Have you ever come up short on a rappel when you remember that you’d managed to make it before? How about tried to toprope a pitch only to find yourself unable to lower a climber to the ground when others, with the same length ropes, had no problem? This might not simply be your memory going bad on you. There are significant differences in the lengths of ropes all labelled and sold as being identical. And these difference don’t just occur among various brands, but actually are apparent within brands and even matched pairs of twin and half ropes sold as sets.
I originally became aware of these major differences when trying to evaluate ropes based upon their weight, measured in grams per meter. I quickly realized that I couldn’t simply divide the rope’s weight (easy to measure) by its stated length, because none of the 8 different 60m ropes I tested was actually the same length as any other. The skinniest (and lightest, per-meter) rope wouldn’t necessarily weigh the least, since the manufacturer may have cut it longer. In short, I couldn’t evaluate the grams-per-meter because I couldn’t reliably know the number of meters. This inability to accurately weigh a rope proved especially frustrating, because evaluating a rope based on the advertised diameter is the only real alternative, but this relies on trusting the self-policed measurement of a company whose interests lie in selling you their new ultra skinny rope. And these measurements are made with calipers which can easily pinch down a few millimeters onto the rope, yielding an inaccurate measure. Furthermore, some ropes have an immediate tendency to expand and puff out when used, making their initial diameter especially irrelevant. The weight, measured in grams/meter, was clearly the best option. I just had to know how many meters my 60m ropes were.
I drug a pile of more than 10 different ropes to a nearby high school tennis court, and was able to use the painted lines to measure out approximate distances for all my cords. Note that none of these measurements were made when the ropes were being weighted or sen hung vertically, so they would certainly allow for rappels longer than 1/2 of the lengths listed below. But in the end I was amazed at the differences among these ropes, both in terms of their lengths and their weights. All of these ropes are also used, and some have been used for years. The measured weight may include some dirt and another alpine debris gathered over the course of a few seasons of use, but even this is useful to measure, because if particular models are more prone to collecting dirt and gaining weight, that information is worth knowing.
It’s easy to see why some local pitches (Thin Fingers for 70m ropes immediately comes to mind) seem to be the site of frequent accents or near-misses, when climbers swear their rope will be long enough to set up a TR, because they correctly remember being able to do so in the past. Some “70m” ropes work, and others don’t. The takeaway for rope evaluating and rope-buying users is to try and weigh the ropes yourself, before buying, and without simply relying on the published weight. Ask to un-spool and compare the lengths of ropes you are considering buying, so you can know if that additional weight is due to a heavier rope, or merely a longer one. And learn which of your pair of twin or half ropes is actually longer, and thread that rope through the anchor on any rope stretching rappels. Using all the rope you’ve got with you is the next best thing to having a 62-meter “60m” when you remember your rappel just barely touches down.