The top 13 first mod­i­fi­ca­tions we would make to the all-new 2018 Jeep Wran­gler

Four Wheeler - - Contents - By John Cappa editor@fourwheeler.com Pho­tos: John Cappa and cour­tesy of Jeep and Mopar

The top 13 first mod­i­fi­ca­tions we would make to the all-new 2018 Jeep Wran­gler

WHEN­EVER A NEW JEEP WRAN­GLER IS in­tro­duced, en­thu­si­asts and the af­ter­mar­ket rush to be the first to make mod­i­fi­ca­tions, and the all-new ’18 Jeep Wran­gler JL is no dif­fer­ent. The chal­lenge is iden­ti­fy­ing what should be im­proved upon and what can be left alone. The mod­i­fi­ca­tions needed for the out­go­ing Wran­gler model may not nec­es­sar­ily be what’s needed on the new Wran­gler. For ex­am­ple, the new JL Ru­bi­con is said to fit 35-inch tires stock, it has a mas­sive 1.58-inch–di­am­e­ter tie rod and draglink, and is avail­able with an op­tional off-road–wor­thy steel front bumper. Be­cause of the big­ger wheel open­ings, lift kit sizes for the JL will surely need to be dif­fer­ent than what’s avail­able for the JK. It seems as though many of the things on the JK that had to be ad­dressed by the af­ter­mar­ket have been ad­dressed from the fac­tory with the JL. With all this in mind, we de­cided to spend a week in the new Wran­gler JL and look at it with fresh eyes to come up with the top 13 mod­i­fi­ca­tions we would make first. We spent our on- and off-road wheel time in a Wran­gler Un­lim­ited Ru­bi­con model, which will likely be one of the more pop­u­lar trim lev­els for dirt-driv­ing en­thu­si­asts. How­ever, many of the mod­i­fi­ca­tions we have listed here will work on the other JL trim lev­els as well.

Rocker Guards

Pretty much ev­ery 4x4 that hits the dirt should have some type of rocker area pro­tec­tion. How ro­bust this body pro­tec­tion needs to be will de­pend on how you plan to use the ve­hi­cle, and the same is true with the new JL Wran­gler. The fac­tory Ru­bi­con rocker guards are fine for gen­eral off-road use and pro­tec­tion against park­ing lot door dings and ghost-rid­ing shop­ping carts. They at­tach at the body, so they re­ally are not de­signed to sup­port the weight of the en­tire Jeep when reg­u­larly slid­ing over boul­ders and rock ledges. If ag­gres­sive off-road­ing is in your plans, you’ll want to add rocker guards that in­cor­po­rate the body mounts or at­tach di­rectly to the frame. This will bet­ter pro­tect the alu­minum doors and steel rocker area of the JL.

No-lift Tire Size

The fac­tory JL Ru­bi­con tires are 285/70R17, which mea­sure out to around a 33-inch tire. With no lift, the man­u­fac­turer says that 35s will fit for street use, but with the sus­pen­sion fully ar­tic­u­lated off-road there will be some tire rub on the in­ner wheel­wells both front and rear. We think you could get away with bump­ing up the tire di­am­e­ter one to two sizes to a 305/70R17 or 305/75R17 on the stock wheels with only mi­nor in­ner fender con­tact at full sus­pen­sion ar­tic­u­la­tion. Of course, if you are will­ing to re­move the plas­tic in­ner wheel­wells and lower the bump­stops or live with sig­nif­i­cant tire rub off-road, you could surely fit a 35x12.50 or 315/70R17 on the stock Ru­bi­con wheels.

Fit­ting 35x12.50 or 37x12.50 Tires

With the gen­er­ous wheel open­ings, it seems nat­u­ral that the Ru­bi­con model should have 35-inch tires. In or­der to cleanly fit 35x12.50 or 315/70R17 tires both on- and off-road, a 2-inch lift kit could be im­ple­mented. How­ever, this seems to leave the wheel open­ings look­ing empty. We think a 1-inch lift or 1-inch bump­stop ex­ten­sions could be used to keep the tires out of the wheel­wells. You might be able to re­tain the fac­tory Ru­bi­con wheels, but you’ll likely want wheels with around 1-inch less backspac­ing. Fit­ting 37-inch tires will re­quire a 2-inch lift, bump­stop ex­ten­sions, wheels with less backspac­ing or wheel spac­ers, and prob­a­bly some in­ner fender trim­ming.

