Are you re-gearing for 35s or 37s?

[Jeepsk8]

I just installed 35's and adjusted the tire size with a Flashcal. I see no need to regear my JLUR.

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[1quick1]

I've said this before in another thread but my 2018 JLU with 3.45 gears 2.5" lift and 315/70/17's is far faster than my 2014 JK w/3.73's and 33's and this is in CO where I inherently lose some power. This 8spd makes a world of difference and I see no reason to regear. I did pay the dealer $150 to flash the tire size from the 31.5" stock tires to the 34.5" KO2's.

 

[Novanotch]

I have a question, i think this is the best thread for it. Just installed a 3.5 lift with 37s on my Rubicon and it only gets to 6th gear now in the highway, I have to shift manually into 7th and 8th. What do I have to do in order to fix this? I heard re-gearing was not necessary.

 

[GARRIGA]

I have a question, i think this is the best thread for it. Just installed a 3.5 lift with 37s on my Rubicon and it only gets to 6th gear now in the highway, I have to shift manually into 7th and 8th. What do I have to do in order to fix this? I heard re-gearing was not necessary.

Not all 37s are created equal. Heavier tires going to act differently so you may need new gears. I’m assuming you flashed and corrected your speedometer. These new transmissions are so complicated anything out of sync may cause issues.

 

[Novanotch]

Not all 37s are created equal. Heavier tires going to act differently so you may need new gears. I’m assuming you flashed and corrected your speedometer. These new transmissions are so complicated anything out of sync may cause issues.

That makes sense. I went with Coopers which are supposed to be on yhe lighter side. Havent flashed yet, my tazer will be here Thursday. Maybe thats the issue.

Thanks for the response

 

[millercreek]

That makes sense. I went with Coopers which are supposed to be on yhe lighter side. Havent flashed yet, my tazer will be here Thursday. Maybe thats the issue.

Thanks for the response

If you look at the thread below (For those going with 37s, are you regearing??) I had the same experience as you and I am running the same tire as you. Read my posts (#5,#8,#10,#27,#28,#31 and #33). I now have about 5000 miles since regearing. Power is still a touch weak but I have all 8 gears. If I hold the speed at or under 55 I consistently get 19 - 20 mpg or more. However as I go up in speed the mpg falls off considerably. If one goes to the expense of regearing it would be disappointing to go with any thing other than 4.88s. My Rubicon runs the way I hoped it would. Best of luck with your decision.

 

[deitrick1]

If you look at the thread below (For those going with 37s, are you regearing??) I had the same experience as you and I am running the same tire as you. Read my posts (#5,#8,#10,#27,#28,#31 and #33). I now have about 5000 miles since regearing. Power is still a touch weak but I have all 8 gears. If I hold the speed at or under 55 I consistently get 19 - 20 mpg or more. However as I go up in speed the mpg falls off considerably. If one goes to the expense of regearing it would be disappointing to go with any thing other than 4.88s. My Rubicon runs the way I hoped it would. Best of luck with your decision.

I'm now at 4.88, but with a 6-speed. Power/torque gain not as noticeable as with my 2014 JKUR, but still an improvement over stock.

 

[VINDALOU]

Anyone have a sport manual transmission with 3.45’s and 35’s? I have the dana 30 front and 44 rear. Not that it matters.

I’ll be going 35’s soon but not re-gearing until I buy a locker for the rear.

Wondering how it would be. The manual feels great and first is super low (transmission first gear ratio 5.13) Might be ok for awhile.

I have the same has you with 35s after doing 2000miles , find rarely using 5th and 6th gear ,even on highway , very low rpm's ,thinking of going to 4.56 ratio, to get better rpm range,but hard to find info ,on what parts I need

 

[Geronimo]

After a 1000 miles and 500 of which were in the Texas Hill country on 37s, I am convinced I will be going to 4.88s. Its not terrible just not where I want it for pulling a camper and heading into real mountains.

 

[DesertsJL]

After a 1000 miles and 500 of which were in the Texas Hill country on 37s, I am convinced I will be going to 4.88s. Its not terrible just not where I want it for pulling a camper and heading into real mountains.

Look into 5.13 or 5.38 gears instead. Given the cost you don’t want to go too short on the gears. Pick a comfortable highway speed in 8th speed and gear to that.

 

[vavaroutsos]

Who actually makes 4.88s or 5.13s for the new JLUR axles? Last I read, no one was making them yet. Any leads appreciated.

Dana/Spicer make them. They have a PDF on their website with all the part numbers.

 

[butcho]

Thanks. When I gear Dana axles....I always use Spicer parts....but I didn't realize these were now out. Much appreciated.

Link for the lazy

https://www.jlwranglerforums.com/forum/threads/dana-advantek-axle-brochure.8030/

 

[Geronimo]

Look into 5.13 or 5.38 gears instead. Given the cost you don’t want to go too short on the gears. Pick a comfortable highway speed in 8th speed and gear to that.

I have not seriously looked at the ratio charts but will prior to buying a gear set, 4.88s is just a starting point in my thought process. Too deep can be an issue when it comes to long distances as well. But your point is well taken and certainly would be a consideration when making that choice.

I've seen Honda Accords on Black Bear....granted, going down; not up....but still. Even on 37s with stock gears (and a 4:1 tcase low gear) you should have ZERO issues.

I know what you are saying but I like running allot of those trails / passes using the least amount of break possible. Getting the gearing ratio back to where it was at stock is where I would like it to be. Using low gears without having to actually be in 4 low 1st (which would certainly hold) some of the other gears will start to run away and require breaking. 4 low 3rd was one of my favorites in our 2015 rubi with 456s. If any of that made any sense. Also the up hill towing of a camp trailer on the highway.

 

[Bravo]

Rubi Unlimited 6sp... going to run 37’s with either 5.13 or 5.38’s

 

[JLCashBurn]

The best source of info are Jeep Engineers and lift shops. If you move to 35" tires, they recommend 4.56, if going to 37s at a minimum 4.88, but 5.13 is preferred. The stock gearing - even Rubicon- does NOT ( I repeat NOT) support 35s. If you do not re-gear, the speedo will be off and MPG will take a major hit unless you buy a programmer. Its all about wear and tear so if you plan to keep your Jeep and throw tires on that arent supported, then to do it right, re-gear. If you want to have a better shot at warranty coverage, do the Mopar lift and the Mopar gears (they are now available). More money, but OEM is always better IMO.

To test this theory, I have 35s and the stock 3.45 gears - programmed. My RPMs went higher at speed and my MPH took a 2MPG hit. I re-geared to 4.56 just recently and the MPG climbed, RPMs dropped and I can actually getting into the higher gears on the freeway now. That and my Driveshaft no longer is taking extra stress.

You can ask random people in forums (these are the people here who say, "yea just throw on big tires on stock gears...runs fine" - yikes) or ask experts who either do this for a living / take advice from ones that engineered the JL - I know who I pick.

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