Line Luddites

The automotive world has seen dozens of advances in technology that have added to the cost of each vehicle, but which are so clearly superior that it made little sense to retain the old technology as a cheaper option. No modern carmaker would think of offering front drum brakes instead of discs to save a buyer some money, and no sane buyer would request them. The same goes for carburetors versus fuel injection, bias-ply tires versus radials, lap belts versus air bags—the list goes on.

Yet again and again on overland forum threads discussing winches and winching, a few people persist in recommending steel cable over synthetic rope—and not solely on the basis of cost. One recent commenter actually made the claim: “Steel line is more forgiving than synthetic for the inexperienced off-roader.”

I try to be as diplomatic as possible on such threads. However, whether or not it’s smart, many of those “inexperienced off-roaders” look to forums for advice, and telling them they’re better off using steel winch line brings to mind those old-timers who used to claim things like, “You’re better off not wearing a seat belt because you might be trapped if there’s a fire.” (Presumably this is the fire that breaks out after your head-on collision.)

I’ll be considerate of steel winch cable and grant that it has a couple of advantages. It is considerably cheaper than its synthetic equivalent—in fact, these days if you buy a winch with no cable already installed it should be easy to pick up a steel cable for nothing at all from someone who has switched to synthetic (I have a couple lying around myself somewhere*). Steel cable is also more resistant to being cut when tensioned over a sharp object such as a rock or a poorly fabricated bumper opening, and it is more resistant to internal abrasion damage if frequently immersed in mud or grit (and not subsequently cleaned).

And . . . that’s about it. On virtually every other count, especially the critical question of safety for the winch operator and his assistant, synthetic line is far, far superior. In fact, most competitive four-wheel-drive events have simply outlawed steel winch cable.

Why is synthetic safer? Three reasons: low stretch, low mass, and linear recoil. 

Both SK-75 Dyneema—the standard for high-quality synthetic winch lines—and steel cable stretch less than one percent under load. However, a Dyneema line weighs about one-seventh what an equivalent steel line does, so the stored energy released during a break is far, far lower. (100 feet of 5/16ths-inch steel cable = 18 pounds. Equivalent synthetic = 2.7 pounds.) Additionally, the twisted construction of steel cable means that as it breaks (a process that actually takes several microseconds as individual strands snap) it experiences a violent untwisting motion, which can cause it to flail wildly as it recoils. The 12-strand woven construction of Dyneema obviates this. Finally, of course, the sharp frayed end of a broken steel cable can do a lot more damage than the end of a pliable length of Dyneema.

Twelve-strand SK-75 Dyneema—strong, easy-handling, and safe. 

I once watched a synthetic winch line part from about 15 feet away. The vehicle involved was being winched up a short but steep and rocky slope as part of a trials competition, so the system was under full tension. It appeared the line was cut over a rock on the crest of the slope because there was no protective sheath over the line, and the operators neglected to lay down a protective mat. Whatever the cause, the result was utterly lacking in drama; there was barely even any sound discernable over the ambient noise. A soft pop, and the two ends simply sprang about five feet apart and fell limply to the ground. (Note here, however, that this lack of drama will occur only if there is no stretch or extra mass anywhere in the system. If you attach a synthetic line to a steel extension cable, you’ve introduced much more potential kinetic energy.)

It’s worth mentioning here that if your steel winch cable does break and manages to not delimb any bystanders, you’re pretty much dead in the water. You've lost whatever length of line is attached to your thimble or hook—five feet if you're lucky, 50 if you're not. You can use wire rope clips to repair the end, but you'll lose up to 20 percent of the rope's original strength—worrying if you've just broken it. If a synthetic line breaks, it can be respliced in the field to virtually full strength and put back in use (in fact you can knot it for a quick repair, although the strength will be reduced). And synthetic line doesn’t develop those nasty single-strand steel burrs, which can punch through a glove.

Other effects of the weight difference are not to be dismissed lightly. The extra mass of that steel cable is all the way out at the end of the vehicle, where its effect on handling and stress on the suspension is magnified. Just pulling 75 feet of synthetic line uphill to an anchor is a joy compared to the same task with a steel cable**. 