Ru­bi­con Flare Swap

The fac­tory high-line fender flares are part of the rea­son the 285/70R17 tires fit on the Ru­bi­con. Th­ese fac­tory flares in­crease the size of the wheel open­ing and could be bolted onto the non-ru­bi­con mod­els to pro­vide more tire clear­ance.

Cut-to-fit Flares

There will surely be those that want to step into taller and wider tire and wheel pack­ages with­out mod­i­fy­ing the sus­pen­sion. This looks like it could be done with­out much cut­ting. The fender flares are made from two pieces. You should be able to re­move the plas­tic riv­ets and take off the lower por­tion of the flares along with the marker lights on the front flares. This would pro­vide an ad­di­tional 2 inches of outer fender flare clear­ance. Of course, you’ll still have to ei­ther trim or re­move the in­ner fender lin­ers be­cause they will no longer have any sup­port along the outer edge.


If no tire size in­crease is planned, we’d have a re­ally hard time mess­ing with the JL sus­pen­sion given the smooth ride and great per­for­mance on- and off-road. How­ever, one area that could use some im­prove­ment in the dirt is the shocks. If you like wheel­ing around the desert at speed, you’ll quickly over­heat the fac­tory shocks. We’d like to see some bolt-on, lightly-valved, po­si­tion-sen­si­tive shocks be made avail­able for the JL. It shouldn’t be too tough; there is plenty of room and all four shocks now fea­ture heavy­duty eye mount­ing at both ends. We’re think­ing larger-di­am­e­ter ad­justable ex­ter­nal or in­ter­nal by­pass shocks would be a great ad­di­tion to an oth­er­wise stock JL sus­pen­sion sys­tem.


The fac­tory stamped steel skid­plates will pro­vide am­ple pro­tec­tion in most off-road sce­nar­ios; how­ever, reg­u­lar rock con­tact will take its toll on the light-duty OE fuel tank and trans­fer case skid­plates. If you fore­see gran­ite in the fu­ture of your JL’S un­der­side, the main struc­ture of the orig­i­nal trans­fer case/trans­mis­sion skid­plate will ben­e­fit from a heavy-duty re­place­ment. Real bash­ers will want a skid­plate that ex­tends for­ward to pro­tect the au­to­matic trans­mis­sion lines, ex­haust cross­over, and en­gine oil pan. We’d love to see some­one make use of UHMW ma­te­rial on the skid­plates to help the JL slide more eas­ily over ob­sta­cles. Also, even though the sus­pen­sion con­trol arm brack­ets on the front axle are tucked up rel­a­tively well, they would ben­e­fit from some weld-on skid­plate gus­sets.


The JL front and rear drive­shaft ar­chi­tec­ture is very sim­i­lar to the drive­shafts found un­der the JK. The rear drive­shaft fea­tures CVS on both ends and the front drive­shaft has a CV on the trans­fer case end and a U-joint on the axle end. In most cir­cum­stances, the CV joint is ac­tu­ally a bet­ter de­sign than a U-joint. How­ever, the Cv-style drive­shafts are far less tol­er­ant of joint bind and be­ing dragged over boul­ders. Taller lifts, in­creased wheel travel, and rocky wheel­ing will gen­er­ally be best ac­com­plished with front and rear af­ter­mar­ket drive­shafts with U-joints at both ends. The good news is that you no longer need to mod­ify the ex­haust for drive­shaft clear­ance when lift­ing the Wran­gler. The fac­tory JL ex­haust should clear the front drive­shaft fine with sev­eral inches of lift.

Axle Gear­ing

The new ZF 8HP eight-speed au­to­matic trans­mis­sion in the JL re­ally makes great use of the power avail­able from the 3.6L V-6, so much so that we think the Ru­bi­con 4.10:1 ra­tio axle gears should be good for up to 35-inch tires. Bump­ing up to 37-inch tires will likely re­quire 4.88:1 or 5.13:1 ra­tio axle gears, which are not yet avail­able at the time of this writ­ing. The jury is still out on what axle gears would be needed for the op­tional 2.0L four-cylin­der gas turbo en­gine and 3.0L diesel.

