Jeep JK FAQs

In the years since the advent of the Jeep Wrangler JK in 2007, scores of new enthusiasts have entered the Jeeping ranks. For many, the JK is their first Jeep, and they come loaded with questions. Here are some common questions I’ve asked myself at one point, or have seen others ask on the many Internet Jeep communities. Scroll through the list below, or use CTRL-F to search by keyword.

Suspension & lifts

Q: What components are necessary to lift my Jeep?

A: This varies slightly, based on your vehicle and the amount of lift you wish to achieve. This list, then, is a guideline for basic 2.5- to three-inch lifts for 2007 – 2011 JKs. (Model years 2012 to present will also require exhaust spacers.) To properly lift your Jeep, you should include, at a minimum, coil springs or spacers, bump stop extensions, longer shocks or shock adapters, longer brake lines or extension brackets, longer rear sway bar links (factory links or disconnects can be installed up front), an adjustable front track bar, rear track bar relocation bracket and some method – either drop brackets or control arms – to adjust caster and pinion angle. Two-door JKs like Smokey also will likely require a new front drive shaft.

Q: What are coil spacers?

A: Coil spacers are round pucks, most often polyurethane or steel, which sit above your Jeep’s coil springs. Smaller spacers are typically used to level sagging caused from the installation of armor or other heavy off-road equipment, while taller spacers are often used as an inexpensive way to achieve extra ground clearance.

Q: How can I level out my Jeep’s nose-down factory rake?

A: A leveling kit of three-quarters to one inch will raise the Jeep’s front end to eliminate the rake.

Q: Is there any reason, besides cost, to choose a coil spring lift over spring spacers?

A: Spring spacer lifts, commonly called “budget boosts” refer to the most basic lift, which raises the Jeep by installing polyurethane or steel coil spacers atop the Jeep’s factory coil springs. (For the Jeep JK, these are usually smaller lifts of about two inches in height.) While these kits are inexpensive compared to more fully featured suspension systems, they provide only extra ground clearance, but no additional active suspension or compensation for the added weight of armor and equipment.

Q: What are sway bar link disconnects, and why do I need them?

A: Sway bar link quick disconnects, or “discos”, are aftermarket front sway bar links designed to ease the process of disconnecting and reconnecting your front sway bar links for off-road use. Disconnecting your Jeep’s front sway bar links allows your front axle to more fully articulate when off-road. Allowing greater flex keeps all four tires on the ground as much as possible, providing greater stability and traction even in very uneven terrain.

Q: If disconnecting is good for the front axle, shouldn’t I also disconnect my rear sway bar links?

A: No. The soft construction of your rear sway bar’s torsion bar makes this unnecessary for all but the most hardcore wheelers. Longer rear sway bar links are, however, a commonly addressed component when lifting a Jeep JK.

Q: What is caster?

A: “Caster” refers to the angle of your Jeep’s front axle. Positive caster angles the Jeep’s pinion shaft slightly towards the ground. A Jeep with negative caster may experience “flighty” or wander on the road. All JKs leave Toledo with approximately 4.2° of positive caster; installing a lift and larger tires changes this angle, resulting in less-than-ideal driving characteristics. The use of control arm drop brackets or aftermarket/adjustable control arms reset this angle to at or near factory settings.

Q: What is an adjustable track bar, and do I need one?

A: After installing a lift, your axles will shift. The front axle moves left, while the rear axle moves right. Adjustable track bars re-center the axles.

Q: My lift didn’t come with bump stop extensions. Do I really need them?

A: Absolutely! Bump stop extensions prevent you from over-compressing your coil springs or bottoming out your shocks, either of which can cause permanent damage. Properly sized bump stops also prevent your tires from rubbing the fender flares at a full stuff. A good rule of thumb is to extend your bump stops approximately the same height as your lift. Some suspension system manufacturers offer adjustable bump stops, which allow you to fine tune your wheel up-travel.

