Originally Posted by OutlawJoker

This may seems like a stupid question but i was wondering what the difference was between the 4.88 reverse and the regular 4.88's? I am certain i will need to regear and since i know exactly sqwat about gearing i don't know what to order. When i look them up they always ask for reg. or reverse. Will i need to by gears for both?

Originally Posted by nthinuf

'JK' D30's and D44's use different gears than non-JK 30's/44's. When you are looking, just be sure it clearly indicates for JK axles.

Originally Posted by JeepAddOns-Chris

Pretty much. For a front axle, low pinion standard cut is weaker than a high pinion reverse cut. Essentially a standard cut is great for rear axles, but think about that axle and flipping it around front. Then essentially you're traveling on your coast side which is not as strong. This is why TJ guys frequently will swap the TJ LPD30 for an XJ HPD30 and why the Ford Dana 44/D60 front ends are a more popular swap than some others (Dodge/Chevy are standard).

Originally Posted by Moraespedro

How about the strength of a 5.13 gear and dana 30? I'm buying new gears and I'm really confused about 4.88 x 5.13...
To make things clear, I have a 2007 sport (X) auto 2dr, open front dif... Running 35 now... maybe, with little chances, 37s in 18 months... Afraid of 37 + dana 30 + cost to strength it here (I live at Brazil...)...

I've read about the poor strength of this combo, 5.13 and dana 30, but no one is saying anything about it here...

Originally Posted by JPop

Vehicles aren't manufactured on the whims of Engineers alone. You have marketing people aiming for EPA estimates and business people wanting to use bin parts to reduce costs. A lot of strings pulling at what creates the final product, and you don't need to look any further than Daimler looking for a suitor, and the only one they could find was Cerberus, a private equity firm with no real automotive experience. Chrysler was leveraging their brands to produce sales and their only success story was the Hemi, which was soon to be thwarted by rising fuel costs.

EPA estimates are just that, estimates. If you want mass market appeal, you need to have some decent numbers on the window sticker. EPA estimates are definitely a marketing target, and through 2007 they weren't even close to a real world measure of economy. For instance highway fuel economy was estimated using an average of 48mph and a top speed of 60mph. If engineers are driving that bus, they are aiming at real world results at 70mph and a sustainable amount of overhead so the vehicle doesn't need to kick down for moderate grades.

Horsepower is simply torque applied over time. They will always have a direct relationship. Horsepower = (Torque x RPM) / 5252. Torque is like a hammer, determining the rate of acceleration while horsepower is like a come along which determines a vehicles ability to maintain speed. Torque is certainly nice to have, but if I hit peak torque at 1200 rpm I would need some crazy numerically low gear set to apply it at highway speeds, while also having diminishing returns by increasing rpm.

Lifting a vehicle and applying larger tires has many things that increase it's need for power to maintain cruise speeds. Increased drag, Increased frontal area of vehicle, Additional weight, Increased tire rolling resistance, Increased speed effect of tire rolling resistance and Increased rolling load. Moving from a 32" tire to a 35" tire with a lift can require 15 or more additional horsepower to maintain highway speed. Note, we cannot use torque to determine what is needed to maintain speed because there is no element of time. Torque can move our 2 ton vehicle, but you need the element of time to determine if it's going to move an inch, a foot or a mile in a minute. The easiest way to get the additional power is by increasing rpms, be it by downshifting, turning OD off or running a numerically higher gear set.

Certainly there is a very small minority who think you can get this done running at a lower rpm. My personal experience, which very much coincides with that of planman, has demonstrated that I can't maintain 70mph on a grade as insignificant as an overpass with 35s at much less than 2300 rpm, operating at 600' above sea level. Steeper grades with my 35s while still not getting above 3% and I need to downshift. Most of all, I see little to no difference in efficiency running at 2700 as opposed to 2300, allowing the throttle blade to regulate power. Now move to an automatic transmission where you have the extra caveats of unlocking the converter then flashing your rpms as much as 50% higher, and you can quickly realize it's not going to take a lot of occurrences to quickly eat up any benefit of lower rpm cruise speeds.

Originally Posted by Dronac

IIRC, the new 2012 auto's are geared lower in the transmission, and have a higher output engine. If nothing was wrong before, why lower the ratio after adding the Pentastar? My parents just got a new Pentastar powered Caravan (equivelent to the Town and Country) and it's RPM levels are the same as with their old T&C. I think this showes that Jeep did see an issue with the old 07-11 JK driveline configuration, and took steps to correct it.

Originally Posted by Cervelo

Wow I think we have 1 out of a bizillion here a person who trust the cars companies!!! I can assure you that engineers have the last say in anything related to the American car industry. I think getting our ass kick by foreign car companies over the past 30 yrs and that little issues (what was it) oh yea that bail out thingy is a pretty good indication of the state of affairs. But that's another thread I think! I'm going with J-Pops and Planman and the others who obviously know what their doing when it comes to the mods on my Jeep.