Respooling (or spooling for the first time) a nicely limp synthetic line is infinitely easier than doing the same with steel, which has a powerful tendency to twist and coil back on itself. Laying down winch line evenly and tightly is critical to subsequent smooth operation, to avoid tensioned line diving down through gaps in the lower layers. Duncan Barbour, ex-manager of the British Camel Trophy team, reports that the biggest drawback he sees with synthetic line is the tendency to not spool it under sufficient tension—its ease of handling can actually encourage improper technique. A new line should be spooled by pulling another vehicle up a slight incline, not by simply leaning back on the line as you feed it in. (Incidentally, there are a few videos floating around suggesting crossing the line over itself as you spool it, rather than laying it on in even, tight layers. Don't believe them.)

Much has been written and said about the temperature sensitivity of Dyneema. Indeed, when heated to around 175 degrees Fahrenheit, it begins to lose tensile strength. However, interestingly, once cooled it actually regains full strength. Not until heated beyond the critical point of around 275 degrees do you suddenly find yourself with a irretrievable blob of molten plastic. That lower mark—possibly even the higher one—can be an issue if your planetary-gear winch has a brake inside the drum. If so, you should freespool when pulling line rather than powering out, and use caution when reversing a vehicle down a slope, to avoid prolonged braking. (Thor Jonsson at Viking Off Road once had a fellow return a broken Dyneema line and demand a refund. Interrogation revealed that the guy had lowered a half-dozen of his buddies’ trucks in succession down a steep ravine using an internally braked winch—and also that the winch itself had burned out.) Many planetary-gear winches now come with external brakes, which eliminate the problem. It’s also not an issue with the spur-drive Warn 8274 or the worm-drive Superwinch Husky. If you already own a winch with an internal brake, you can buy a sheath that will help protect the inside wrap of the line.

Many modern winches, such as the excellent Warn 9.5xp, incorporate brakes outside the drum and will not overheat synthetic line.

Steel-cable Luddites like to frown and speak darkly about the chemical sensitivity of synthetic winch line. I can’t remember the last time I spilled hydrochloric acid on my winch, or dragged line through a pool of trichloroethylene, but this chart (courtesy Marlow Ropes) should ease your mind (HMPE refers to High Molecular-weight PolyEthylene, which is what Dyneema is):

What else? Sun exposure worries some; in fact, Dyneema is extremely resistant to UV degradation. If you park your vehicle in the open in Arizona and fret about it, get a winch cover. And yes—you should periodically maintain your Dyneema line. If you frequently winch in abrasive conditions—sand, mud—it pays to occasionally wash it in a bucket of mild detergent, sqeezing apart the braid to flush out debris (some people simply powerwash it at a commercial car wash, although this is not recommended).

Strands are easy to push apart to flush out debris when washing.

In use, make sure you avoid running the tensioned line over sharp objects. This requires envisioning the entire pull you’re going to make, not just the initial layout—angles change, and a rock safely out of the way when you begin might not be partway through. If you can’t avoid running the line over an edge, use the section of sheathing supplied on most Dyneema lines to protect it—and add a floor mat or something else as well if possible. Avoid standing on the line, as it grinds in abrasives. If you switch from steel line to Dyneema, make sure your fairlead, whether hawse or roller, has no burrs or rough spots (there’s absolutely no reason not to use a roller fairlead with synthetic line, spurious anecdotes to the contrary). The same goes for the winch’s drum and your pulley blocks. As with any line, the radius of a roller, hawse opening, or pulley should if possible be six times the radius of the rope. Avoid, for example, low-profile hawse fairleads that create a tight bend radius on side pulls.

Roller fairleads work perfectly with synthetic winch lines, as long as they're not burred from prior use with steel cable.

If you’ve winched with steel cable and switch to Dyneema, you’ll be amazed at the reduction in effort. If you start out with Dyneema and then have to use a winch equipped with steel cable, you’ll feel like you’ve been transported back to 1960—which you have. It’s time to move winching into the 21st century.


*If, God forbid, you decide on this approach, make damn sure your free steel cable is sized appropriately. You don’t want to spool a line off someone’s ATV winch onto your Warn M12000.

**Depending on whom you’re asking, you might be told that “cable” or “line” or “rope” is the only proper term for the stuff a winch pulls with. Look up definitions for each and it’s clear that any will do. I like to mix them up in the same paragraph so as to annoy everyone at least once.