2017 Jeep JK Rubicon Recon

[Defiant Offroad]

Hi All,

I've had my Jeep "Defiant" for two years. The Jeep is a '17 Rubicon Recon Edition. I specifically sought out a Recon, because I wanted all the features of the Hard Rock (steel bumpers, LED lights) with the addition of the J8 front axle. The factory cast iron diff covers were an added bonus. I bought her at the end of July 2021. It's my third Jeep, but my first Wrangler (previous two Jeeps were both WJs). She was bone stock with 43k on the odo when I picked her up. As I've never really been much into extended vehicle travel, my goal from the get-go was to have a competent "trail rig" for day and weekend trips.
Three days after I got her:

Within two weeks of getting her back up here to VA (I purchased it in Jacksonville, FL), I outfitted it with an AEV 2.5" Dual-Sport Suspension (w/ control arm geometry correction brackets) and 33" General Grabber X3 tires, mounted on ProComp series 51 steel wheels. I ran this set up for the better part of a year and a half, and the Jeep performed nothing short of stellar everywhere that I took it. During this time, I also performed the "PUG" (Pentastar Upgrade), adding the newer style lower intake manifold and fuel injectors.
With the original off-road setup. Left pic from the Kentucky Adventure Tour, right pic from the George Washington National Forest:

This year, I've started to develop more of an interest in heading out for longer trips, so I've begun to overhaul the ol' girl a bit. She now has 123k miles (I drive the thing constantly), and a few months go I replaced the 33" Grabber X3s with another set of Grabber X3s in 35x12.50. Despite having factory LED headlights and foglights that actually work really well, I needed a bit more lighting when on the trails after dark. As such, I added Novsight's 3" LED driving light pods to the cowl area, and their 3" LED spotlight pods to the front bumper. I also added a Badland Apex 12000lb winch w/ synthetic rope. Given that nearly all of my trips are solo, the addition of the winch was way overdue and I freely admit that it should have been added at the beginning.
Here she is with the 35" Grabber X3s, Badland Winch, and Novsight lighting, again in the George Washington National Forest:


I'm preparing to take the plunge on an RTT, so last week I added a roof rack from Novsight, in preparation for receiving their RTT. I've also picked up an onboard freezer from SetPower, and I have a power station coming from Bluetti.
Here she is in her current configuration, awaiting the arrival of the RTT:


I have a few more things on the list to outfit her with, and I'll be sure to update as things are added!

Thanks!

 

[DintDobbs]

Nice set up. How does the gearing feel with the 35's? Think the weight of the RTT will affect it enough to consider a regear, or have you already regeared?

Those wheels look familiar.

 

[Defiant Offroad]

A regear is in the plans at some point in the next couple of months. She likes to downshift out of 5th on the highway if there's even the slightest incline.

 

[DintDobbs]

Do you happen to know what the axle ratio is at the moment? I wouldn't suggest lowering the gears by too much; I went from 29" to 33" tires and from 4.10 to 5.13 gears, and it made it almost intolerable to drive on highways. Roughly 12% increase in tire circumference, 20% difference in gear ratio, not smart for anything other than a dedicated off-roader.

Basically you want to keep three factors in mind: the percentage of size difference between the stock tires and the new tires, the weight difference between the stock tires and the new tires, and your target RPM's.

I would generally advise to gear as low as possible within your preferred range, specifically unless you need to use your truck on the highway. If you need to use your truck on the highway, absolutely keep the difference in gearing as close as possible to the difference in tire circumference. This will generally give the best trade-offs, with the only drawback being the extra weight of the oversized tires.

I don't assume this is your first rodeo with regearing, but if it is, my 2 cents might save you more than 2 cents.

 

[Defiant Offroad]

The current gears are the stock 3.73s. I'm going to regear to 4.10. I've run that combo before and it worked out fairly well.

 

[OTH Overland]

We have a 2013 10x Rubicon and it came stock w/ 4.10 gears, Installed a 3" lift and 35's. We do a lot of mountain passes, and the shifting of the trans totally sucked after the larger tires were installed. I am sure it would be worse with 3.73 slight grade would cause a downshift to 4th and then quickly to 3rd on any type of real incline. There is a huge gap between 3rd and 4th causing way to high of an RPM for my liking. Then it just would not want to upshift unless you took you foot all the way off the throttle. Ended up going with 4.88 gears and purchased a custom programed transmission control module that has the up and downshift ramp pressures modified. Still get a downshift to 3rd on mountain passes (We are very heavy) but it returns to 4th and 5th properly and is much more fun to drive. The manual shift function of the automatic now works properly too, could not manually force it back up a gear before. RPM is a bit higher at highway speeds, but seems to help push the weight along better. with 6,500 lb weight and a soft shell tent on the rack we are getting a 14mpg average vs a 19mpg average on long trips when it was stock. Also running a superchips flashpaq tuner to calibrate the speedometer and adjust some basic computer settings.