Q: How much lift do I need to fit 33-inch tires?

A: The Jeep Wrangler JK (2007 – present) have enough room with factory fender flares to run most 33-inch tires on the road. With factory wheels, you’ll likely only see minor control-arm rubbing. To eliminate all chances of rubbing, or for those who properly wheel their Jeeps, it’s best to upgrade to wheels with 4.5 inches or less backspacing and/or add a leveling kit. These kits raise the Jeep’s front end three-quarters to a full inch, and can be found for about $150, depending on the brand. (Smokey’s Teraflex leveling kit includes front sway bar disconnects, and retails for $131.)

Q: How much lift do I need to fit 35-inch tires?

A: Assuming factory fender flares, a 2.5-inch budget boost or coil spring lift is the minimum required to clearance a 35-inch tire. To allow full wheel articulation with no rubbing, 3.5 inches is preferable.

Wheels & tires

Q: What is the largest tire I can run on my stock Jeep JK?

A: The largest factory size is a 255/75R17, which is about 32 inches in diameter and 10.5 inches wide. Some have run narrow 33-inch tires with little or no rubbing. Remember that questions of tire diameter, width and wheel size must all be considered to ensure a proper fit that doesn’t rub the frame or suspension components. As always, it is best to reprogram the Jeep’s onboard computer to ensure an accurate speedometer/odometer reading.

Q: I just bought new tires, but now my ride is terribly rough? Is there something wrong with my tires?

A: No. If you had the tires professionally installed, it is likely they have been inflated to too high a pressure for your use. Jeeps are much lighter than the trucks and sport-utility vehicles for which your tires were designed. To maximize comfort and prolong the life of your tires, it is best to reduce your tire pressure to between 26 and 30 psi. Reduce the air pressure in small increments, testing for ride changes, and perform a chalk test to ensure the proper ride and tire contact pattern.

Q: I was told to air down on the trail. How much pressure should I run off-road?

A: You’ll hear many opinions expressed within the Jeeping community. As a general rule, I recommend 15 to 18 psi on non-beadlock rims.

Q: Do my 35-inch tires really measure 35 inches?

A: Almost certainly not. No tire’s measurement, even without the Jeep’s weight on it, equals the value listed on the sidewall. Most fall about an inch below the listed size. For example, my 33-inch (metric equivalent) Goodyear Wrangler Duratracs measure 32.25 inches in diameter.

Q: What is the bolt pattern for a JK wheel?

A: The JK’s bolt pattern is 5-on-5.

Q: What size are the JK’s factory lugs nuts?

A: They are 1/2″-20RH, and can be removed with a ¾-inch or 19 mm socket. They should be installed to 95 ft.-lbs.

Q: What is backspacing?

A: Backspacing measures the distance from a wheel’s mounting surface to its inside edge, not to be confused with inset, which measures from the wheel’s outside edge to the outer surface.

Q: How much backspacing do I need on my wheels to run 12.5-inch wide tires?

A: As a rule of thumb, the consensus seems to hold that 4.5 inches of backspacing is the ideal figure for Jeep JKs. That said, a range of 3.75 to 4.75 inches might also be acceptable, depending on your specific tire choice. Toward the higher end, it’s possible you’ll experience some minor rubbing at full wheel lock. Conversely, at 3.75 inches, your tires will stick out very far, putting extra stress on your ball joints, axle Cs, etc.

Q: What are wheel spacers? Are they safe?

A: Wheel spacers (more properly called adapters) are aluminum rings, typically 1.25 to 1.5 inches thick, which are designed to be mounted in between your Jeep’s rotors and wheels. Installing wheel spacers effectively reduces the amount of back spacing your wheels have, allowing you to run wider tires on wheels with higher backspacing. It’s not uncommon to see spacers used on Jeeps running 12.5-inch-wide tires on factory wheels, which have 6.5 inches of backspacing. A 1.5-inch spacer effectively reduces this figure to five inches. Many view wheel adapters as unsafe, though the debate is hotly contested on both sides. It’s worth noting that many tire and wheel installers, such as Discount Tire, will not service a vehicle that employs wheel spacers.

