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Wire Winch Lines- Part 1 & 2

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Wire winch lines are the heart of our recovery operations.  A damaged rope is a serious safety issue and a broken rope can remove a recovery vehicle from service.  Unfortunately, winch lines are often misunderstood.  In this post I will cover the basics of wire ropes and then follow-up with another post on how to select and what to look for during an inspection of your winch line.

  •       Cores: Serve as the foundation for the strands and keep the rope round and strands properly positioned.  There are 3 different core types.  Fiber Core commonly uses polypropylene fibers, but natural fiber ropes are available.  It has the greatest flexibility.  Independent Wire Rope Core (IWRC) have a wire rope as a core and has the greatest strength.  10-15% stronger than fiber core.  Strand Core uses strands of wires and is less flexible and mostly used on utility cables.
  •       Grades: The most common rope today is Extra Improved Plow Steel (EIP or XIP).  This is what is typically used on winch lines and is generally 15% stronger than Improved Plow Steel Grade (IPS).  Extra Extra Improved Plow Steel Grade (EEIP or XXIP) is also available for strength in higher rated equipment.
  •       Types: Bright wire is the most common and is un-coated.  Most winch lines use bright wire.  Galvanized wire improves the corrosion resistance, however, can reduce the strength by 10% compared to bright wire unless the wires are drawn again.  Stainless steel wire contains chromium and nickel.  It is very corrosion resistant and use primarily with yachts and control cables.
  •       Construction: Determines the trait of the wire rope.  For instance, a 6X19 will have 6 strands of rope that have between 19 to 26 wires per strand for better abrasion resistance.  A 6X37 construction has 27 to 49 wires and is more flexible while a 19x7 construction is rotation resistant.
  •       Lay: There are several types of lay.  Directional lay refers to the direction the strand face when looking down the rope- right or left.  Lay Orientation is either Regular or Lang.  Regular denotes how the wires are twisted in one direction while the strands are twisted in the opposite direction.  Lang Lay is the opposite of regular lay.  Regular lay ropes are less likely to untwist and less likely to fail because of crushing and distortion, however, they are less flexible than Lang Lay ropes.  Wire winch lines use regular lay construction.
  •      Design Factors: Are safety factors required by government and industry organizations for wire rope.  While they vary depending on application, typical towing winch lines have a 3:1 factor while lifting wire ropes have a 5:1 design factor.
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During a winch lines ‘useful life’ all wire rope will gradually lose strength due to surface wear and metal fatigue.  Metal fatigue is caused by normal use of the winch line but is made worse by excessive bending of the rope such as a sheave that is too small.  Inspecting your winch lines periodically for damage can save you many headaches on the road.  Below is mechanical damage to look for when inspecting your winch line.  All are grounds to remove the winch line from service.

  •          Hooks:  Any cracks or deformation.  If the throat opening has been enlarged by 15% or twisted out of plane by 10% or simply cracked.
  •          Broken Wires:  Pulling winch lines across edges, fatigue or overload can break individual wires.  If you find 5 or more broken wires in a single strand or 10 or more in one lay.
  •         Wear:  Dragging a winch line on the ground or loads over the line will cause flat areas on individual wires of the cable.  If these wires have lost 1/3 or more of the original diameter the line needs to be taken out of service.
  •          Corrosion/Heat Damage:  Any discoloration from rust or lack of lubrication promotes fatigue.  If the wire rope is severely pitted or individual wires rusted through replace the line.  Fiber core slings need to stay below 180° F and steel core below 400° F.  This amount of heat greatly reduces wire rope strength.
  •          Kinking:  Shock loading or forcing the line against an edge causes bent strands.  This prevents the rope from rotating properly and greatly reduces its strength.  Use load pads to protect the line.
  •          Crushing:  A load set on top of a winch line can flatten the cable.  This has the same effect as kinking and must be removed from service.

When selecting a new winch line it should be based on the diameter, length and type recommended by the winch manufacturer for the model of winch you own.

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