Combined with the 4:1 transfer case and new gears the Jeep crawls through obstacles amazing, but you do give up a lot of speed if using 4 low on a forest service road, trade off is worth it in my opinion.

 

[Defiant Offroad]

Finding that "sweet spot" for power v RPM is always a bit of an experiment!

We have a 2013 10x Rubicon and it came stock w/ 4.10 gears, Installed a 3" lift and 35's. We do a lot of mountain passes, and the shifting of the trans totally sucked after the larger tires were installed. I am sure it would be worse with 3.73 slight grade would cause a downshift to 4th and then quickly to 3rd on any type of real incline. There is a huge gap between 3rd and 4th causing way to high of an RPM for my liking. Then it just would not want to upshift unless you took you foot all the way off the throttle. Ended up going with 4.88 gears and purchased a custom programed transmission control module that has the up and downshift ramp pressures modified. Still get a downshift to 3rd on mountain passes (We are very heavy) but it returns to 4th and 5th properly and is much more fun to drive. The manual shift function of the automatic now works properly too, could not manually force it back up a gear before. RPM is a bit higher at highway speeds, but seems to help push the weight along better. with 6,500 lb weight and a soft shell tent on the rack we are getting a 14mpg average vs a 19mpg average on long trips when it was stock. Also running a superchips flashpaq tuner to calibrate the speedometer and adjust some basic computer settings.

Combined with the 4:1 transfer case and new gears the Jeep crawls through obstacles amazing, but you do give up a lot of speed if using 4 low on a forest service road, trade off is worth it in my opinion.

 

[DintDobbs]

I agree that 4.10 is too tall for 35's, but I also agree that 3.73 is too tall for stock. So, my 2 cents is probably worth zilch here.

Nevertheless, according to some basic math, 3.73 to 4.10 represents a roughly 9% change. 33" tires to 35" tires represents a roughly 6% change. This adds up to about a 3-4% change in final drive ratio.

So, post-4.10/35" swap, you're looking at a very slightly shorter gear ratio in the end result, with much heavier tires and potentially a heavy tent on the roof. Let's not even bother to calculate the expected weight of passengers, gear, pets, etc.

I strongly recommend using gears shorter than 4.10's in order to better handle all that extra weight. Nothing too ridiculous, may be 4.88's on the high end as suggested in this thread already. 4.10's are not ideal, based on the math and one other user's experience.

If you want the formula I use, it's this:

(A÷B)÷(C÷D) - 1

wherein

A = old gear ratio
B = old tire diameter
C = new gear ratio
D = new tire diameter

Subtracting 1 returns the % difference between old ratio and new ratio.

If the end result is <1, then you have a lower ratio than before. If your end result is >1, then you have a higher ratio than before.

There is no need to use tire circumference in this calculation; since that would require both multiplying and then dividing by π, its function is inherently negated.

 

[Defiant Offroad]

I appreciate the input.

I agree that 4.10 is too tall for 35's, but I also agree that 3.73 is too tall for stock. So, my 2 cents is probably worth zilch here.

Nevertheless, according to some basic math, 3.73 to 4.10 represents a roughly 9% change. 33" tires to 35" tires represents a roughly 6% change. This adds up to about a 3-4% change in final drive ratio.

So, post-4.10/35" swap, you're looking at a very slightly shorter gear ratio in the end result, with much heavier tires and potentially a heavy tent on the roof. Let's not even bother to calculate the expected weight of passengers, gear, pets, etc.

I strongly recommend using gears shorter than 4.10's in order to better handle all that extra weight. Nothing too ridiculous, may be 4.88's on the high end as suggested in this thread already. 4.10's are not ideal, based on the math and one other user's experience.

If you want the formula I use, it's this:

(A÷B)÷(C÷D) - 1

wherein

A = old gear ratio
B = old tire diameter
C = new gear ratio
D = new tire diameter

Subtracting 1 returns the % difference between old ratio and new ratio.

