Repeated bending and straightening of wire rope causes a cyclic change of stress called “fatiguing.” Bend radius affects wire rope fatigue life. A comparison of the relative effect of sheave diameter on wire rope fatigue life can be determined as shown below:

Ratio B	Relative Fatigue Bending Life
30	10.0
25	6.6
20	3.8
18	2.9
16	2.1
14	1.5
12	1.1

Example:
To determine the extension of fatigue life for a 3/4” wire rope using a 22.5” diameter sheave versus a 12” diameter sheave:

The relative fatigue bending life for a ratio B of 16 is 2.1 (see above Table) and ratio B of 30 is 10.

Therefore, we expect extension of fatigue life using a 22.5” diameter sheave to be 4.7 times greater than that of a 12” diameter sheave.