This might help. Gear Ratio and Tire Size Calculator - 4x4 and Jeep Ring & Pinion

 

That table is for a 1:1 transmission ratio.

The numbers do not apply to the 4th gear in a 07-11 automatic, 6th gear in any manual JK, or 5th gear in a '12+ automatic.

There are tables in the FAQ sticky at the top of the Modified Tech section that have actual rpm levels by transmission type.

 

You're not serious are you? The chart still gives a baseline of the changes in rpms for given gear ratios. The 5spd auto and 6sp manual and about identical at .83/.84 final drive ratios respectively. I didn't think simple math caculation explanations were necessary.

 

I have a 2012 JKU Rubi with 5:13's and KM/2 37's,.
Its got decent acceleration and can cruise at 75mph without being to buzzy or working too hard.
But it just feels a little short sometimes.
There are many long and steep hills in the Pacific Northwest were I live, so the extra acceleration and gear reduction can be a bonus.

That said I think I would go with 4:88's if I did it again.
I think I would get a little better highway MPG without giving up much performance.

Its up to you, but to be honest its probably a toss up.
Mildly better steep hill performance or mildly better MPG.

Good luck.

 

I have a 2014 JKUR 6 spd with about 1200lbs of aftermarket goods. I'm running 37's with Hutchinson Rock Monster bead locks that weigh 47lbs each. I've been running 4.10's for 2k miles, I'm getting 14 mpg in town and 17 on the Hwy. 6th gear does not exist unless your going downhill, 75 mph is the max speed unless you don't mind running at 3500 rpms in 5th gear. I'm installing 5.13's as we speak and will pick it up on Tuesday of Wednesday. If I had an auto, I would have gone 4.88. If you have a built jeep you'll want to go one gear size lower than the chart says if you want to get back to stock performance.

 

Well I have a 2012 2 door non Rubicon

I very recently replaced both axles with Dynatrac's in preparation of going to 37's

I went back and forth between 4:88's or 5:13

My Jeep is driven 3 or 4 times a week but not very far, I do have the occasional 300 mile road trip, so it's a mixed bag of priorities gear wise

My JK came with pathetic 3:21 so I erred on the side of caution so I went with 5:13's

I'm not sure how it drives as my overhaul was complete except for driveshafts which I'm having custom made at a local shop, I hung out there on Saturday and got to watch the guy building my drive shafts

I should have them on by Tuesday or Wednesday and I'm anxious to try out the new gear ratio

Matthew

 

Most people don't read the details that those numbers are 1:1, and few know the final gear ratios for their transmissions.

Sadly, many can't do simple math either. They fear extraordinarily rpms or think their top speed will be limited with lower gears.

That is why these were created:

 

currently on 4.56's and love it. great combo.

 

That's what I'm leaning towards. Good to hear the 4.56 are good to go as I do like knowing I can still go 80-85mph no problem

 

Just got my jeep back with the new gears, 5.13's. Couldn't be happier with this choice, with my setup, this brings me back to just a bit better than stock performance. I can see how any gear will make you happy. I probably would have been happy going with 5.38 too. My advice is if your on the fence, go to the lower ratio (higher number). Thinking 4.56 and 4.88, go 4.88. Too close to tell the difference at hwy speeds, the difference is in the torque. With my 5.13's I can easily go 80 mph and the rpm's were at 2900 in 6th gear.