Q: I’ve heard a lot of debate about larger tires being too big for my Jeep’s factory tire carrier. Who’s right, and what’s the risk?

A: As a unified system together with your Jeep’s tailgate, the factory tire carrier can support a load of up to 54 pounds. (A factory 32-inch BF Goodrich KM and Jeep 17-inch wheel weight a combined 49 pounds.) Placing a heavier wheel-tire combination puts added pressure on the spot welds in the tailgate’s sheet metal and over-stresses the factory hinges. I’ve personally seen a Jeep that suffered a cracked tailgate just from the added weight of a 33-inch tire. (The Jeep in question saw on-road use as a daily driver and modest off-road rock crawling.) Others have no problems with heavy 35s on the tailgate. Put simply, your Jeep is too costly an investment to risk. If you’re upgrading wheels and tires, plan on a tire carrier that transfers the load from the tailgate’s sheet metal to either the reinforced tub, a heavy-duty aftermarket bumper or the frame itself.

Bumpers & armor

Q: Will an aftermarket bumper interfere with my Jeep’s air bags?

A: No. The accelerometers that trigger the Jeeps’ air bags are not located in its bumpers. Installing an aftermarket bumper will IN NO WAY hinder your air bags’ deployment.

Q: What skid plates are standard on the Jeep JK?

A: Your Jeep JK Wrangler came with skid plates to protect the transmission, transfer case, gas tank and, on 2011 and newer models, the evaporation canister.

Q: OK, but how reliable are they?

A: Unless you are an extremely hard-core wheeler, the factory skid plates are functional enough to let you wheel all day and sleep well at night, with two caveats: The factory evap canister skid is very thin sheet metal, and the $100 investment in a proper skid plate is simply cheap insurance. Also, your oil pan does not have any factory protection. Investing in an oil-pan skid plate could make the difference between making it home from the trail, and spending a long night stranded in the middle of nowhere.

Drivetrain

Q: My owner’s manual says I have a part-time four-wheel drive system. What does that mean, and how is it different from the full-time 4WD on my Grand Cherokee?

A: Full-time four-wheel drive systems include a center differential to allow the front and rear driveshafts to turn at different speeds. It is safe to utilize these systems on dry pavement or normal driving conditions. The part-time system on the Jeep JK has no center differential, instead locking the front and rear driveshafts together. With a part-time system, rear-wheel drive should be used one dry pavement or surfaces with sufficient traction.

Q: How can I correct my speedometer for larger tires?

A: A number of companies manufacture programmers to recalibrate your speedometer for tires and gears, adjust your Jeep’s low-tire warning system, re-center the steering wheel for ESP and many other functions. Some, like the AEV ProCal I use, cost about $160, while other systems that offer more options, can cost several hundred.

Q: I need to re-gear for my new 35-inch tires. What’s the best ratio?

A: There are many opinions, and I don’t (yet) have any firsthand experience. The charts below, however, offer some good advice for returning your Jeep’s performance to stock. (Click to enlarge the images.)

Another tried-and-true method for determining the most efficient gear size for your vehicle is to use this simple equation:

Multiply your desired tire size by your Jeep’s factory gear ratio. Then, divide that figure by your original-equipment tire size. Round off the resulting figure to three digits, and match it to the closest available gear ratio. For example, I plan to run 35-inch tires on Smokey. The equation would look like this:

35 X 3.73 = 130.55

130.55/ 32 = 4.0796875 (Round up to 4.08)

A 4.08 is a near match to the factory-offered 4.10 gear ratio. But, of course, the performance of the 3.8-liter V-6 and my factory 3.73 gearing is sluggish at best. So, let’s plug in the lowest (highest numerically) factory ratio, the Rubicon model’s 4.10, into that equation.

