New jeep. Mpg / gearing questions

[Kinz384]

The gearing proponents don't seem to understand that a regear doesn't do anything outside of 1st gear that a downshift doesn't already do...automatically. If gearing lower increased fuel economy you could just drive around in 4Lo and get 20mpg. The engine doesn't see axle gearing. It sees load and final drive ratio and that's it. It doesn't know the difference between 5.13s in 8th, 4.10s in 7th or 3.45s in 6th as they all have the same final drive ratio of 3.45-1. Bigger tires increase load. Heavier tires increase load. More wind resistance from fenders, racks, snorkels, etc increase load. More weight increases load. Lift kits and their increased drag adds load. Gearing doesn't change any of that. Sure it helps a little at take off in 1st gear but everywhere else is doing nothing but causing the transmission to upshift sooner. Watch just how little time you spend in 1st gear in the road with 5.13s. Why would a few minutes a day do much for mileage?

That does make lil more sense.
So what can I do to help.
Go to 4.88.
get a lighter 37.
or go 40’s lower rpm

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[JTdiRtyD]

Beginning to think regearing is a myth. lol.
I know few extras on Rubi but damn.
Am I wrong for thinking.
Stock jeep. 19 mpg
Sport. 37. 16. Mpg.
Would assume if regear. Back to 19. Or closer.
But. Get Rubi. 37. Regear. Few extra parts. &. Goes to. 12-13!?
That’s seems a lot. I could see 16. I would think it would be close to the struggling sport.
Seems like I’m losing 5 mpg.

But ….. maybe I’m just ignorant to how much of diff it makes.

With 5.13's you're sitting 500 rpms higher at, as an example, 70mph vs with 3.73's. 500rpms can make a big difference in mpgs. Upsizing to 40's is only going to lower that by about 100rpms. As an example, my diesel will see about 2mpg lower in 7th gear vs 8th gear, which is about 400rpm difference.

In addition to the increased rpms, you are creating more wind resistance with a roof rack.

That does make lil more sense.
So what can I do to help.
Go to 4.88.
get a lighter 37.
or go 40’s lower rpm

It seems like you're just wanting us to tell you what to do. No one here can say for sure what will fix the problem, and it's up to you to take the information given to you and decide what you're willing to do and see what results you get. We aren't going to do it for you.

 

[Kinz384]

You’re right I am asking. I’m asking people more knowledgeable than I am. On what they think will be best option.
And I appreciate all input.
So far. I’m assuming. Lighter 37’s
Will make more difference than the 40’s.

 

[JTdiRtyD]

You’re right I am asking. I’m asking people more knowledgeable than I am. On what they think will be best option.
And I appreciate all input.
So far. I’m assuming. Lighter 37’s
Will make more difference than the 40’s.

My suggestion, as I've stated before, is to remove the racks and see what happens. It's free and simple to do before dropping money on new tires. Will it give you 5mpg? Probably not, but it might help some to where lighter 37's can make up the rest of the difference. Then it's up to you if you want to reinstall the rack and take the hit or not.

But I very much doubt lighter 37s alone are going to give you what you want, especially only 10lbs per corner.

 

[Kinz384]

My suggestion, as I've stated before, is to remove the racks and see what happens. It's free and simple to do before dropping money on new tires. Will it give you 5mpg? Probably not, but it might help some to where lighter 37's can make up the rest of the difference. Then it's up to you if you want to reinstall the rack and take the hit or not.

But I very much doubt lighter 37s alone are going to give you what you want, especially only 10lbs per corner.

I get. It won’t net me 5. Just curious if lighter or 40’s. Which would do more.
these current tires have prob 50% tread or less. So new tires are coming either way.
kinda want the roof rack. So can put pvc & black pipe on top when needed.
sport just has bed rack & the pipes would scratch up the hard top.

 

[Kinz384]

Hey, congrats on the new Rubicon sounds like a beast for your plumbing gigs! Yeah, those 5.13s are definitely cranking the RPMs higher than the 3.73s, which can tank MPG a bit, especially with the bigger tires and racks.

Thanks. 5th jeep. 1st Rubicon. I like it. !