If the end result is <1, then you have a lower ratio than before. If your end result is >1, then you have a higher ratio than before.

There is no need to use tire circumference in this calculation; since that would require both multiplying and then dividing by π, its function is inherently negated.

 

[DintDobbs]

@Defiant Offroad I'm a math nerd with an unhealthy obsession with ratios, in case you didn't notice... A ratio of gear-ratio-to-tire ratios.

I've tested this formula by using my own truck and counting the RPM's where the speedometer reads 50 mph. In my case:

(4.10÷29) ÷ (5.13÷33) - 1 = .09

9% difference. This checks out, as my RPM's read 2000 at 50 MPH before, and now read right around 2250 (about 11% difference). Factor in the extra drivetrain friction from higher-speed rotation, weight of equipment and vehicle mods, extra tire weight, and extra road friction from wider tires, and that roughly accounts for the extra 2% difference in RPM's.

I would guess, without any absolute verification, that it gets about 10% worse fuel economy too. It wasn't amazingly good before, but now it's amazingly horrible! Consider this in your ultimate decision as well.

Let us know what you decide to do, and how it works out, and then spread it around for others who may decide to go that route!

 

[AggieOE]

4.10s with 34s (285/75/17) is what I'm running now and it's not bad but the mentioned downshift into 3rd at high revs is alarming especially when you have another few minutes to get up over the hill.
@OTH Overland , what exactly did you do to your transmission? Was a custom shop that did this or something common? I've also heard 4.56's are a good ratio for 35s to 37s. I'm currently debating if going to 35's is worth it. It's only another 1/2" taller but another 1" wider and ~10-lbs heavier. Mileage already sucks and to get anywhere out of Texas in a meaningful time, you have to do 80 to 85-mph for at least 12 hours.

 

[zgfiredude]

I too am at 4.10s and 34" tires........and live in Colorado, and pull a teardrop. Not happy with how it works. In all my math crunching, I "feel" like somewhere between 4.56 and 4.88 would be the place, which doesn't exist. And all the reading and advice I've looked at says "don't under do the change". So, 4.88 is likely the place.

 

[tjZ06]

The JK axles I put in my WJ were from a Recon (I searched for Recon axles for the thicker axle tubes and bigger Cs as well) and were 3.73s. Not a lot of ppl realize later-JK Rubicons (Recon or not) with the auto had 3.73s unless optioned to the 4.10s. Anyway, IMHO the cost of a regear isn't worth it to go from 3.73s to 4.10s. Yes, it's a 9% change but remember you're going to make the rig overall heavier (and a lot of that weight is rotating weight in the wheels/tires). Unless you expect to cruise at 80+ MPH regularly in your Overlander, I think you almost can't go "too deep" when you gear a rig. Especially since you have a JK with the 5spd auto, not the later JL 8spd with its 4.7:1 1st gear. I'd do at leat 4.56s, I went 4.88s for my WJ that runs a 35" and weighs ~5300lbs. With the 4.7 HO (265/335 HP/TQ) the 4.88s were great, definitely not "too much." I'm putting a 426cui GenIII Hemi in it, and I think the 4.88s will still be wonderful but obviously with the massive torque I could "get away" with a taller gear (but I won't be changing them).

-TJ

 

[Defiant Offroad]

I miss my old WJ! I loved the 4.7 H.O. motor.

The JK axles I put in my WJ were from a Recon (I searched for Recon axles for the thicker axle tubes and bigger Cs as well) and were 3.73s. Not a lot of ppl realize later-JK Rubicons (Recon or not) with the auto had 3.73s unless optioned to the 4.10s. Anyway, IMHO the cost of a regear isn't worth it to go from 3.73s to 4.10s. Yes, it's a 9% change but remember you're going to make the rig overall heavier (and a lot of that weight is rotating weight in the wheels/tires). Unless you expect to cruise at 80+ MPH regularly in your Overlander, I think you almost can't go "too deep" when you gear a rig. Especially since you have a JK with the 5spd auto, not the later JL 8spd with its 4.7:1 1st gear. I'd do at leat 4.56s, I went 4.88s for my WJ that runs a 35" and weighs ~5300lbs. With the 4.7 HO (265/335 HP/TQ) the 4.88s were great, definitely not "too much." I'm putting a 426cui GenIII Hemi in it, and I think the 4.88s will still be wonderful but obviously with the massive torque I could "get away" with a taller gear (but I won't be changing them).

-TJ

 

[MidOH]

4.88. Don't fear the gear.