Wheels come off when the wheel nuts holding the wheel to the vehicle lose clamp force and become loose. There can be a number of reasons why a wheel nut can become loose.

• Over torqueing. Often users will over torque a wheel nut with the reasoning that tighter is better. However over torqueing actually stretches the studs or threads beyond their ability to respond. It can also result in cracked, seized or cross-threaded nuts and cracked wheels
• Under torqueing
• Joint settling after initial tightening and failure to re-torque
• Inadequate vehicle maintenance
• Thermal contractions This occurs when the nuts are mounted at shop temperature in a cold environment. As the nuts and bolt cools, clamping force is lost
• Improper mateing surfaces. This is referring to non-flat mating surfaces, damaged or bent hubs and wheels, or worn or elongated bolt holes
• Poor bolt and stud quality
• Contaminants
• Dirt, sand, rust, metal burrs, and paint on mating surfaces when present on the threads or between a nut and the wheel surface can create “false torques”. Where the force is used to overcome friction and is not converted to clamping force
• Excessive braking. Excessive braking can result in high temperatures (especially among heavy vehicles) causing the wheel bolts to expand and contract as the temperatures vary. This causes the wheel nut to lose its’ grip on the bolt, resulting in a loss of torque
• Age. Over time wheel nuts and bolts degrade and the clamp force diminishes to a point where it is possibly insufficient to secure the wheel adequately