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How accurate is advertised rope weight?


Original Post
SteveF · · Fort Collins, CO · Joined Aug 2007 · Points: 33

My new Mammut Infinity 60 m dry duodess weighs in at 65 g/m on my kitchen scale. This is about 10% heavier than the advertised weight of 59 g/m. Mammut responded to me with pretty reasonable explanation that delivered weight can be greater than production weight because they add 2.5 m to ropes to account for shrinkage over the life of the rope and because of absorption of atmospheric moisture.

Still, I was expecting a lighter rope, and I'm wondering if this discrepancy between delivered weight and advertised weight is common across models and manufacturers. How does the weight of your new rope compare to what was advertised?

SinRopa · · parts unknown · Joined Sep 2013 · Points: 50

Is the 2.5m thing accurate? Is your 60m really 62.5m?

20 kN · · Unknown Hometown · Joined Feb 2009 · Points: 1,348
SteveF wrote:My new Mammut Infinity 60 m dry duodess weighs in at 65 g/m on my kitchen scale. This is about 10% heavier than the advertised weight of 59 g/m. Mammut responded to me with pretty reasonable explanation that delivered weight can be greater than production weight because they add 2.5 m to ropes to account for shrinkage over the life of the rope and because of absorption of atmospheric moisture. Still, I was expecting a lighter rope, and I'm wondering if this discrepancy between delivered weight and advertised weight is common across models and manufacturers. How does the weight of your new rope compare to what was advertised?
2.5m would make the rope 61.4g/m, not 65. I weighed my brand new, never used Maxim Pinnacle 9.5mm and it is only 0.75g/m heavier than its advertised weight of 61. It's sat on a shelf in a city known for humidity for a year. I also weighed a well-used Maxim Pinnacle (after wash and dry) and it clocks in at 2.5g/m heavier than advertised.
John Wilder · · Las Vegas, NV · Joined Feb 2004 · Points: 1,530
SinRopa wrote:Is the 2.5m thing accurate? Is your 60m really 62.5m?
Yes. Many manufacturers cut ropes long to account for shrinkage as the rope ages. Some don't.
SteveF · · Fort Collins, CO · Joined Aug 2007 · Points: 33

I have no way of measuring my rope to make sure that's its 62.5 m, but I'm guessing that it is.

It seems like the remaining weight difference is still quite a lot, especially in Colorado which is generally pretty dry, but I'm not really sure how much atmospheric moisture should increase the rope weight to begin with.

Em Cos · · Boulder, CO · Joined Apr 2010 · Points: 5

The advertised rope weight is a per meter weight, not a total weight. You can't know if that weight is off or by how much if you only know your rope's total weight and don't know its length.

Pavel Burov · · Russia · Joined May 2013 · Points: 50

1. Scales. There are no absolutely precise scales. This is the 1st effect to consider.

2. Weighting the scales. Some scales are sensitive to weight positioning. This is the 2nd effect to consider.

3. Water. There are a decent amount of water in the air around us. Ropes are somewhat hygroscopic (even double dry ones). Air humidity changes could affect textiles weight. This is the 3rd effect to consider.

4. Ropes materials variations. Yet another effect to consider.

5. Ropes technology variations. Merchandises descriptions are almost always include a string (printed in the smallest type size available) like "Manufacturer reserves the right to change blah-blah-blah without prior notice". Yet another effect to consider.

6, 7, 8, 9, 10, etc.

Em Cos · · Boulder, CO · Joined Apr 2010 · Points: 5
Greg D wrote: Wow. You are really good at math.
Not sure why that was warranted... the OP seemed concerned that his rope weight was off, but also seemed to be calculating it by ";guessing"; that it's 62.5 meters. Just pointing out that it may be the length that's off rather than the weight, and that worrying about the weight being off doesn't make much sense if you don't even know yet whether it is. If that's not a helpful observation, feel free to ignore it.
SteveF · · Fort Collins, CO · Joined Aug 2007 · Points: 33
Em Cos wrote:The advertised rope weight is a per meter weight, not a total weight. You can't know if that weight is off or by how much if you only know your rope's total weight and don't know its length.
The manufacturer told me they cut their ropes 2.5 m longer, and the weight would still be greater than the advertised weight either way.

I was kinda hoping more people would weigh their ropes so we could see what the differences commonly are between the advertised weight and the delivered weight for different models and manufacturers.
John Wilder · · Las Vegas, NV · Joined Feb 2004 · Points: 1,530
SteveF wrote: The manufacturer told me they cut their ropes 2.5 m longer, and the weight would still be greater than the advertised weight either way. I was kinda hoping more people would weigh their ropes so we could see what the differences commonly are between the advertised weight and the delivered weight for different models and manufacturers.
True, but I would still measure your rope for an accurate length. Mammut cuts ropes by machine, so its probably pretty close to 62.5m, but it could be a bit longer depending on what the setting on the machine is.

Sterling can give you up to 5m of rope (i've had 65m ropes from them).

Edelrid cuts their ropes exactly at the length advertised. (Petzl may have Edelrid do the same, but I can't speak directly to that)

Not sure how the other manufacturers address shrinkage.

At any rate, the length past that listed on the packaging isn't required of the manufacturer, so it really could be anything. If it was at the end of a run, Mammut may have cut your rope 5m long- or 3.2, or who knows?
Martin le Roux · · Superior, CO · Joined Jul 2003 · Points: 234

FWIW here's what I get with a consumer-grade digital scale. These ropes have all seen moderate usage.

Mammut Twilight 7.5mm 70m: 41 g/m (manufacturer claims 38 g/m)
Edelweiss Oxygen 8.2mm 70m: 48 g/m (manufacturer claims 45 g/m)
Beal Rando 8.0mm 20m: 41 g/m (manufacturer claims 37 g/m)

So all about 3-4 g/m heavier than advertised.

