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

Bent Rim
Robin Stover | Writer
Posted May 1, 2008
Photographers: Phil Howell

A Study In Wheel Safety

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.

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