35 X 4.10 = 143.5

143.5/ 32 = 4.484375 (Round off to 4.48)

The closest match to 4.48 would be 4.56, which is a popular gear choice for 35s. So, in our examples, we see that a 4.10 gear ratio would provide performance and fuel economy equivalent to my stock X-model gearing, while a 4.56 ratio would offer increased performance along the lines of what a stock Rubicon might normally see.

Q: Can I shift into four-wheel drive while my Jeep is moving and, if so, at what speed?

A: You can shift into 4WD high with the vehicle stationary or at speeds up to 55 miles per hour. To shift into low-range, you should be rolling about two or three mph. Shift your automatic transmission to neutral (or depress the clutch on manual transmission models), then shift the transfer case through the neutral position into low-range. Do not exceed 25 miles per hour while in low-range.

Miscellaneous

Q: My Jeep’s hard/soft top leaks when it rains. What can I do?

A: Sadly, this is a very common problem. And, not every Jeep JK leaks in the same location. Some owners have had luck adding weather-stripping. Jeep issued a troubleshooting PDF to its dealers, which may be downloaded here.

Q: My side-view mirrors leak for hours after I wash my Jeep. How can I stop this leak?

A: Drill a 1/8-inch or similar small hole in the plastic assembly below the mirror, where it mounts to the vehicle’s door. This will allow the water to evacuate more quickly down the side of the door. USE CAUTION when drilling, so you do not scratch the door underneath, creating a corrosion point.

Q: My Jeep leans to one side. Did something break?

A. Probably not. This is called the “JK Lean” and is caused by the positioning of the fuel tank, which runs longitudinal along the right side of the Jeep. You’ll likely notice the amount of lean varies from one day to another, as the amount of fuel in the tank — and, thus, the weight on that side — varies. A number of manufacturers offer spring spacers that can be used to compensate for the sag. Contrary to some early JK rumors, Jeep did not make special springs for use on the right side of the vehicle.

Q: What causes my factory half-doors’ air leak?

A. The design of the factory uppers and the pass-through design of their attachment point to the lower doors allows air to be channeled from outside your Jeep inside the factory door and into the passenger cabin at the door handle. Removing the lower door’s upper-door attachment sleeves and sealing the bottom will eliminate the air leak. NOTE: This remedy should not be used in areas that see a lot of rain or on vehicles that see daily driver use. The sealed channels may fill with water and overflow into the cabin.

Q: My factory speakers seem incredibly weak. Is there a way to improve their performance without replacing them?

A: You can see noticeable performance gains by removing the sound-bar speakers and filling the plastic cavity with poly-fill or other NON-FLAMMABLE stuffing material. Some have claimed a better bass sound can be achieve by drilling a small hole in the sound bar just above the rear speakers.

Q: How do I properly display the United States flag from my Jeep

A: Check out our post on proper vehicle flag etiquette here.

Q: How do I contact Chrysler if I have a problem which my dealer can’t (or won’t) resolve?

A: Fiat Chrysler maintains customer centers to handle exactly this type of situation. Make certain you have the following information handy when you call, or include it with any written correspondence: your name and address, telephone numbers where you may be reached, your dealership name, vehicle identification number, vehicle purchase date and mileage.

In the United States:
Chrysler LLC Customer Center
P.O. Box 21–8004
Auburn Hills, MI 48321–8004
Phone: (800) 992-1997

In Canada:
Chrysler Canada Inc. Customer Center
P.O. Box 1621
Windsor, Ontario N9A 4H6
Phone: (800) 465–2001

In Mexico:
Av. Prolongacion Paseo de la Reforma
1240 Sante Fe C.P. 05109
Mexico, D. F.
In Mexico City: 5081-7568
Outside Mexico City: 1-800-505-1300

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