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4x4 Wheel Failure Issues - Cause & Effect: Wheel Failures

Posted in How To: Wheels Tires on May 1, 2008
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Photographers: Phil Howell

Often overlooked but of utmost importance to vehicle safety are wheels. We see it time and time again-enthusiasts who assume rims are "all-good" as long as they hold air and don't leave the vehicle while driving. Such inattention to the little things that contribute to wheel safety is like leaving a loaded shotgun dangling from each wheelwell. Treated as such, and when ignored between outings, you're basically risking the lives of everyone on the road. After all, DOT wheel standards may seem strict initially, but in reality they simply cannot take into account every possible scenario, especially those of which are caused by trail abuse. Believing otherwise is simply ignorant. Sure, you might never experience a wheel failure, but trust us-they do happen. The National Highway Transportation Safety Administration said that 15 percent of all reported wheel-related automotive mishaps resulted in injury or death in 2005. For this reason, we thought it might be a good idea to expose a few of the issues associated with wheels and their use on 4x4s.

Cause: Extreme Force.
This cast-aluminum KMC racing wheel was involved in a spectacular multi-rollover crash during a CORR race qualifying round.
Effect: Favored by racers, this wheel is about as tough as a cast wheel gets. Despite its tremendous strength, it was totally destroyed by the lateral forces of the crash. This is an extreme case where something had to fail. We doubt any type of wheel would have survived this particular crash unscathed. However, a forged-aluminum or steel wheel would have likely stayed together rather than breaking apart.

Cause: Impact.
This forged-aluminum Center Line wheel survived a significant impact with a rock in Death Valley at high speed. The driver of the Dodge Ram diesel it was securely attached to assumed all responsibility for the mishap.
Effect: Forged wheels bend rather than shattering or cracking upon impact. Their strength, however, usually transmits abrupt and destructive forces to other parts of a drivetrain such as axles and knuckles.

Cause: Improper torque.
Many drivers are not aware that improperly torqued wheel nuts are a primary cause of misalignment or wheel failure.
Effect: Detachment.
This wheel came off the back axle of a toy hauler while cruising along at 55 mph. Luckily, nobody was killed when loose lug nuts allowed this wheel and tire to detach from the axle, crossing directly in the path of oncoming traffic. The way to avoid this scenario? It's imperative to adopt the habit of checking lug nuts whenever refueling. It takes less than five minutes, and may save a life and your financial future.

Cause: Impact.
This OE cast-aluminum Dodge Ram wheel suffered a hard hit on the backroads of Baja.
Effect: Hairline crack.
While it seems to hold air just fine, the right thing to do in this situation is replace the wheel with a whole new rim. A small hairline crack like this can end up causing the wheel to shatter at a later point. Take responsibility when your wheels get damaged; don't leave safety to chance.

The proper method of tightening lug nuts is another area where we see confusion. This diagram shows the proper way to tighten lug nuts on popular wheel types.

The topic of lug nuts always seems to surface when we talk with others about wheel safety. It is critical that the lug nut matches the thread diameter, pitch, and seat required by the wheels and studs. Otherwise, you're asking for problems. The three basic types of lug nuts are: conical seat (60 degrees taper "acorn" and "bulge"), the mag or shank style, and spherical or ball seat. Thread diameter refers to the diameter of the stud, measured across the shank at the outer edges of the threads. Thread-pitch means either the number of threads per inch or, if metric, the distance in millimeters between threads. The seat means the area on the wheel where the lug nut will clamp down.

Never attempt to use a lug nut that does not match the specific requirements of the wheel. Though they may look similar to other types, lug nut specifications are very specific and lug nuts should not be confused or installed incorrectly. Improper use almost always results in wheel damage and/or loss.

Rockcrawling and wheel damage go hand in hand. Professional rockcrawlers know this. That's why so many competition rigs have protective bead locks like the ones shown here. With this arrangement, very little damage can result from direct wheel-to-rock impact. A super-thick outer bead-lock ring protects the recessed bolt heads and prevents anything from reaching the face of the wheel.

Cause: Improper bolts.
This bead-lock wheel was the type where an off-the-shelf wheel is modified to accept a bead lock. While many enthusiasts run this type of wheel, we don't recommend it. Our reasoning lies in the long list of variables that the end user must deal with to ensure safe operation.
Effect: Injury.
As you can see, this wheel broke apart. The story goes like this: Our good friend (and Editor of 4-Wheel Drive & Sport Utility) Phillip Howell was assembling the outer "lock" ring to the bead receiver ring. As Howell sandwiched the tire bead between the two rings, he inadvertently failed to notice that each of the Grade-8 bolts was too long for the arrangement. Subsequently, as each bolt was tightened, the ones near the spokes bottomed out, acting like little jack screws. When Howell finished torquing the bolts, he made another mistake by filling the tire with a short hand-style air chuck instead of a longer safety lead. Together, with 30 psi inside the tire and the stress caused by the jack screws, the welds securing the bead-lock receiver ring to the wheel simply couldn't handle the pressure and failed. The results left Howell hospitalized with a cracked kneecap, broken fingers, and both hands swollen to the size of softballs.

The most common cause of tire failure is improper inflation pressure. Different wheels require different types of valve stems. Using the improper valve stem can result in slow leaks which, when unchecked, compromise safety and wheel function. The one shown here is the metal type that requires a rubber grommet to be sandwiched between a flange and a hex nut. Over the course of time, the hex nuts can loosen up and/or the grommet can flatten, causing slow leaks. Everybody knows it's important to check air pressure periodically, but many fail to realize the importance of replacing valve stems every time you replace your tires.

This picture shows the traditional type of rubber valve stems found on most wheels. Notice that one is larger than the other one. The two sizes are not interchangeable. One common issue we've seen with this type of valve stem relates to the internal valve core. Sometimes people forget to secure the cap after adding air or airing down. In this scenario, we've seen the valve core actually unthread itself and cause a flat tire while the vehicle is in motion. This can be avoided by simply replacing the cap after servicing the tire. Locking caps are also available to alleviate this problem.

Some of you may have stumbled into one of these little guys on a newer light pickup or SUV. What they are is a pressure-sensitive transmitter developed as part of the federal Transportation Recall Enhancement, Accountability and Documentations Act (TREAD). It was passed back in 2000 in response to a major recall of defective tires. These little sensors alert drivers when tire pressure drops below 25 percent of the manufacturer's recommended inflation pressure. The system is mandatory for all new vehicles with GVW ratings under 10,000 pounds, sold in the United States, beginning with the 2006 model year. On the upside, these little buggers are saving lives; as a drawback, they are rather delicate and feature temperamental seals that can easily be damaged during regular tire servicing. Unfortunately, they aren't cheap to replace, either, so if your rig has them, use caution whenever working around them.

Someday we may see a total shift in the way tires and wheels are manufactured. This photo shows the Tweel by Michelin. Essentially, it's an airless, integrated tire-and-wheel combination designed to take the pneumatic variable out of the equation. Instead of air pressure, the Tweel uses a series of energy-absorbing polyurethane spokes to dampen surface imperfections. It's believed that the first applications for this new technology will likely be used by military, where flat-proof tires would be a huge advantage to troops. At this time, we can only assume that the Tweel will eventually trickle down to everything from trail rigs to toy haulers. However, exactly when is unknown.

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