2008 rubicon/auto.. Gearing change needed????

My JK had new Dick Cepek LT315/70R17's (tires and wheels) on it when I got it from the dealer. I have read thru some of the older posts on the subject. I have the Super Chip programmer programing in the computer now and it has helped. Got the speedo corrected. As the other thread mentioned - cruse control sages about 5mph. These tires are about 33¼/½" tall as apposed to around stock of about 29"? I regularly pull a utility trailer around (with drop gate). It is big enough I have gotten brothers Arura on it to haul to the dealership when it quit once, and couple other cars for one reason or another. Is a single torsion axle, 12ft long. Thing is, at highway speeds, the Jeep won't shift out of 2nd with the "gate" up, empty. **** If I go to 4.88 gears, am I close to what the stock gearing would be with these tires? Or 5.13's? Pulling the trailer - gas milage is low 10's. Without, highway - is around 14mpg. Using 89 octane, running the "91" program on the chip. Non-ethenol fuel. Thanks for your thoughts, input. (Or does anyone make a super charger/turbo charger for the 3.8?)

From what I've read, a super charger/turbo charger isn't really worth it compaired to a gear change. I would at least go 5.13's. I did the 5.38's and I love them. It feels like a totally different vehicle.

Stock tire diameter for a Rubicon is 32 inches. The Sport (X) came with 29 inch tires and could be upgraded to larger 32 inch tires.

If you're running 33s, the 4.88 on the auto would get you back to a "stock" feel and the 5.13 would give you some pep and would be recommended if you ever step up to a larger tire (35+). I'm not sure if running a higher programming on the Flashpaq versus the octane gas you're running is helping any.

RIPP makes a supercharger kit for the 3.8L which seems to be a very solid kit.
http://www.rippmods.com/2007_2009_Jeep_Wrangler_JK_V_3_Si_Trim_Intercooled_p/0709jk-sds-01.htm

315/70r17 is about 34.5"x12.5". mine measure 34.25" tall at 35 psi on my 4 door. Some might say that pressure is too high but feels right on my rig.


I have 4.88s and they brought me about back to stock performance. a little better at lower speeds, but on the hwy its a pig. but it was a pig with 32" stock tires too. If i had the $$ I'd do the supercharger. it won't help alot for crawling, but on the highway, it should help quite a bit. not sure about towing though. the 3.8 is weak.

Yeesh. That supercharger's already got you up to half the price of a hemi swap, doesn't it?

Thanks all for the above input. Since I am primarily road use, daily driver, gas mileage is of some importance, but that I also pull a trailer regularly, and need to do it well, your thoughts on the following....(Oh - and thanks for the RIPP link too) : RIPP has the long tube headers, does anyone have/use them? Am considering them and a performance exhaust, so..., if I go with 4.88, 5.13, or 5.38 gears - any clue where my gas mileage will be. Guessing - the 4.88's, and maybe 5.13's things may be better than now - with trailer, maybe with out too. 5.38's - ??? Maybe where I am now? But with much better power to the wheels? I am leaning to the 5.13's or maybe the 5.38's. I do not expect to go to taller tires. I don't expect to do much off-roading, but may someday - when I find the time, and/or somewhere to go (I work 6 days a week, run a bussiness). *** Next year, I hope to be able to budget in the RIPP Supercharger. *** Hemi swap would be nice, don't see it happening at this time though . ** Oh, also the Flashpak - I'm running 90, not 91 - mis-print. I ran the 90 gas a bit, and dropped to the mid-grade 89 (all non-corn fuel) and haven't seen any difference.

One other thing... Any preferred brand of gears? And where to get? Have looked so far at Northridge, but have only just started looking. Overhaul or install - kit? Whatever that difference is. <9k miles on the Rubi. <1k with these wheels/tires.

There are a few guys on here that can hook you up with gears. Talk to Redneckhouston.

People have had good luck with Yukon and Superior. There are a few others as well.

If gas mileage is a factor, you're already in the wrong vehicle But if you want to tow, too, and run oversize tires, etc, that's going to have to take a back seat.

I know lots of guys with similar setups that went 5:13's and wished that they had gone with the 5:38's. I have the same exact tires as you. Overdrive was useless with the tires/lift. I towed a small enclosed utility trailer to Colorado with the rubi in complete stock form. Let me tell you, it sucked. The trailer is an aerodynamic unit and with the payload it was about 1500lbs. When I was in Kansas and heading into CO, the headwinds were so strong that I was in 2nd for some of the climbs up slight grades.

This is a good thread to read. Soak it in! http://www.jkowners.com/forum/showthread.php?t=8270&highlight=gears

One good excerpt from the thread: "Now, the second thing. The Auto has an INSANELY deep overdrive compared
to the stick. Run this number. A Rubi, 4:10 6 speed with 35s rolling
down the highway is 40 rpm(yes, 40) less than an Auto with 5:13s and
35s."