These latches need to be replaced.
The stock four banger in the base model YJ offers good reliability but lacks power. Gearing helps for off-road adventures.
The stock skid plates on the YJ are sheet metal. The skid plates offer some protection for moderate off-roading.
The Stock YJ uses a twin master cylinder with a power booster. Manual transmission versions use a hydraulic clutch.
CHAPTER 2
TIRES AND WHEELS
Tires play a critical role for off-road performance. Striking a compromise between good highway handling and traction in all four-wheeling conditions is tricky. Choosing tires has become trickier for stock YJ replacements, as the market has changed and the choices are limited in the smaller sizes. But if you go more extreme, there are many choices, such as the Nexen Roadian MTX mud-terrain tire mounted on Raceline Monster beadlock wheels.
In 1987, the Wrangler YJ was introduced with 29-inch-diameter tires. At that time, 31-inch-diameter tires were large. When the YJ Renegade went on sale, it used 30-inch-diameter tires. Today, with moderate lifts, 35-inch tires are common on YJ builds. To run even a 31-inch-diameter tire requires about a 2.5-inch lift. Going up to 33-inch tires takes a 4-inch lift, and 35-inch tires require a 5-inch-plus lift. Tire diameters up to 40 inches are possible but require more clearance. We will explore lifts in the suspension chapter.
Mud-terrain tires, such as the Falken WildPeak mud-terrain tire (left), are generally preferred for serious off-road Wranglers. They are especially good on soft surfaces where the large tread blocks and softer rubber compound increase grip. They also look more aggressive. All-terrain tires, such as the BFGoodrich All-Terrain T/A tire (middle), appeal to more casual off-road use due to better wear and a quieter ride on the highway. While the AT tire may have a harder rubber compound, the increased tread area due to a smaller void ratio allows most all-terrain tires to perform with the equivalent mud-terrain tire in most off-road conditions. The Mickey Thompson Baja ATZ P3 (right) all-terrain tire blurs the line between mud- and all-terrain tires. More of a hybrid, the ATZ P3 features large tread blocks, a smaller void ratio, numerous sipes in the tread blocks, and a rubber compound softer than a typical all-terrain tire but harder than a mud-terrain tire. Many tires companies have introduced this style of hybrid all-terrain tire. This new category is often called extreme all-terrain.
Stock Replacement Tires
The stock wheels and tires on the Wrangler YJ are very small by today’s standards. The 15-inch, 6.5-inch-wide wheels allow few off-road tire choices. The 16-inch-diameter wheels offer more choices, but a maximum width of 7 inches restricts the selection. The 7-inch-wide rim of the stock YJ can handle up to about a 30-inch-tall tire on the stock setup for light-duty off-road driving. An increase in tire diameter requires a lift and more suitable wheels for the application.
Off-Road Tires
Most Wrangler YJ owners either purchase a used modified rig or plan to modify the Wrangler for capable off-road experiences. Larger tires are the current norm; 33-inch-diameter tires are on the small end of the spectrum. To use 33-inch-tall tires requires at least a 4-inch lift, while a 35-inch tire will need more than 5 inches of lift. Many YJs run 37-inch tires, and more extreme builds use up to 40-inch tires. Both require extensive modifications, usually a stretched wheelbase and the use of coilover springs and shocks.
Tires are the most-common performance modification to Jeep Wranglers. All-terrain and mud-terrain tires offer more aggressive looks and much-improved performance when you wheel off-road. But there is a downside.
All- and mud-terrain tires use a softer rubber compound, even softer on the mud terrains. This accelerates tire wear and increases rolling resistance due to softer tread compounds, so fuel economy takes a hit. The more aggressive tread designs of all- and mud-terrain tires increases road noise. This is most notable on mud-terrain tires. The larger tread blocks on a mud tire also increase tire squirm on the highway, which reduces handling responsiveness.
To have a good selection of off-road tires requires an upgrade to a larger, wider wheel. Taller tires will require a suspension lift for clearance. This improves off-road performance drastically. And the more-aggressive look of the all-terrain and especially the mud-terrain tires are an integral element of the Jeep persona.
All-Terrain Versus Mud-Terrain Tires
Which is better, an all-terrain or a mud-terrain tire? Which side of the fence are you on? While there has never been a clear winner in this argument, there are many factors to take into account: highway versus off-road miles, weather conditions, terrain, and road surface are just a few. But with the launch of a new off-road tire category, called by some the rugged terrain (RT) or extreme all-terrain, the line between all-terrain and mud-terrain is blurred. These new-generation all-terrain or RT tires offer more aggressive tread patterns and sidewalls while retaining a smaller void ratio for reduced noise on the highway and harder rubber compounds for better tire wear.
Tread Design Differences
The most obvious difference between the all-terrain and mud-terrain tire lies in the tread design. A mud-terrain tire has more aggressive tread blocks and a larger void ratio. The void ratio is the percentage of the total tread block area versus the area of the total tire tread. The tread blocks on a mud-terrain tend to be larger and thicker than an all-terrain tire.
The thin slits in the tread, called sipes, allow the tread to flex and the edges to better grip hard surfaces such as rocks. Sipes are used in both all-terrain and mud-terrain tires. Generally, an all-terrain tire will have more sipes, which improves grip on hard surfaces. The new, more-aggressive all-terrain tires create as much or possibly slightly more grip than the same size mud-terrain tire.
While a good mud-terrain tread design can keep rocks from lodging between tread blocks, the design must also eject mud and snow. Some designs do this more efficiently than others. In general, the larger void ratio of the mud-terrain is better in soft surface conditions, but the tread blocks need to flex to eject snow and dense mud.
Tread design plays a role but so does tire pressure. Lower tire pressure helps when the voids become filled with debris, ice, snow, or heavy mud. And some all-terrain tread designs are better in snow but lack the ability to keep small stones out of the tread voids.
Sidewall Design
One of the most important elements of tire design is the structure of the sidewall. When four-wheeling on rocks, in ruts, or on side slopes, it can be critical for the sidewall tread to have good grip. A lack of grip means the tire can slide sideways off the edge of a rock, the slope on a side hill, or within a series of ruts. Slipping can alter your desired path or cause you to bang a rock slider, skid plate, or bumper on a rock that you thought you could avoid.
The tire sidewall needs to be able to flex to conform to the road surface and to have a design that allows rocks and snow to be ejected from the tread pattern.
