Re-gear time need advice

[Stroked 550]

I have a 2011 JKU auto transmission on 35s

I live at 6500 feet so everyday Im driving up and down mountains
I go offroading a couple times a week

Right now the jeep is a complete dog, it bogs down to 35 mph going up hills

What gear ratio do you recommend I run?

I want to run a high quality Ring and pinon kit, what brand do you recommend?

 

[Jeep or Tacoma]

What is your rear end now? I put 175000 on my 08 3.8 jlur with 410 rear end and 315 70 17 . I towed a trailer all the way up the coast highway. It did pretty good. In my 2018 jlur it has 410 3.6 and I run 315 70 17. No
Problem at all anywhere the 8sp makes a huge difference.
If you have a 373 now I would look at 488 if it’s a 321 then 456 would probably. Be good.

There is a formula running around some where where you can calc the final drive ratio put in your gears and tire size rear end etc. figure out what you have now redo the calcs for a newer jlur running 410. See what you get then do yours again with varying the rear end ratios until you get close to a new jlur with 410. Iam guessing 456 is gonna be your final answer

 

[vtsoundman]

4.88 or 5.13 for auto with 3.8 and 35s.

4.56 or 4.88 for 3.8l 6sp and 35s.

Elevation = more gear.

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[BulldoginaJeepwithaColt]

4.88 or 5.13 for auto with 3.8 and 35s.

4.56 or 4.88 for 3.8l 6sp and 35s.

Elevation = more gear.

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What he said..

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[wADVr]

For 35s I’d say 5.13s but what are your future plans? 37s? Hemi? those two possible plans need the opposite gearing so plan ahead.

go Dana/spicer if possible always

I ran 5.38s on 37s for 10 years and over 200k. Thought several times that dropping the tires to 35s with those 5.38s would be a huge improvement but never did. I personally think the v6s like to rev and need higher rpm to make MPG and sustainable hiway speed without constant down shifting.. look at the 2012-2018JKs much less OD gear and higher hiway rpm. Just my opinion.

 

[Stroked 550]

Right now it has stock gears......it is a struggle going up the mountains here

My future plans would be a hemi but that most likely is 2-5 years down the road

I am going to stick with 35s for the considerable future they're plenty tall for the trails I go on and this rig is my daily driver

I agree I think that the engine runs better at higher rpms and it will prevent all those downshifts it has right now

 

[vtsoundman]

Right now it has stock gears......it is a struggle going up the mountains here

My future plans would be a hemi but that most likely is 2-5 years down the road

I am going to stick with 35s for the considerable future they're plenty tall for the trails I go on and this rig is my daily driver

I agree I think that the engine runs better at higher rpms and it will prevent all those downshifts it has right now

Hate to say it, but the 3.8 will struggle regardless of what you do...mtns or otherwise.

The JK is a heavy platform and modern engines systems have changed our perception of acceptable/need. The JK platform started it's life as an under powered platform (as compared to other similar sized vehicles at the time). The auto in the 07-11s with its wide gearing and sub-optimal shift programing - makes it worse.

The gearing will help get the motor to operate in a better power band. Follow my recs above - it will restore/move the rpm/mph powerband to a more appropriate point.

There are people that claim the 4.0 is better - it isn't. It's worse. The tires the 4.0 motor spun and Jeeps it powered, were lighter/smaller/less surface area. Is it more reliable? Probably b/c it is simpler.

The 3.6 is a better motor only in that it has more power with a slightly different power curve. More reliable? Maybe...maybe not (I'd venture to say it isn't, the 3.8 is a simpler motor).

The 3.8 JK/JKU Jeeps require a slower pace/slower highway speed expectation...the gears will make a big difference and restore proper operation, but will not never be a more powerful platform.

I say all of the above to help align expectations - I sometimes have to remind myself of the above...and ask, is it worth the cost/time to get rid of my 07 and all its mods/custom built equipment. The answer is usually, 'nope at the moment, it does what I need just fine, just a little slower. I can use the ten of thousands on other, better ways.' And then I smile as I pop it into 4wd, get onto the trail ...and then arrive at camp for the night....the thousands I've saved lets me get out sooner, longer, and spend more time with my son, family, or friends...

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[billiebob]

35s get to the point a regear makes sense but your issue is altitude. Sure a regear will make things a bit better but you need sea level air first. Look at a supercharger.

Someone asked what gears you have. We need the numbers, not "stock". There were several choices.

edit
Just noticed, you are considering a hemi, I'd bet at 6500 feet a supercharged V6 would pull as hard as a non supercharged hemi.

 

[Stroked 550]

35s get to the point a regear makes sense but your issue is altitude. Sure a regear will make things a bit better but you need sea level air first. Look at a supercharger.

Someone asked what gears you have. We need the numbers, not "stock". There were several choices.

edit
Just noticed, you are considering a hemi, I'd bet at 6500 feet a supercharged V6 would pull as hard as a non supercharged hemi.

It would be hard to find out what gear ratio I have without taking it to a shop

yeah I am considering a hemi swap but if a supercharger would make it pull as hard a stock hemi I would do the charger route

If I do a supercharger are there any other mods I can do to get me to the 300hp range?