 

[Zachanadandy]

If the OP uses it for plumbing work he needs the racks for 10' or even 20' pipes. The wind resistance and even the higher rpm are negligible as most of his driving is in town. All he can do for that use is run the lightest wheel and tire package he can and even there it just won't be great. Short of removing a bunch of weight (again hard to do with a work truck) it just won't be a huge improvement in my experience. My 1 ton service van was lucky to get 11mpg but it was HEAVY. Now that I'm a general foreman the company prius gets 60mpg...and I can drive in the car pool lane solo. I guess that's why we run heavy 37" MTs on the JT and heavy 39" MTs on the wife's JLUR and just don't worry about the fuel economy? Regearing to try to save fuel economy is pointless. Even changing wheels and/or tires would take a long time to pay for itself. As an in town work truck I'd guess at most 20k miles per year. 16 mpg would be 1250 gallons per year. 13 mpg 1538 gallons. 288 gallons per year at $3/gal is an annual savings of $864. New 37s would be likely double that cost. Regearing locally is $3k, even if it saved you 3 mpg (which it won't on my experience) that's 3.5 years just to break even. Expensive mods to save fuel in a lifted Jeep is like buying expensive lingerie for hookers, it will never make sense.

 

[Gvsukids]

Maybe it's the snorkel.

 

[Kinz384]

Yes sir. I avg. 26k. Miles. Yr. On the sport.
I rarely carry pipe. Usually have supply shop deliver. But when I need to. The bed rack has been extremely useful.
Some of the other stuff on Rubi. Is not needed work wise. But. Being honest it looks cool as shit. So. I’ll eat that.

40’s. Would look awesome also. But sounds like lighter 37’s. Is the smarter choice.

 

[MPMB]

1. Aerodynamics - The Rubicon with the stubby/mid bumper, winch, stinger, flat fenders adds more resistance. The Sport also has the filler panels between the bumper and fenders that improve mpgs.

2. Tire rolling resistance - Between weight and traction/contact patch, that will affect mpgs.

3. Weight - The Sport is 400# lighter than the Rubicon in stock configuration. Rule of thumb is every extra 100lbs, mpg decreases 1%-2%. 400 pounds would be 4%-8% decrease. 14.7-15.4mpg for the Rubicon compared to the Sport, at stock configuration.

 

[Kinz384]

From past. I had.
tj - Sahara - 35’s.
wife’s jk wrangler 4 door - golden eagle -37
Xj - 4.88. - 35’s.
jt - sport. -37.
Hell. The grand wagoneer. With 33’s & roof rack. With 6.4. Hemi.
all get better gas mileage than the Rubi.

I think I just had misconception on gearing. And expected diff
& my weight is the biggest factor.
I guess good news. Is nothing is wrong with jeep. So that’s good. As never know when buy used.

 

[Gladiatorx2]

I have 37's and a 3.5 lift on my Rubicon, as well as a fairly heavy front bumper and winch. After lift and on 34's I averaged about 17.5 mpg. After the 37's I have averaged 16.8 for the last 4500 miles. I am running 4.10 gears with the auto.

My mpg is very similar to yours on the Sport with 3.73's. I am in East Tennessee and have as much uphill as downhill. Even though my fuel economy is the lowest of my previous three Gladiator I am happy with it. I have had nothing else on 37's that could accomplish it!

Driving style, use and load probably have more to do with it, but yes a lighter wheel/tire combo would help.

 

[Kinz384]

Maybe it's the snorkel.

Would that effect flow. ? Cause diff? That. I don’t have much prob getting rid of.

 

[Kinz384]

I have 37's and a 3.5 lift on my Rubicon, as well as a fairly heavy front bumper and winch. After lift and on 34's I averaged about 17.5 mpg. After the 37's I have averaged 16.8 for the last 4500 miles. I am running 4.10 gears with the auto.

My mpg is very similar to yours on the Sport with 3.73's. I am in East Tennessee and have as much uphill as downhill. Even though my fuel economy is the lowest of my previous three Gladiator I am happy with it. I have had nothing else on 37's that could accomplish it!

Driving style, use and load probably have more to do with it, but yes a lighter wheel/tire combo would help.

So do the 5.13 hurt more than help me on the mpg

 

[tom.mary.glad]

From past. I had.
tj - Sahara - 35’s.
wife’s jk wrangler 4 door - golden eagle -37
Xj - 4.88. - 35’s.
jt - sport. -37.
Hell. The grand wagoneer. With 33’s & roof rack. With 6.4. Hemi.
all get better gas mileage than the Rubi.

I think I just had misconception on gearing. And expected diff
& my weight is the biggest factor.
I guess good news. Is nothing is wrong with jeep. So that’s good. As never know when buy used.

I regeared when I went to 37s not for mpgs but hopefully to reduce wear and tear on the transmission and engine. Some will disagree that regearing helps this and that's OK. I think it reduces stress on tranny.

I have Sport with Max Tow so I went with 4.88s which very closely matches the 4.10s and stock 31ish tires.

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