Re: Tire Size and Gear Ratios [Archive] - : Jeep Wrangler JK Forum

: Re: Tire Size and Gear Ratios

04-07-2008, 11:50 PM
I have an 08 Rubicon Unlimited, automatic. Im starting the following modifications. RE 4 1/2 Long arm kit with front and rear drive shafts. Warn front and rear rock crawler bumpers with tire carrier. Warn rock sliders, 9.5 ti winch. Procomp 7028 17X8.5 wheels and Procomp Xtreme M/T's. My intent is to do mostly trails and some rock crawling. I want to be able to get out of trouble but I'm not looking so much to get into it. This is not my everyday driver but I will be driving it to offroad destinations.I can't decide between 35 or 37 tires. Rubi is stock with 4.10 gears and D44s front and rear. Can I live with stock setup or should I go with Superior 4.88 gears? If I go with larger gears will I have to change the carrier and lose the stock electric lockers?:confused:

04-08-2008, 05:58 AM
35's with the 4.10's seems to be ok for offroad, but sucks on the hiway if you have any hills to climb. The 4.88's would be much better with 35's and 5.13's for 37's. No carrier change needed.

04-08-2008, 08:47 AM
4.10's work just fine without the OD. If you want OD then you will need to change gears. I have that set up and the OD kicks on and off all the time. usually I just turn it off.

04-08-2008, 10:01 AM
I'm running 35's with 4.88s and think the setup is pretty good. If anything, I would probably go with lower gears rather than higher but find this combination to be just about right for both highway and offroad.

If you go with 35's you might want to consider a short arm kit rather than a long arm kit. A 3" or 3.5" lift will clear the 35's and the short arm versions are quite good at that height. You'll save some money and won't have to cut your original bracketry off. Just a thought.

04-08-2008, 11:24 AM
I'm running 35's on the 4.88 as well. Like gcg says, it's a pretty good setup, runs very good on and off road.

I've also got a set of 37's that are my showoff wheels, and while the Jeep looks tough as hell with them on, it's a dog both on and off road. I'd go to 5.13 if your looking to put 37's on.

04-08-2008, 02:31 PM
I run 4.88's with 37's and they are just fine. I went with 4.88's as they are a little stronger than the 5.13's, but there are plenty of people running the 5.13's with no issues.

The 5.13's will help a little with performance, especially in hilly terrain. In reality, although there is a performance difference, there isn't much of one. At 70 mph, auto transmission and 37's, you'll be pulling the following RPM's:

4.88 - 2140
5.13 - 2250

That's 110 rpm difference at 70 mph, with 35's it's only a little more, about 116 rpm difference. Granted it is at at the beginning of the power band, and you'll be a touch quicker off the line, but at the end of the day it's not much of a difference.

If you recalibrate the speedo, the shift points will be good. If you use a programmer, you'll pick up some performance that way too.

With an auto (excluding any TC doubling) you are looking at crawl ratios of:

4.88 - 55
5.13 - 58

With a stick you are looking at:

4.88 - 87
5.13 - 91

Again, not a significant difference.