st post.. the engine was most important to me thats why I picket this forum

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