Automatic Transmision

 

4.88 or 5.13

 

Depends what you use your jk for. If it's your DD, I say 4.56 IMO

 

Forum members are going to need more info about your rig and what you intend to do with it before they can be much help. The difference between the 3.8 and 3.6 engine are big factors in what to recommend.

 

Most are FS rigs so with the 3.6 auto and 35" I like the stock 4.10. On the 3.8 it would be 4.88 or 5.13. Any higher on the 3.6 and you run high rom on the interstate. I regeared a 2013 on 37" to 4.88 and I regretted it. 2800 rpm at 75 mph. I also live in a flat coastal area for reference. I'm putting 37" on my 2007 auto and will be going 5.13.

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Matt, you recommending 4.10s for 37's with 3.6 for non-mountainous terrain? You got me thinking... new tires due in February...

 

Its 3.8 Engine and i live in Puerto Rico too many hills and i use the Highway too im looking a happy médium

 

I've got 5.13 gears and am running 315x75x16 tires at around 5,000' altitude. those gears are just right at this altitude, but I would think that 4.88 would be your best bet. that tire size actually only measures about 33" and I suspect that most "35s" are going to measure about the same actually. with my set-up I'm running right at 2500 rpm at 70 mph. I have a superchip tuner running the 87 octane tune and the speedometer is corrected for the gears and actual tire size. with the larger tires additional rolling resistance I think this gearing is about right.

 

For me, yes. I was much happier with my 4.10 than I was with the 4.88. The pick up was a little better but the interstate was awful. Felt like I was raggin out the engine to do 80. I will take lower pick up for 2200-2400 rpm in the highway. My preference. It crawled identical at gulches to me. Couldn't tell a difference.

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