Winch Capacity

An internally driven winch has different characteristics than an externally driven winch. Externally driven winches aren’t that popular in the Towing and Recovery Industry anymore, but we often saw them on the old Helen 750’s. You would see a small gear that drives a large gear that’s visible on the outside of the winch drum. 

In today’s hydraulic planetary or worm gear style winches, the winching capacity or the pulling power of the winch is going to change depending upon how many layers of wire rope are laid on to the winch. A similar principle exists when you move the chain on the sprocket of a 10-speed bike. The smaller the sprocket the easier it is to pedal, the larger the sprocket the harder it is to pedal. 

When we look at your typical 8,000 lb capacity wire rope gathering winch, you will see that on a bare drum, or no wire rope on the winch, it has a pulling power of up to 8,000 lbs. As we increase the number of layers of wire rope on the winch it’s pulling power is reduced, because the diameter of the winch drum has increased, (just like you see on that 10 speed bike). After you install one layer of wire rope on the winch and you get to it later, theoretically the pulling power is reduced to 6,700 lbs. When moving to the next later, adding a third layer by wire rope to the winch, the pulling power is reduced down to 5,700 lbs. At the fourth layer 5,000 lbs. With 6 layers of wire rope on the winch, the pulling capacity of which is 4,500 lbs.

If this winch  were equipped with 3/8 fiber core wire rope we would have imposed a working load limit of 3,350 lbs on that wire rope. What an operator should see is that even after the pulling power of the winch has been reduced at 6 layers all the way down to 4,500 lbs, the winch still has the capacity to pull more than the wire rope we’ve assigned for the working load limit. 

Even after the pulling capacity of the winch has been reduced to 4,500 lbs at five layers of wire rope gathered to the winch, you can see that the working load limit can still be exceeded of the wire rope. A wire rope having a working load limit of 3,350 lbs can be exceed,  even at the fifth layer of wire gathered on to the winch. It’s important that every operator understands that the pulling power of the winch can exceed the working load limit of the wire rope. Therefore, when asked the question, “how much force should ever be placed on to my winch”, the answer is equal to the wire rope Working Load Limit.