So I'm eventually going to go with 35x12.5's for my next set of tires and wondering what the best axle ratio would be. It's auto and right now I have 33x12.5's with the stock 4.10's that come in the Rubicon and the Jeep already seems like it doesn't want to get out of it's own way. I drive it daily and it sees the interstate. I also live at 9,000 feet above sea level so just being here, you lose 30% of your power due to the lack of oxygen in the air. What do you think? 4.88's, 5.13's? I'm kinda leaning for the 5.13's at the moment. Also, if you have 35's and 5.13's, approx how far off would the speedo be?

 

At 9,000 feet this might be a better home for 5.38s. As for the speedo being off, you need to have something to fix it as your shift points are determined by speedometer, rpm and throttle position. Without speedo re-calibration, your transmission will be hunting for gears, costing you both efficiency and performance.

 

9,000 feet is key here. You can throw out what makes sense at much lower elevations. Where someone can maintain speed at 2200 rpm at sea level, at 9,000 feet you are looking at 3,000 rpm to produce the same power. Add in the weight of 35s, and whatever else might get bolted on and you really need to twist that motor to produce enough power to keep it rolling. Then you have the mountainous terrain to roll over.

That's why a gear swap to 5.38s makes a lot of sense and your still likely to see the occasional OD to 3rd to 2nd downshift.

 

4.88 if you're happy with the power now; otherwise, 5.13. I have 5.13s and don't regret it. It keeps the overdrive useful in the hills.

 

I would say 5.13 but if you plan to stay at such a high elevation I would consider 5.38 with the auto.

 

Here is a formula for hp loss at altitudes above sea level:

hp loss = (elevation x 0.03 x hp @ sea level) /1000

9000 X 0.03 X 202 divided by 1000 = 54.54 hp loss.

Or:
Lose 3% for each 1000 feet.
9 X 3%= 27%
202 - 27% = 147.46, a loss of 54.54 hp @ 9000 feet.

The above will give estimates, only. It doesn't take into consideration barometric pressure, air temperature, relative humidity, etc.

 

With the elevation i would go with the 5.13's

 

x2 I would say 5.38's to give you a little more power, maybe 5.13's but trans will still be downshifting, heck mine sometimes does it now with 5.13s and I'm not at 9000ft

 

Just go with Rockwell axles and 6.72 gears.

 

LOL! Good one Redneck! Thanks alot for everyone's input on this!