Lug Nut Tightness Reliability: Application of Torque-Angle Signature Analysis for Installation / Auditing Studies

Reliable wheel attachment must start with proper tightening of the lug nuts in order to achieve the clamping force necessary to hold the vehicle's wheels securely for all operating conditions.

It is the purpose of this paper to provide a complete overview of the theory and practice of using torque-angle signature analysis methods to examine the installation and audits of wheel lug nuts. An accurate estimate of clamp load can be determined without actually measuring the clamp load.

The torque-angle signature analysis, known as “M-Alpha”, performed on tightening and loosening curves provides a powerful tool to understand the integrity of a bolted joint when clamp load data is not available. This analysis technique gives insight into the frictional effects, material properties, and geometric factors that can affect the clamp load attained during the installation process.