D:d Ratio

Notes & Use

Calculates:

  • D:d ratios for given pulley and cable sizes
  • Adjusted capacity of wire rope due to D:d bend
    • Note: that at a D:d ratio of 10 and less, permanent distortions of the rope will occur. (This is a general rule of thumb, different construction ropes will vary.)

Figure

Terms

$D_{tread}$ = Tread diameter, inches

$D_{cable}$ = Cable diameter, inches

Equations

Pitch Diameter, inches: $$ D_{pitch} = D_{tread} + D_{cable}$$

D:d ratio, unitless: $$ D:d = \frac {D_{pitch}} {D_{cable}} $$

Calculate the adjusted tensile strength of wire rope, percentage:

$$ F_{T-adjusted} = 1 - \frac {0.5}{\sqrt{D:d}} $$

Sources

Wire Rope. Mazzella Lifting Technologies, pp. 133-134.

Steel Rope Technical Information. Bridon International Ltd, pp 34.