Tire Cutting, Slashing, and Ply Ratings
Cutting or puncturing a tire tread or slashing a sidewall is a fairly common occurrence off-road. Areas with sharp rocks are the most likely to cause problems. Two factors will help reduce the possibility of serious tire damage: running only load range D or E tires and airing down to a lower tire pressure.
Load range refers to the ply rating. Old bias-ply tires had a ply rating of up to 10 ply for light truck and off-road tires. With modern materials, fewer plys are needed to achieve the same strength and puncture resistance. A D rating is the equivalent of an 8-ply bias tire. An E rating is the equivalent of a 10-ply bias tire. Tires with D and E ratings provide the best protection off-road.
The BFGoodrich Mud-Terrain T/A KM2 is the latest in a long line of BFGoodrich mud-terrain tires. Every new version exceeds the capability of the last. This tire shines in the rocks and any soft surface. Tread wear and road noise are pretty typical of most mud-terrain tires.
The Maxxis Trepador Competition mud-terrain tire is very capable in extreme conditions. This tire is heavy and noisy on the highway but offers great performance in severe conditions and rock crawling situations. The tread and sidewall are very aggressive with deep tread blocks and a large void ratio.
The latest mud-terrain tire offering from Maxxis is the Razr. Featuring a new tread compound and tread block design, the Razr is designed to improve on-road performance and reduce noise while retaining great off-road traction and durability in all types of terrain.
For those with stock or slightly modified Wrangler YJs, the Maxxis Bighorn MT-762 is offered in several 15- and 16-inch-diameter wheel sizes as small as 29 inches tall.
The very aggressive Maxxis Creepy Crawler offers a high level of off-road traction in slippery conditions and in the big rocks while being DOT legal for highway use.
The Pro Comp Xtreme MT2 is another mud-terrain tire available in a wide range of sizes to accommodate mild to extreme YJ builds.
The Falken Wildpeak M/T features a stiff sidewall construction. This tire needs to be aired down more to achieve the same tire contact spread as a softer sidewall tire. At the top, the tire pressure is 28 psi and in the middle the pressure is about 12 psi, which is about the lowest advisable for non-beadlock wheels. The lower the tire is aired down (to 6 psi), the more effectively the tire conforms to the rock. This series of photos was taken on a much heavier Jeep. A lighter YJ would need even lower tire pressures for good contact patch compliance.
Tire Pressures for Jeep Wrangler YJ Off-Road
There are four important reasons to air down tires. First is to increase traction by increasing tire contact patch area. A 285 70-17 10-ply tire with inflation pressures reduced from 50 psi to 7 psi will increase the tire contact patch by up to 220 percent.
Second, aired down tires improve ride comfort. There is a significant difference.
Third is to reduce the chance of a sidewall puncture. Think of a highly inflated balloon. If you poke at it, it will likely puncture. A softly inflated balloon, when poked, has considerably more give and is not likely to puncture.
Fourth, aired down tires reduce damage to the road surface by spreading the weight over a greater tire contact patch surface area. This helps reduce erosion over time.
There are also some disadvantages, including reduced ground clearance due to a shorter sidewall from less pressure, increased possibility of the tire bead unseating from the wheel rim, and the need to air back to recommended highway tire pressures for your vehicle. For hard surfaces and rock crawling, higher pressures are needed to help keep the tire bead seated on the wheel rim and to protect the sidewall and tire bead from bottoming on the rim, which would likely damage the tire or even bend the wheel rim.
Airing down tires to a lower pressure allows the tire to conform to the terrain, increasing traction. This is very important for rock crawling for both climbing and descending. This tire is at about 15 psi and the tire contact patch and the sidewalls conform to the rock edge, allowing a much easier climb up the rock. With this Raceline Monster beadlock wheel, we have aired down as low as 4 psi on soft surfaces such as sand and snow.
Tire Deflator Types
Tire deflators are the easiest way to air down tires when you hit the trails. In general, there are three types of deflators.
The first type are tire pressure gauges that have a release valve for letting air out of a tire. These are very slow and require constant attention.
The second type are deflators that screw onto the valve stem and depress the spring-loaded valve core. These are adjustable for minimum pressure when they shut off. They usually come in sets of two or four. They are not much faster than a pressure gauge, but with four and automatic shut off, you can screw them on and walk away.
Wheelspin is always an issue when climbing steep rock ledges. The BFGoodrich Mud-Terrain T/A KM2 features a fairly stiff sidewall construction. Combined with the light weight of the YJ, this tire could have benefited from a lower tire pressure when airing down. The reduction in ground clearance from a lower tire pressure is not an issue, at least in this spot.
The Currie deflator removes the valve core from the valve stem, which allows rapid deflation. The gauge allows precise pressure monitoring. The deflator consists of a gauge, a plunger that unscrews the valve core, a fitting that screws onto the valve stem, and a pressure release valve. While the operator is a little more involved in the process, this is the fastest way to air down four tires—even faster than the set of four screw-on deflators. The cost is about half.
The valve core is spring loaded, so when the valve is depressed, air can flow in under pressure or out to air down. The airflow is very restricted by the valve core. The Currie deflator removes the core but captures it within the housing for easy replacement.
To use the Currie deflator, screw the fitting onto the valve stem, depress the plunger and rotate until it captures the valve core, unscrew the valve core, and pull the plunger out. Open the air valve to deflate, close the air valve to check pressure. When the desired pressure is reached, keep the valve closed, push in the plunger, and screw in the valve core until snug. Then, pull the plunger out so that the valve core cannot be unscrewed while unscrewing the fitting from the valve stem. Our project YJ weighs in at about 4,000 pounds. To get good tire contact patch spread on the fairly soft sidewall Nexen Roadian MTX tires, we aired down to about 6 psi. Beadlocks are a necessity at these low tire pressures.