Speedometer Cor­rec­tion

As with all mod­ern 4x4s, the en­gine and au­to­matic trans­mis­sion per­for­mance is ex­tremely de­pen­dent on ve­hi­cle speed in­put. Al­ter­ing the tire di­am­e­ter and axle gear ra­tio will cause the in­put speed to be in­cor­rect, which can lead to much more than a false speedometer read­ing. Re­sults in­clude in­cor­rect trans­mis­sion shift points, poor shifts, and even trans­mis­sion over­heat­ing and fail­ure. The cure is sim­ple. Cor­rect the speedometer so the en­gine and trans­mis­sion com­put­ers re­ceive ac­cu­rate speed info. This can be done sev­eral ways, but it’s typ­i­cally done with an af­ter­mar­ket con­troller that plugs into the OBDII port. As of this writ­ing, there aren’t any prod­ucts avail­able to make the cor­rec­tion on the JL, but we are sure they will be avail­able soon.

The all-new Dana 44 axles found in the front and rear of the JL Ru­bi­con are said to have been en­gi­neered with up to 35-inch tires in mind. The mas­sive 2.75-inch front and 3.12-inch rear axle­tubes will cer­tainly pro­vide more beef un­der­neath. One area of dis­con­tent for many Jeep en­thu­si­asts is with the JL cen­ter axle dis­con­nect (CAD) sys­tem, and rightly so. The YJ CAD sys­tem left a bad taste in the mouth of Jeep­ers as far back as 30 years ago. How­ever, the prob­lem­atic YJ sys­tem was vac­uum op­er­ated. The JL uses an elec­tric so­le­noid, sim­i­lar to the front axle dis­con­nect found in cur­rent­model Ram 2500 and 3500 trucks as well as many other mod­ern 4x4s. The real ad­van­tage most peo­ple for­get is that the JL front drive­shaft and ringand-pin­ion will not be spin­ning when the trans­fer case is shifted into two-wheel drive. This will re­duce drivetrain wear and vi­bra­tion and in­crease fuel econ­omy. Also, spin­ning bent and un­bal­anced front drive­shafts in the out­go­ing JK have been known to cause the trans­fer case to split in half on the high­way. Re­gard­less of if the JL front axle dis­con­nect is a prob­lem, we’re sure the af­ter­mar­ket will of­fer CAD delete axle­hous­ings, axle­shafts, and other prod­ucts to keep every­one happy. Al­though, we would prob­a­bly save our money for a while to see if the JL CAD sys­tem ac­tu­ally be­comes prob­lem­atic.

On­board Air

The one thing we re­ally hoped the new JL Ru­bi­con would come with was a fac­tory air com­pres­sor that could be used to in­flate tires, air mat­tresses, and recre­ational floats. For­tu­nately, the af­ter­mar­ket is flush with many dif­fer­ent air com­pres­sors. Un­for­tu­nately, there isn’t a lot of space un­der the JL hood for ac­ces­sories. Even a dual bat­tery kit will be a tight fit. We’d like to see some­one make use of the re­mov­able plas­tic tray in the rear trunk area. The tray could be eas­ily re­placed with a steel or alu­minum block-off plate that houses an elec­tric air com­pres­sor and a small tank, which could be tapped into from the rear of the Jeep with a chucked air hose.

Ad­di­tional Light­ing

The op­tional LED light­ing group in­cludes LED head­lights which are sig­nif­i­cantly more use­ful at night than some of the head­lights used on past Jeep mod­els. This light­ing pack­age will set you back a cool $895. It helps night vi­son im­mensely, but still does lit­tle to re­ally reach out long dis­tances into the dark off-road. For light­ing up the im­me­di­ate area around the Jeep, con­sider some af­ter­mar­ket LED lights mounted to the front bumper or any­where you need to see. For high-speed wheel­ing or if you want to see way out into the night, look for some spot beam HID lights.

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