huskerjk7

I have a 2007 6-speed Rubi with 3"ft lift and 35" tires. Im looking for gears to get my 6th gear back so I can drive it back and forth from the trail with a little more grunt on the trail. Is this the way I want to go? I have heard that the 5:13's get the rpms up too high on the highway. Thanks in advance for any help or guidance you can offer.

Ryno

The consensus of the forum is that if you have a 6-speed then 4.88s are the best choice and will bring you closest to stock RPMs when running 35" tires. You might even see a little performance boost over stock.

JulietKilo

What are your RPMS in 6th gear with 35's?

With the stock rubi tires I am seeing 2500 at around 70 mph. This IMHO is too high stock! I want to see it below 2000. My mpg sucks on the highway, usally around 18 mpg. I have the 4.10's and 32's by the way. My thinking is if I get a 305 or 315 tire I should be right where I want to be in 6th gear. HINCE I am not regearing.

What do the other rubi or 4.10 with 35's think?

huskerjk7

Well......Ive had it over a year and it only has about 1900 miles on it so I havent done much watching of the tach but I know last time I went on a trail ride about 2 hours from home, it seemed to have no 6th gear strength and i was getting uber-poor mileage.

Mini-me

35's with 4.10's 6th gear is absolutely worthless.

I have 5.13's / 35's and my RPM's are 2800 at 65. I get 15 mpg doing a combination of highway and city driving. The jeep has the aerodynamic efficiency of a brick stock. Lifted you have more weight to accelerate and parasitic drag. Fuel economy is not a strong suite of the JK or any lifted vehicle.

Ryno

I, for one, wouldn't be too upset if Jeep actually used a wind tunnel in designing the Wrangler. The windshield could be slanted back several degrees and it would still look good. I know the design is supposed to be upright and militaristic, but with $4/gallon gas, I think most of us would appreciate a couple more MPGs that would come as a result of a Jeep designed with aerodynamics in mind.

Doc_D

Lugging the engine is bad. My S2000 turns 4,500 RPM on the freeway and get s 27 MPG all day long. Granted that motor (9,000 RPM redline) is designed for that, and LOVES running around at high RPM.

But you having your revs too low will hurt fuel economy just as much as having them too high. For every motor there is a sweet spot. Besides that, having your revs too low is hard on bearings and causes high cylinder pressures. I'm guessing staying near the stock RPM will end up getting you the best mileage and won't beat your bearings to death.

I'm holding out for someone to come out with 4.56 gears which on 35 inch tires should put the revs to almost exactly the same place that 4.10s do on 32 inch tires.

JulietKilo

Ummm.. you know they sell jeeps with 3.21 gears and 32" sahara tires right. Tell those guys there RPM's are too low.

Rebel Heart

Just purchased 4.88s w/ 6 speed and 35s. My Rubi sucked after the the 35s with stock 4.10s. Looking forward to a 6th gear and some extra off the line.

JulietKilo

Using this calculator http://www.csgnetwork.com/multirpmcalc.html

4.10 Gear
32 TIRE
70 MPH
.84 Final gear (6th gear)

I get 2531 RPMS, which is what I had said before.

USing all the above except for a 35 inch tire gave me 2314 RPM's. So I would not go with a deeper gear the way I drive.

Using all the above except for a 3.21 gear gives you sahara guys a final of 1982 RPMs with the manual tranny, its even lower for the auto due to a final gear of .69

I am not sure where you read this stuff about bearings and high cylinder pressures... but that is not a problem with these engines. In fact those are problems with forced induction engines...


EDIT: There is a reason Crysler puts those numerically lower gears in there. Its for better gas mileage. You want highway rpms low for better fuel economy plain and simple. There is no damage to an engine from running rpms lower!