2010 JK Rubicon gearing
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JK Newbie
Joined: Jul 2020
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From: new albany
2010 JK Rubicon gearing
I've been searching and reading past posts today but wanted some input on what to do...
We took my 2010 Jeep Rubicon to the coast for a vacation last week which was the first real road trip for it. I was very unsatisfied with the power at 65-70 MPH. I have LT285-70R17 tires with stock 4.1 gears. I am thinking from my research that I need 4.88 gears to get it back to normal but would like your input. I drive it mostly to work 6 miles each way. Some trails but not often. It has heavy aftermarket bumpers and winch. I will be doing the swap myself as I have changed gears in other vehicles a few times. So... will 4.88 gears get me back to a normal driving Jeep with some power?
Edited...
Automatic transmission.
BF Goodrich Mud Terrain T/A so a fairly heavy tire.
As far as load... it's a 4 door. Light bar. Heavy front and rear burear. Dont pull a trailer with it.
We took my 2010 Jeep Rubicon to the coast for a vacation last week which was the first real road trip for it. I was very unsatisfied with the power at 65-70 MPH. I have LT285-70R17 tires with stock 4.1 gears. I am thinking from my research that I need 4.88 gears to get it back to normal but would like your input. I drive it mostly to work 6 miles each way. Some trails but not often. It has heavy aftermarket bumpers and winch. I will be doing the swap myself as I have changed gears in other vehicles a few times. So... will 4.88 gears get me back to a normal driving Jeep with some power?
Edited...
Automatic transmission.
BF Goodrich Mud Terrain T/A so a fairly heavy tire.
As far as load... it's a 4 door. Light bar. Heavy front and rear burear. Dont pull a trailer with it.
Last edited by jstevenj; Jul 15, 2020 at 02:16 PM. Reason: A
JK Jedi
Joined: Dec 2010
Posts: 5,642
Likes: 486
From: Knoxville
How much weight do you have happening on the jeep? What type/ brand of tires? The 3.8 isn't great but with 4.10's and 33's, you shouldn't have any issues at all. Manual vs auto will also be a question folks will have.
Having the 3.8 and I had 33's on it for the longest time, I think that the 4.88's might be overkill, but that's my 2 cents. Most folks say that moving a single gear set isn't worth it so you'd be on the right track with 4.88's.
Having the 3.8 and I had 33's on it for the longest time, I think that the 4.88's might be overkill, but that's my 2 cents. Most folks say that moving a single gear set isn't worth it so you'd be on the right track with 4.88's.
JK Jedi Master
Joined: Jan 2008
Posts: 11,463
Likes: 165
From: Austin <--> Colorado Springs
Auto or manual? Any thoughts on going to taller tires in the future? 3.8 Auto's generally go one numeric ratio higher than manuals. Do a quick google search on any phrase such as "jeep jk gear chart", there are plenty of them out there floating around on the net.
Since you want to compare to 'normal' performance, you need a baseline, which will be whatever the rpm's at 70 mph were with your old stock tires. (I've never measured stock rubi tires nor have I had 4.10 gears, but you should know...) Once you have your baseline, MEASURE your current tires and plug the number into the chart for your transmission. (the charts use actual measured height, not sidewall or mfg spec!!!)
For a 3.8 Auto, you'll come up with something like this :
4.10 + 30" tires = 2219 rpm @ 70 mph
4.88 + 32" tires = 2476 rpm @ 70 mph
2476 - 2219 = 257. So, with 4.88's and the larger tires, you would be running appx 257 rpm higher than when you drove off the dealers lot. (again, assuming you have the rpm's at 70 from the old tires...)
Since you want to compare to 'normal' performance, you need a baseline, which will be whatever the rpm's at 70 mph were with your old stock tires. (I've never measured stock rubi tires nor have I had 4.10 gears, but you should know...) Once you have your baseline, MEASURE your current tires and plug the number into the chart for your transmission. (the charts use actual measured height, not sidewall or mfg spec!!!)
For a 3.8 Auto, you'll come up with something like this :
4.10 + 30" tires = 2219 rpm @ 70 mph
4.88 + 32" tires = 2476 rpm @ 70 mph
2476 - 2219 = 257. So, with 4.88's and the larger tires, you would be running appx 257 rpm higher than when you drove off the dealers lot. (again, assuming you have the rpm's at 70 from the old tires...)