There are several types of winches on the market. For off-road vehicles in general, you'll find electric and hydraulic winches. Your vehicle's battery is the power source for an electric winch -- you just hook a couple of wires to the battery and you're ready to go. Hydraulic winches pull power by tapping into the hydraulic system of a power-steering pump. But with ATVs, you really only need to look at electric winches. Even so, not all electric winches are alike.
The winch's electric motor provides power to a set of gears called the gear train. There are two types of gear trains for electric winches: planetary and worm. A planetary gear train uses several gears to turn the winch's drum. It turns the drum quickly, which translates into a faster cable-pulling speed. It also creates heat. Worm gear trains only have two gears. They turn drums more slowly than planetary gear trains and don't generate as much heat. While worm gear trains may be slower than planetary gear trains, they also tend to be more powerful.
You can get an idea of how strong a particular winch is by looking at its rated line pull. This is the maximum amount of weight the winch manufacturer says the winch can pull safely. In the United States, this number is listed in pounds.
Another differentiator for winches is in the type of line they use. Some winches use steel cable and others use synthetic rope. A few winches can accommodate either type of line. Synthetic rope is strong and is less dangerous in the event of a line break than cable; however, synthetic rope can wear faster than cable and can also melt if near a heat source for a long time -- such as a winch using a planetary gear train. Cable won't melt but it can splinter. It's a good idea to wear sturdy gloves when handling steel cable.
Next, we'll look at the physics behind using a winch.