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Northern Virginia Jeepers Association
November 15, 2018, 10:53:45 PM

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JeepVT
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« on: October 26, 2018, 12:49:39 PM »

Hello!

Relatively new to the forum but was hoping I could get some thoughts on proper gear ratio for my planned build.  I have a 2017 JKU Sport with manual transmission and 3.73 gears and am looking to add the Teraflex S/T2 kit (2.5" coils, Falcon shocks, front adj trackbar, rear relo bracket, bumpstops, and front LCAs) coupled with some 285/75r17s (roughly a 34 x 11.50).  Are my current 3.73s going to leave me significantly under powered?  If I was to re-gear, should I be looking at a 4.10 or 4.56?  I realize power loss is kind of subjective, but if anyone has experience with a similar setup or has any recommendations I would appreciate it.  Thanks!

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Dropkick
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« Reply #1 on: October 26, 2018, 03:54:21 PM »

Either will work. If you think you’ll ever want bigger tires go with 4.56.

Check this chart



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Shamus

'09JKU
ogre45
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« Reply #2 on: October 26, 2018, 04:23:02 PM »

My .02 cents. You will be fine. I've run 35's with 3.73 gears and it was fine. All I did was use a Superchips Flashcal. Re calibrated the speedo and it adjusts the shift points with no other issues.
With my current Jeep I'm running 285/70-17 and have 3.21 gears. It's a little sluggish, but nothing I'm concerned about. The speedo recal is an easy fix and makes a noticeable difference.

Sent from my SM-N950U using Tapatalk


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Alex
1969 Jeepster Commando in work
2018 JKU Golden Eagle,Teraflex leveling kit, EVO oil and trans skid
jrussbowman
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« Reply #3 on: October 28, 2018, 01:28:50 PM »

285/70/17 and running heavy with mods and manual transmission I am pretty unhappy with my 2015 4 door on road. 6th gear is basically useless. I'm probably going to go to 4.10 when I get my tax return.

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Iceman
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« Reply #4 on: October 29, 2018, 07:28:52 AM »

My manual 2013 2 door came from the factory with 3.73 gears. After I put my lift on, I ran 315/70/17 ("metric 35s") on it for about a year and a half while it was still relatively light. It was not ideal but was tolerable. I went with 4.56 when I had my re-gear done this past spring. Night and day difference and one of the best mods I have done to my Jeep.

My 2 cents... gear work is a big investment $$$ in your Jeep (unless you have the skill/time/tools to do it yourself). Jumping 1 gear set from 3.73 to 4.10 isn't really worth it. And this isn't a job you want to pay for twice. I would recommend nothing less than 4.56 if you plan on running bigger tires. Also if you have the funds available, may as well have some type of traction device installed while they are in there.

-Clayton

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JeepVT
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« Reply #5 on: October 29, 2018, 08:42:45 AM »

Thanks to all for the input!  Will the 4.56 gears kill my mileage?  I know it could be a driveway job for some, but any suggestions on a local shop?   

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R3
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« Reply #6 on: October 29, 2018, 10:01:55 AM »

 Running 4.88 with BFG 37 ( really 35s)  I average 17 round town, trip under 65 I get 19.5-20.5, over 65 solid 17.5


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Cheers
RRR
17 JKURR
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37 BFG ATs
Dynatrac, PSC, Barnes, Ried, RCV....
next?

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highlandercj-7
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« Reply #7 on: October 29, 2018, 10:06:41 AM »

I can't see it performing any worse then the 3.8L with 373's and stock tires, worst case scenario.

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HighlanderCJ-7
Iceman
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« Reply #8 on: October 29, 2018, 10:40:53 AM »

Mileage would only be affected minimally, if any, with a 4.56 gear change. Hell it may even improve since the Jeep won't be under geared. It all depends on your driving style. I think it is addition of a lift, weight to your vehicle (ex - steel bumpers, winch, skids) along with bigger tires with more rolling resistance that contributes to gas mileage hits. But hey... who bought a Jeep for gas mileage right?

I had my gear work done by Collin at Quality Performance Group in Fairfax. Great mechanic and knew his stuff but unfortunately he relocated to Colorado. Depending on where you live there are other great/reputable shops in the Vendors section. I am sure others will chime in with their experiences and recommendations of where/where not to go.

-Clayton

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areba32
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« Reply #9 on: October 29, 2018, 11:25:24 AM »

I had this same exact question although that thread got a little out of control: http://novajeepers.net/index.php?topic=28825.msg304746#msg304746

I ended up choosing 4.56 with 35's and it's a great combo. I had 3.21's with 285/70R17's and it felt like a completely different vehicle after the regear. My milage after the regear has been about 16-17 combined and 19-20 highway. If you plan on ever going up in size I would say 4.56.

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2013 JK
4.56 Yukon gears
Teraflex 2.5'' lift
35x12.50R17 Goodyear Attitudes
jrussbowman
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« Reply #10 on: October 29, 2018, 11:53:04 AM »

Those guys are getting better gas mileage than I am with 285/70/17 and 3.21 gears. I drive slow too. Kind of making me hopeful going to 4.10 will be a good fit for my build, I'm not moving up past my 33's on the 4 door. Already decided if I want to build a crawler I'm getting a 2 door.

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karlmagnum
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« Reply #11 on: November 09, 2018, 02:09:50 AM »

I would go with 4.56 so I can fit bigger tires in the future.

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Zedi
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« Reply #12 on: November 09, 2018, 08:40:40 AM »

Either will work. If you think you’ll ever want bigger tires go with 4.56.

Check this chart



Sent from my iPhone using Tapatalk

Is there a similar chart for the 4.0 TJ that instead of showing rpm@ 70 MPH would show RPM in low range at crawling speeds?

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1998 TJ JEEBA Jeep
jdavis2nd
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« Reply #13 on: November 09, 2018, 10:31:05 AM »

Hello!

Relatively new to the forum but was hoping I could get some thoughts on proper gear ratio for my planned build.  I have a 2017 JKU Sport with manual transmission and 3.73 gears and am looking to add the Teraflex S/T2 kit (2.5" coils, Falcon shocks, front adj trackbar, rear relo bracket, bumpstops, and front LCAs) coupled with some 285/75r17s (roughly a 34 x 11.50).  Are my current 3.73s going to leave me significantly under powered?  If I was to re-gear, should I be looking at a 4.10 or 4.56?  I realize power loss is kind of subjective, but if anyone has experience with a similar setup or has any recommendations I would appreciate it.  Thanks!

I had that same set-up for maybe a year. It will work fine but 4.56 is better. I actually went to 4.88 for several months before upgrading to 37's and I loved it.

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zuke
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« Reply #14 on: November 09, 2018, 10:46:18 AM »

Is there a similar chart for the 4.0 TJ that instead of showing rpm@ 70 MPH would show RPM in low range at crawling speeds?

Not that i've ever seen, But this calculator over at Crawlpedia can help you figure out rpm based on a particular configuration;

https://www.crawlpedia.com/rpm_gear_calculator.htm

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John
2017 BU Trailhawk
2015 JK Unlimited Sahara
2008 JK Unlimited
2006 TJ Rubicon
1999 TJ SE
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