I'm waiting for my RK 3.5" X Factor and Bilstein 5100 to install it on my 2012 JK 4 door and I"m thinking to use 35 or 37 tires. As every body know, I need to re gear. My trans is an auto. I drive between 55 and 65 mph on High way for about 30 minutes, on a City may be 30 minutes more and about 30 to 45 minutes on hills. Two times a day. (90% on road and 10% off road, Mud and Rock Climb).
Based on your knowledge guys, 4:88 or 5:13?
I"m going to appreciate all your support.
I always go back to the "if I knew then what I know now" I probably would have done things differently, but I knew I was going to modify everything on my Jeep, so maybe someone else will find this helpful.
I agree... on the 2012+ auto the 4.88s are ideal for 37s (4.56 for 35s)... but that is on the auto. On the manual I would say 4.88 or 5.13s would be ideal for 37s.
One more thing to consider when regearing is your final crawl ratio, and since you indicate you are not really a rock crawler and do mainly trails and mud, you don't really have to consider the below, but just in case you find it helpful.
Your crawl ratio is easy to figure out, and ideally your final drive or crawl ratio should at least be between 50 to 1 (50:1) and 70 to 1 (70:1) for rock crawling performance.
Transmission First Gear Ratio x Transfer Case Low Range Ratio x Axle Ratio = Final Crawl Ratio
For example, a stock wrangler Sport is 3.59 x 2.72 x 3.21 = 31.35
With 4.88s: 3.59 x 2.72 x 4.88 = 47.65
with 5.13 (which I cannot confirm if this can be done on a D30): 3.59 x 2.72 x 5.13 = 50.09
Now a 2012 Rubicon Auto Stock 3.59 x 4.1 x 4.1 = 60.35
Rubi with 4.88s: 3.59 x 4.1 x 4.88 = 71.83
Rubi with 5.13s: 3.59 x 4.1 x 5.13 = 75.51
The 2012 Manual Rubi’s first gear ratio is 4.46... so right out of the box you are: Stock: 4.46 x 4.1 x 4.1 = 74.97...
With 4.88s: 4.46 x 4.1 x 4.88 = 89.24
With 5.13: 4.46 x 4.1 x 5.13 = 93.81
Just to put the auto and manuals into prospective. You can see that right out the box the rubi's tc 4:1 ratio makes a huge difference for crawling.
However, the crawl ratio is obviously for when you are in 4wd. For two wheel drive operation and daily driving, you don’t have to worry about the crawl ratio, but you do need to worry about rotating the tires with less stress on the tranny. As someone mentioned, the 5.13s would give you your pep back, but running highway speeds your RPMs would be higher than stock. I personally would recommend 4.88s or 5.13s with 37s on the 2012+ manual and 4.88s on the auto for 37s and 4.56 for 35s.
Don't forget you will need a programmer when you change the gears too (I recommend superchips).
I hope this helps… basically you can’t go wrong with 4.88s with 37s and 4.56 with 35s and the 2012+ jeeps with autos.