5.13 or 4.88??? Please Help.

[Rubicon_Fan]

Good day,

It's now time for my jeep to get new gears. It's way to sluggish on the hwy with the trailer Behind.

Before I ask let me give you some info of my jeep and a trailer.
It's an 07 JKU Rubicon (manual) with factory 4.10 gears and 4:1 transfer case.

In the last 3 years I've modified it and added extra weight:
35" Goodyear Wrangler w/
17" alum wheels (9" wide)
Front mid width bumper
Winch
Rear full width bumper w/ tire carrier (full spare)

Plus a trailer
It's an M101 CDN, with 130lb lid, and matching wheels and 35" tires, RTT, Awning, nose box. (about 1300 lbs dry) My jeep is a second vehicle and I use it mostly for my camping/fishing/hunting/expo trips.
Now, when I'm on a hwy, I found my jeep is extremely sluggish at hwy speeds. My 6th gear is pretty much useless And im getting really crappy mileage On a flat hwy, no hills, well under 65 mph (95-100 km/h) , I'm getting 13.5-14 mpg (16.5-17 L/100 km) towing my trailer (not fully loaded) and 2 people in the jeep,

So I need your opinions in this: Will re-gearing help me on a hwy speeds? and will they help to improve my MPG? I've done my fair part of reading on Jk forum an such, and it looks like folks there go for really high gears only to be able to rock crawl and don't really care about Mileage. But for me, I love exploring and do it as much as I can, but with gas at $5+ a gallon ($1.40 per litre) I really care about mpg.

So what gears do you think should I go with? Is 5.13 too high and waste of gas on a hwy? Or is 4.88 just enough for my needs?
I'm stuck and need an advice,
Thank you. Sam

 

[NOMADIC_LJ]

Because you have a stick and drive hwy I would choose 4:88

It will help mpg a little as it puts the power band closer to stock with your larger tires. It will also keep your RPMs a little lower so that will also help with fuel (slightly). Only downside I see is it will give you less torque than the 5:13's.

It's a trade off and you will ultimately have to decide where to make the balance work on both sides for you. Good luck!

 

[JPK]

Weights an issue for performance, but the 35" tires are the main contributor to lost performance.

Most gear ratio charts and formulas would point you toward 4.88's. Here is a link to a site with both a chart - but read the description, its not a JK only chart and assumes a 1:1 transmission ratio - and formula. http://www.4x4offroads.com/gear-ratio-chart.html

However, when you look at the weight you added and the trailer, I'd have to go 5.13's. Also, I have driven a manual trans, 5.13 geared JKU with 35" tires and similar bumpers and winch weight, with no trailer behind it and I thought it drove well.

There are lots of mixed reports on the effect of re-gearing on milage. Many report improvements, some no change. I don't recall any that resulted in a significant drop that couldn't be explained by the simultaneous addition of taller tires or more weight.

My JKU has a Hemi, 37's, auto and as much added weight as yours or maybe a little more. I have 4.88's and think 5.13's would be better.

If fuel economy is the over riding concern, go 4.88's, but if drivability is the number one concern go 5.13's. I haven't heard of anyone complaining about too short gears, only about to tall gears.

JPK

 

[MuleShoer]

4:88s will be a good choice, 5:13s will give you other issues. Gear choice is always a compromise

 

[Ryanc]

Im running 5.13 on a fairly heavy JKU and drives very nice. The 4.10 was brutal. With the weight of your vehicle and the trailer that is what I would consider. Now with 5.13, and if you have an after market driveshaft you can run into tcase issues. As far as gas milage, mine stayed around the same. But who buys a Jeep and worries about gas milage

 

[Dools]

If you see 37's in the future go 5.13, if you think 35's are the largest you are going, stay 4.88's. Even 37's with 4.88's would be good.

Nice trailer by the way. Just finished building mine!

 

[bob91yj]

What issues do 5.13's cause in the JK's? I went with 5.13's on my '05LJ (metric 35's), happy with the decision.

 

[Ryanc]

5.13 in combination with a double carden driveshaft, with a 3+ lift=transfer case detonation. It is difficult to get the pinion aligned correctly and still keep it driveable.

 

[xj joey]

It all depends what you want to do. 4.88 will be better on the street. 5.13s with 35s will be overkill and will break axle shafts if you wheel it. Buddy ran 4.88 on 37 mtr kevlars with great on road power but upgraded to alloy shafts for rock crawling. I would run 4.88 if keeping under 37 tires and more driving then wheeling.

 

[shovelbill]

4.56 will put you close to stock going from a 33 to 35.....with all that weight i would go lower to 4.88. the pinion size is getting smaller as you go to a lower ratio also.

Ryanc....i'm having trouble understanding how a gear swap will affect the pinion angle if it works ok with 4.10's......what does an aftermarket drive shaft have to do with the transfer case blowing......the TC becoms the weak link?

 

[Explore]

having run both 4.88 and 5.13 with my 35's, with a manual I would absolutely go with 4.88. keeps it all in perspective.. handles closer to stock..

my .02

 

[bob91yj]

5.13 in combination with a double carden driveshaft, with a 3+ lift=transfer case detonation. It is difficult to get the pinion aligned correctly and still keep it driveable.

I'm baffled, what does the gear ratio have to do with the pinion angle?

 

[F5driver]

I have a similar setup. I'm running 5.13's with a manual tranny. Lower gearing works better towing the trailer especially at altitude.

 

[Ridge638]

I have an auto trans so my opinion may not count but the 5.13's are perfect for mine with close to the same set up and trailer weight as you have. I have talked to those with the manual trans. and 4.88's who wish they would have done 5.13's.

 

[cwsqbm]

I'm baffled, what does the gear ratio have to do with the pinion angle?

The higher the number, the faster the drive shaft has to spin for a given speed. Overdrive transmissions mean the driveshaft is spinning much faster than engine rpms, and any vibration will become amplified.