I have a 08 2Dr auto 2.5" coil lift. 35x12.50 18 federal mt's. Jeep gets driven little. But every so often we take.it 3 hrs away to the beach house. It gets bad gas mileage which isnt an issue. Running down the highway it runs about 2300-2500 RPMs and downshifts Alot. Currently running 3.73's..... What would be the benefits of regearing....also what are the cons of regearing....seems like I wouldn't have highway speeds if I went to 5.13's....also we never take the Jeep offroad. Its just my wifes mall crawler.

 

In a nutshell, the benefits are feeling more power when taking off/accelerating, and improved MPG. The con, is that is of course costs money to get done, but also if you have a D30 in the front, the teeth size on 5.13's starts to get a little small, but for 35's and on road use, it's just fine. You'll still have highway speeds with 5.13 gearing. You'll also want to factor in getting a programmer like an aev procal to let your Jeeps computer know that it has a new gear ratio as well.

For reference, here is a recommended gear ratio chart:

 

You might consider the 4.88's over the 5.13's, being that you have a D30, and picking up a tuner or pro cal to calibrate the tire size which will correct the shift points. In the meantime, keep the overdrive off to help with the gear hunting.

 

So if I get a procal will it help with the downshifting....she has drove the Jeep this way for 2 years which was only 12k miles. I guess im curious as to what its hurting other than the mpg as it is....I don't want anything to tear up on her and me be stuck at work on nights or something

 

Procal will make a night and day difference in your shift points. Do it

 

In your situation it sounds like a re-gear would be a waste of money and to go up to 5.13 would be insane if you want any decent mileage on the highway. You say it's around 2500RPM now which is in the power band for the 3.8 engine (at least on the 6spd it is) I find anything above that and it just sucks back the gas. Get a pro-cal or any programmer that will change your tire size and reset your shift points to be in the optimum range like it was from the factory. I'd just keep it out of OD for now if you want to see how a gear change would affect the RPMs on the highway and to give you the increase in power...so to speak.

After doing this then you can decide if you want to drop $1500-2000 on a re-gear but if you do long highway trips I wouldn't go over 4.56or 4.88 if you do long high speed highway driving. 5.13 are good but mainly for city driving and offroad because it does scream on the highway at high speeds, but not as bad with the auto. We plan on getting 37s and wont go any higher than 4.88 because it is the fiancees daily driver and we do take her Jeep on long trips and want a nice cruising RPM for the highway. I don't want to listen to the Jeep screaming at 3000RPM the whole time for a 6+ hr drive

 

How do you like your Federal Cougra MT's? I was so close to buying a set but my buddy had guard dogs and I liked the look of them so I went that direction.

 

How fast are you going to get those rpm's?

Just taking numbers from the chart above. Using 3.73 and 34" for actual tire height of the 35's, gives 1781rpm @ 70. Is the 2300-2500 OD Off? Or do you cruise up at 80 or 90.

If you do not have a tuner/programmer to recalibrate, your mph (and mpg) numbers are incorrect, so using the chart is just guesswork for now.

 

Normally run at 70mph and it between 2k and 2500. But when it down shifts it hits around 3k. I will try a tuner I didnt know they changed shift points just thought it re did the Speedo. the federals have been good for 2 years. But only have 12k miles on em. Rotated every.3k. They roar but its a mt. 259 a peice.for 35's on a 18 and only drive it a little bit I couldnt pass em up

 

Ordered a aev procal last night