Post re-gear miles per gallon

[Rocky Wrangler]

Last week I had my LJ re-geared from the stock 3:73s to 5:13s. Currently it has Cooper mudders (33s). It's my daily driver and I don't hotdog it too much. I filled it up after the gear swap and ran that tank out yesterday afternoon. When I checked the mileage I almost didn't believe it. Went from average of 12.3 mpg to 16.9 mpg.

What have y'all seen after a swap? I don't usually check all that close as it has the aerodynamics of a tool shed on wheels but that's a pretty big change.

 

[TJ_2000]

Question. Do you on going up in tire size?

 

[Rob5589]

Crazy, eh? And yet there are people that swear by the lowest rpm's possible return the best fuel mileage.

 

[bobthetj03]

Did you correct your speedo? Is it accurate?

 

[Jerry Bransford]

My TJ never reached 12 mpg with its previous 4.88 gearing, it went up to 14.38 after I replaced the 4.88 gears with 5.38's.

 

[Damazzaro]

The biggest improvement to MPGs is when you actually learn when to use neither pedals and coast. Too many people go straight from gas to brake or vice versa.

With that being said. My old Jeep sort of tanked on MPGs when I got 33s and didn't regear.

 

[Rocky Wrangler]

Question. Do you on going up in tire size?

I do plan to increase to 35s in the next couple of weeks.

 

[TJ_2000]

I do plan to increase to 35s in the next couple of weeks.

5.13 with 35”? That’s a steep gear. You can run 37”-40” with 5.13”.

 

[Rocky Wrangler]

Did you correct your speedo? Is it accurate?

Not yet so I'm not real positive on the numbers. For now though I feel good about it haha.

 

[tomtaylz]

5.13 with 35”? That’s a steep gear. You can run 37”-40” with 5.13”.

Depends, if its an auto that's not steep at all due to the OD. My auto 42RLE will be at 5.38 with 35's

 

[Rocky Wrangler]

5.13 with 35”? That’s a steep gear. You can run 37”-40” with 5.13”.

It is indeed deep. I think it may be able to climb trees. Only been a week so far and I am really loving the power.

 

[GTboosted]

What RPM are you at on the highway and what speed?

 

[Jerry Bransford]

5.13 with 35”? That’s a steep gear. You can run 37”-40” with 5.13”.

Not really, it depends on the transmission. My 35's with 42RLE transmission are now running 5.38 gearing and the engine RPMs are barely enough to make things run well at 2600 at 70 mph. As above, my mpg went from <12 mpg to >14 mpg after regearing from 4.88 to 5.38 which indicates the engine is clearly happier not lugging at 70 mph like it was with its previous 4.88 gears.

And no way would I even consider 5.13 for 40's no matter what transmission it had unless the engine was a V8.

 

[Sancho]

Jerry.. what are the issues with gearing ultra low?

Lets say an 05 standard on 31.. going from 3.07 to 5.13? (I am going 4.88 with the intent on going to 32 or 33)

Also, how would a 6 gear differ from a 5 gear transmission? Would I have taller set?

 

[JMT]

Crazy, eh? And yet there are people that swear by the lowest rpm's possible return the best fuel mileage.

This is my experience recorded over the last year and a half of data. I ran for 1 year at 2700-3300 rpm's normal driving. Then I ran 6 months at 2000-2500rpm. So far I am getting better mpg with the lower rpm, significantly better, around 2-2.5 mpg. When I regear I'm going to repeat the test, probably not for that long a period of time, but repeat it for an extended period of time nonetheless. If I get around to it I'll plot all the data on a graph and make a post. I don't care what the results are, I just want to know what they are. There are some stray data points, such as when towing a trailer, wheeling all day, etc...but I can easily see those and leave them out of the conclusions.

I don't know what all issues are involved. I'm certainly not saying that low rpm's is the ONLY factor. I think it could be more complex. I think correct gearing is involved. I think it will net you better gas mileage even driving the same way. And on that note, I am hoping that the gearing is involved, since I'm going lower and would be pleased with higher mpg.

 

[glwood]

Last week I had my LJ re-geared from the stock 3:73s to 5:13s. Currently it has Cooper mudders (33s). It's my daily driver and I don't hotdog it too much. I filled it up after the gear swap and ran that tank out yesterday afternoon. When I checked the mileage I almost didn't believe it. Went from average of 12.3 mpg to 16.9 mpg.

What have y'all seen after a swap? I don't usually check all that close as it has the aerodynamics of a tool shed on wheels but that's a pretty big change.

I think you'll find once you correct the speedometer, you'll see a gain somewhere in the middle. Right now, since the drive shaft is turning faster, the transfer case sensor thinks you're going more miles than you are. Correcting the speedo sensor will fix that. Unless you want to think you're getting better mileage than you are...but it also means you're putting more miles on the odometer than you actually are.

 

[Chris]

I don't keep track, but my MPG after my re-gear is shitty just like it was before.

I suppose I should keep track once or twice, but I guess I just don't care.

 

[Rob5589]

5.13 with 35”? That’s a steep gear. You can run 37”-40” with 5.13”.

5.13 isn't too deep with 33's unless running the 32RE. It would be a little low for a manual trans but totally doable. 37-40" tires on the 4.0 with 5.13 would suck bad. At that point you should be running bigger diffs anyway which can get you into the 6.XX range.

Jerry.. what are the issues with gearing ultra low?

Lets say an 05 standard on 31.. going from 3.07 to 5.13? (I am going 4.88 with the intent on going to 32 or 33)


Also, how would a 6 gear differ from a 5 gear transmission? Would I have taller set?

No issues at all, if you keep your speeds down and off the fwy Gearing the 5 and 6 speeds are the same. The 5 spd has a taller 5th, the 6 spd has a lower 1st.

This is my experience recorded over the last year and a half of data. I ran for 1 year at 2700-3300 rpm's normal driving. Then I ran 6 months at 2000-2500rpm. So far I am getting better mpg with the lower rpm, significantly better, around 2-2.5 mpg. When I regear I'm going to repeat the test, probably not for that long a period of time, but repeat it for an extended period of time nonetheless. If I get around to it I'll plot all the data on a graph and make a post. I don't care what the results are, I just want to know what they are. There are some stray data points, such as when towing a trailer, wheeling all day, etc...but I can easily see those and leave them out of the conclusions.

I don't know what all issues are involved. I'm certainly not saying that low rpm's is the ONLY factor. I think it could be more complex. I think correct gearing is involved. I think it will net you better gas mileage even driving the same way. And on that note, I am hoping that the gearing is involved, since I'm going lower and would be pleased with higher mpg.

3300 is pretty high if trying to obtain decent mpg on the 4.0. What combo was that?

 

[Sancho]

5.13 isn't too deep with 33's unless running the 32RE. It would be a little low for a manual trans but totally doable. 37-40" tires on the 4.0 with 5.13 would suck bad. At that point you should be running bigger diffs anyway which can get you into the 6.XX range.



No issues at all, if you keep your speeds down and off the fwy Gearing the 5 and 6 speeds are the same. The 5 spd has a taller 5th, the 6 spd has a lower 1st.



3300 is pretty high if trying to obtain decent mpg on the 4.0. What combo was that?

So freeway driving means 4.88 are the way to go?

31 - 33s 6 spd.

 

[FireJeep]

Another question..... what is the best RPM for cruising down the highway enroute to your favorite wheeling/camping spot?