What is a sign of looseness in lug nuts?

Rust trails are indeed a sign of looseness in lug nuts. When lug nuts are properly tightened, there should be no movement between the nut and the wheel. However, if the lug nuts are loose, the wheel can shift or vibrate during operation. This movement can create wear on the interface between the nut and the wheel, allowing moisture to seep in and form rust. Over time, these rust trails can become visible, indicating that the lug nuts are not securely fastened and may require immediate attention to ensure safety.

Other options do not reliably indicate looseness in lug nuts. Color variation and size changes in the lug nuts themselves typically do not correlate with their tightness; they may be influenced by materials or coatings. Temperature differences can occur for various reasons and are not a direct sign of lug nut tension. Focusing on rust trails as a clear indicator helps maintain vehicle safety by prompting timely inspections and necessary adjustments.