I think I'll try a programmer first, and order a set of 4.88's. I appreciate everyone's input. Lots of good feedback and advice.

Thanks guys....

 

Well I made my first road trip with the 35's today. Went to Hannibal MO. to watch the Grand National WEROCK rock crawling competition, (which friggen rocked!!!) Went the interstate to MO; ran about 70 with the OD off to keep it from kicking in and out. Turned about 2800 at 70. The MPG showed 12.4, it's reading off some because my Speedometer is off by 5 according to my GPS, anyway went through 3/4's of a tank in about 170 miles. Came back a 2 lane and ran 55 the whole way back, the rpm's were right at 2100, the MPG showed 14.6 and only used right at 1/2 tank. The 2 lane shaved a few miles off the return route, but I was wanting to point out the difference in MPG from 2800 to 2100.

Looking to put 4.88's in soon, I hope that this will allow me to run the overdrive and keep the rpms in the low 2K's.

 

Thanks for the update

 

I'm pretty positive you *need* the programmer if you change tires or gears, since driving without your speedo/odo calibrated would provide a false (if even slight) reading on your vehicle's odometer, which as far as I know is illegal.

 

I ordered a Hypertech from Nothridge, I hope to receive it this week.

 

I just put in the Hypertech program today, and I'm getting 5.13's put into mine tomorrow... Too pokey with 35's and 4.10's...

 

This is what I believe, but I have no edvidence to support it.

Most cars have transmissions that have been highly tuned and set to shift at certain points. They also have a highway speed that they can run at with good mpg and this is usually around 60mph.

I think the best way to gear the Jeep would be to consider what I said above and gear for the difference in tire size. If your tires are say 10 percent larger, you should gear down 10 percent. Going from a 31 tire to a 35 tire you go up about 13 percent. If you had 4:10 to start with from the tow package or a rubicon this means you would need a gear ratio of 4.63. Because this doesn't exist and because the bigger tires require more power to turn (efficiency losses due to inertia) 4.88 may be the way to go.

Just talkin' out loud here.

Also...

When you do gear ratio calculations all the numbers are multiplied or divided (no adding or subtracting) and by the laws of math my percentages larger concept should work. I hope this makes sense, if not ignore this comment.

In addition when you go to Future shop to buy a TV, do you look at how many pixels and stuff it has? No you look at the quality of the picture and compare it to the other TV's beside it and you know if its quality is good or not. This is the same for gear ratios IMO. Drive your buddies jeep on 4.56, 4.88 and 5.13's with the tire size you want and see which ones make you happy. Yes I realize this is not an option for everyone on this board.

Erik

 

Im thinkning of the new 4.56 , i know not the right place to post but just though id let u guys know

 

Hey, I'm open minded. It's all about the numbers. I'd like to read about how the 4.56's do.....

 

i agree with 4.56, but 4.88's are better than 3.73

use this chart - the 4 spd auto gear ratios's in my signature

http://www.angelfire.com/fl/procrastination/rear.html