 

[Jurfie]

It would be hard to find out what gear ratio I have without taking it to a shop

Not really. Lift the rear, spin a tire and count the number of rotations of the driveshaft. +3 times = 3.21s and +4 times = 4.10s. I'd bet you are running 3.21s unless it is a Rubicon.

 

[billiebob]

Or, key in your VIN number on the Chrysler build sheet web page and get all the specs.

FCA RAM

fcacommunity.force.com

Or, as Jurfie says, ....

I do it a bit different,
Lift one tire
Tape a string to the driveshaft.
Rotate the tire EXACTLY 2 revolutions, use a chalk mark on the tire and driveway
Count the number of string wraps

4 full wraps plus a bit.... 4.10 ratios
3.75 wraps............ 3.73
3.5 wraps........... 3.50
3.25 wraps..... 3.23
3 wraps ... 3.07

 

[Jurfie]

Or, key in your VIN number on the Chrysler build sheet web page andget all the specs.

But as Jurfie says, ....

I do it a bit different,
Lift one tire
Tape a string to the driveshaft.
Rotate the tire EXACTLY 2 revolutions
Count the number of string wraps and divide by 2

8 full wraps plus a bit.... 4.10
7 full wraps..... 3.50 ratio
6.5 wraps..... 3.23
6 wraps ... 3.07

Good trick; I haven't seen that one. Also, I forgot about the build sheet lookup by VIN page; I've used this one in the past: https://www.vindecoderz.com/EN/Jeep

 

[Stroked 550]

i tried both of those websites and they say no record found lol just my luck

 

[Little Foot]

Regear is absolutely worth it...regardless of elevation. Yes the motor won’t get any more
powerful as everyone is pointing out...but you are multiplying the amount of torque being applied to the wheels and therefore it’s going to be a lot easier on your engine and transmission going through the hills. Don’t worry about power upgrades just yet. Just regear and you’ll be surprised the transformation in driveability with those big tires. As far as what gear ratio I would lean towards 4.56 for a 35. Assuming you have 3.73 gears, a jump to 4.10 isn’t much at all and not worth the money. Then factor in elevation and 4.56 seems to me the minimum. The next jump to 4.88 is a good option too and properly a better option considering your altitude and constant hill climbing. As far as 5.13 I feel like that’s a bit high for 35’s but I’ve only driven JKs at street speeds and briefly on the highways so I’m not sure what RPM that places them at cruising. I’m also at sea level and the highways are relatively flat so my experience will differ greatly from yours in that respect. (I work at a custom Jeep shop so I drive JK’s and JL’s everyday, but only test drives for drivability issues).


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[vtsoundman]

Regear is absolutely worth it...regardless of elevation. Yes the motor won’t get any more
powerful as everyone is pointing out...but you are multiplying the amount of torque being applied to the wheels and therefore it’s going to be a lot easier on your engine and transmission going through the hills. Don’t worry about power upgrades just yet. Just regear and you’ll be surprised the transformation in driveability with those big tires. As far as what gear ratio I would lean towards 4.56 for a 35. Assuming you have 3.73 gears, a jump to 4.10 isn’t much at all and not worth the money. Then factor in elevation and 4.56 seems to me the minimum. The next jump to 4.88 is a good option too and properly a better option considering your altitude and constant hill climbing. As far as 5.13 I feel like that’s a bit high for 35’s but I’ve only driven JKs at street speeds and briefly on the highways so I’m not sure what RPM that places them at cruising. I’m also at sea level and the highways are relatively flat so my experience will differ greatly from yours in that respect. (I work at a custom Jeep shop so I drive JK’s and JL’s everyday, but only test drives for drivability issues).


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Regear is absolutely worth it...regardless of elevation. Yes the motor won’t get any more
powerful as everyone is pointing out...but you are multiplying the amount of torque being applied to the wheels and therefore it’s going to be a lot easier on your engine and transmission going through the hills. Don’t worry about power upgrades just yet. Just regear and you’ll be surprised the transformation in driveability with those big tires. As far as what gear ratio I would lean towards 4.56 for a 35. Assuming you have 3.73 gears, a jump to 4.10 isn’t much at all and not worth the money. Then factor in elevation and 4.56 seems to me the minimum. The next jump to 4.88 is a good option too and properly a better option considering your altitude and constant hill climbing. As far as 5.13 I feel like that’s a bit high for 35’s but I’ve only driven JKs at street speeds and briefly on the highways so I’m not sure what RPM that places them at cruising. I’m also at sea level and the highways are relatively flat so my experience will differ greatly from yours in that respect. (I work at a custom Jeep shop so I drive JK’s and JL’s everyday, but only test drives for drivability issues).


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Hold the phone...

This is a 3.8 with an Auto in the mountains.

Not a 3.6 with 5sp or a JL with 8sp....

4.56 is a total waste of money. 4.88 is min for low elevations...5.13 is my firm recommendation for the OP. It will take sometime to run the proper google searches looking for 07-11 Auto 3.8 at elevation, but you'll find 5.13s are the preferred gear. Some even went to 5.38s! (But I believe that may be a bit excessive).

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