The Rule of Thumb for wire rope to sheave ratio is 20:1.

• A. 10:1
• B. 20:1
• C. 15:1
• D. 25:1

Answer: (B)

The main idea is to prevent excessive bending of the wire rope as it passes over a sheave. The 20:1 rule of thumb recommends that the sheave diameter be at least 20 times the rope diameter to keep the bend radius gentle. When the rope bends too sharply, the strands experience high bending stress, which accelerates wear, causes kinking, and leads to fatigue cracks. Using a sheave that is 20 times the rope diameter minimizes these stresses, extending rope life and improving safety. For example, a rope 1 inch in diameter should use a sheave at least 20 inches in diameter. Ratios smaller than this bend the rope too tightly and increase damage risk, while larger ratios are simply more forgiving but not necessary to meet the standard guideline.