How To Buy And Maintain Wire Rope For Your Tow Truck?

Wire rope is the lifeline of your tow truck. We’ll help you understand the terminology, construction and ratings of wire rope. We’ll also give you advice on what type of rope to buy, how to attach it to a hook without losing towing capacity, how to inspect and maintain it, how to prevent damage, and how to tell when it’s time to replace it. We’ll also give the pros and cons of synthetic versus wire rope.

IS WIRE ROPE THE SAME AS CABLE?

“Wire rope,” “line,” “rope” or “wire” are the only correct ways to refer to wire rope, but many tow operators refer to it as cable. Wire rope is not cable. Cable is only an acceptable term when referring to a piece of wire rope that is terminated on both ends. When that cable is connected to a power source, such as a winch, it’s no longer acceptable to call it cable.

WIRE ROPE CONSTRUCTION

The Egyptians were among the first to twist and braid strands of plant material together to form rope. Today’s rope is made of different materials and using different methods, but the basic principle remains the same: smaller diameter material is twisted to form strands, and then those strands are twisted to form the rope (or wire, if the rope is made from steel).

The pictures below show a 6 x 19 wire rope. The ‘19’ refers to the number of smaller diameter wires that are twisted together to form a single strand. The ‘6’ refers to the number of strands that are twisted together to make the wire. The middle of the rope, which isn’t included in either number, is referred to as “the core.”

6 x 19 wire rope end view6 x 19 wire rope side view 

LAYS OF WIRE ROPE

You might have seen the term “lay” when a manufacturer specifies the type of wire to be used on a piece of their equipment. Lay refers to the direction of the twist of the wires in a strand (right or left) and to the direction that the strands are laid in the rope (regular or lang).

When you inspect a rope with regular lay, the wires appear to run straight down the length of the rope. With lang lay, the wires twist in the same direction as the strands, giving the appearance that the wires run across the rope. Regular lay rope is the most common wire sold today.

HOW MUCH CAN YOUR WIRE ROPE HANDLE?

Just because your wire rope says it’s rated for an ultimate load (UL, or breaking strength) of 39,000 lbs doesn’t mean you can use that rope to tow 39,000 lbs. That’s because every wire rope has a working load limit (or WLL), which is the actual mass or force the product can support. It’s the working load limit you shouldn’t exceed, not the ultimate load limit.

So why don’t rope manufacturers make our lives easier by giving the WLL on their packaging instead of the UL? That’s because wire rope can handle different weights depending on how it’s being used. Different industries have different WLLs.

The working load limit for the towing and recovery industry is ¼ of the ultimate load.

To figure out the working load limit of any wire rope used in towing and recovery, use this formula:

ULTIMATE LOAD  /  4  =  WORKING LOAD LIMIT

For example, standard 1/2” 6 x 19 wire rope has an ultimate load of 26,600 lbs. The working load limit for towing and recovery is 26,600 divided by 4, which is 6,650 lbs.

These ratings must be adhered to for the safe operation of the equipment you are using. You’ll notice that most manufacturers are very liberal with their warning labels to minimize their liability.

HOW TO BUY WIRE ROPE?

When it comes to buying wire rope, there are a few things to consider.

Grade of steel. Wire rope is constructed with different grades of steel the same way that chain is manufactured. The most common wire rope grade is extra improved plow steel (EIPS) but you can also select extra extra improved plow steel (EEIPS) that is 10% stronger.

Steel core vs fiber core. When wire rope is constructed, the strands and wires are wrapped around a center core made of either independent wire rope core (IWRC) or fiber core (FC). IWRC, which is made of steel, provides additional strength. Fiber core cushions the strands by accepting lubricant more effectively. For the towing industry, we feel that the benefit of increasing our single line rating with steel core wire outweighs the benefits that fiber core offers.

Strength of rope. When it comes to wire rope, as with many things in life, you get what you pay for. A 1/2” standard 6 x 19 steel core wire rope has a working load limit of 6,650 lbs. If you go for a ½” Python COMPAC 6 steel core rope, your WLL increases to 7,550 (14% increase). Opt for a ½” Python COMPAC 35 steel core rope and your WLL increases to 9,100 (a 37% increase over then standard wire). The COMPAC 35 rope will cost you three times the price of the standard 6-strand wire, though.

Lang lay or regular lay. There are advantages and disadvantages to both lang and regular lay wire rope, depending on the application. Most manufacturers specify the types and lays of wire rope to be used on their piece of equipment. Be sure to consult the operator’s manual for proper application.

Quality of manufacturer. Talk to your wire rope supplier about the rope manufacturer. Imported wire rope is very common in today’s marketplace and many of these suppliers are quality manufacturers. The only way you can tell the quality is by asking questions about the product you’re buying.

PREVENTING DAMAGE TO WIRE ROPE

It’s important to regularly inspect your wire rope for damage. The most common signs of damage are broken strands, kinks, and flat spots from improper wrapping on the winch drum. Constantly inspect your wire during a recovery to ensure that the winch is gathering wire properly on the winch drum and the wire is properly layered on the winch. If you want to prolong the life of your rope, take the time to unwind and rewind your wire at the first sign of overlapping or bird nesting and always stay within the working load limit.