My guess would be that it's combination of ropes being longer than stated, water absorption and measurement error.

20 kN · · Unknown Hometown · Joined Feb 2009 · Points: 1,348
Martin le Roux wrote:FWIW here's what I get with a consumer-grade digital scale. These ropes have all seen moderate usage. Mammut Twilight 7.5mm 70m: 41 g/m (manufacturer claims 38 g/m) Edelweiss Oxygen 8.2mm 70m: 48 g/m (manufacturer claims 45 g/m) Beal Rando 8.0mm 20m: 41 g/m (manufacturer claims 37 g/m) So all about 3-4 g/m heavier than advertised. My guess would be that it's combination of ropes being longer than stated, water absorption and measurement error.
If they are used they are going to contain dirt and aluminum. You need to wash them and let them dry completely before obtaining an accurate measurement. I suspect if you do that the weight will drop slightly (as it did in my case).
mbk · · Unknown Hometown · Joined Jul 2013 · Points: 0

You have to weigh the rope while you are hanging on a full rope length of it.

Mammut claims static elongation of 6.8%.

So your "62.5m" rope is really 66.75m long. Thus it really is only 58.4g/m.

PS: this is why they call it "weighting the rope"

PPS: I was only kidding but the math works out (and the units are right, so the legions of armchair physics experts should be convinced...)

20 kN · · Unknown Hometown · Joined Feb 2009 · Points: 1,348

You have to weigh the rope while you are hanging on a full rope length of it. Mammut claims static elongation of 6.8%. So your "62.5m" rope is really 66.75m long. quote>
No it's not. Static elongation is the stretch of the rope with 80kg hanging on it. This has nothing to do with weight anyway. Stretching the rope does not make it lighter or heavier. Yes, the rope would be 66.75m long with 80kg on it, but that's irrelevant as weight is not measured per meter when the rope is weighted. It's per meter of unweighted, unloaded, unused rope.

Jonathan Awerbuch · · Boulder, Colorado · Joined Nov 2013 · Points: 38
mbk wrote:You have to weigh the rope while you are hanging on a full rope length of it. Mammut claims static elongation of 6.8%. So your "62.5m" rope is really 66.75m long. Thus it really is only 58.4g/m.
clever
PRRose · · Boulder · Joined Feb 2006 · Points: 0
20 kN wrote:You have to weigh the rope while you are hanging on a full rope length of it. Mammut claims static elongation of 6.8%. So your "62.5m" rope is really 66.75m long. quote> No it's not. Static elongation is the stretch of the rope with 80kg hanging on it. This has nothing to do with weight anyway. Stretching the rope does not make it lighter or heavier. Yes, the rope would be 66.75m long with 80kg on it, but that's irrelevant as weight is not measured per meter when the rope is weighted. It's per meter of unweighted, unloaded, unused rope.
But at what temperature and relative humidity?
Pavel Burov · · Russia · Joined May 2013 · Points: 50
PRRose wrote: But at what temperature and relative humidity?
At least one more important parameter to consider: pressure.
SteveF · · Fort Collins, CO · Joined Aug 2007 · Points: 33

It looks like a few other ropes also have advertised weights that are greater than their delivered weight. I guess it's good to know that mine isn't a complete anomaly.

After this I'm wondering if I should even consider weight as an important factor when choosing a rope because I'm unlikely to get what I expect. If there was a consistent bias across ropes then it would still make sense to choose a rope based on weight, just expect 3-4 grams over whats advertised. But, if the differences are more variable and possibly due to more than just extra length and moisture, as some have suggested, then maybe deciding between ropes based on small weight differences is pointless. Or maybe there should be some more well defined standards for advertising rope weight since the recent craze over thinner and supposedly lighter ropes suggests that weight is very important to a lot of people.

SinRopa · · parts unknown · Joined Sep 2013 · Points: 50
Pavel Burov wrote: At least one more important parameter to consider: pressure.
Also, distance from the Earth's core. The weight of a rope decreases inversely as the square of the distance of the rope from the core increases. So, the rope will weigh less when you're 5 pitches up as opposed to on the ground.
Robert Hall · · North Conway, NH · Joined Aug 2013 · Points: 12,413

I believe that I once read that the weight per meter is calculated as follows:

1) The rope is hung vertically
2) a 10 kg weight is attached to the bottom. (Yes, Virginia, that means there's some stretch placed in the rope; but this is done "so as to make sure all ropes are treated alike." DUH !)
3) An exact 1 meter length is marked and cut.
4) The cut piece is weighed, reported to the nearest gram per meter. (i.e. 58.7 is 59g/m ; 58.4 is 58g/m

You can probably find the exact method used in the UIAA regulations on rope weight. Certainly, somewhere in the millions of pages of EC regulations the test is also given.

A far larger problem, in my opinion, is rope shrinkage during use, and what factors affect it and which ropes are more prone to it. My 70m is now 62m long.

PRRose · · Boulder · Joined Feb 2006 · Points: 0
20 kN wrote: I dont know what there is to standardize. The process of weighing a rope is literately so simple a kid could do it. I doubt relative humidity matters that much. Maybe the difference between 0% and 100% is noteworthy, but going from 40% in the factory to 70% in your house is not going to do much. If you want to find out, grab a bunch of clean, unused clothes from your drawer, weigh them, then put them in the dryer to remove any humidity and weigh them again. That would give you an idea, although nylon will absorb much less water than nylon, so the effect would be amplified with cotton clothes. As far as the rope being longer, if it is longer the entire rope is heavier but the weight per meter is not greater than if the rope were shorter. If the numbers are really off, I think the most obvious conclusion would be that the manufacturer is not providing truthful data. That's not exactly a stretch considering considering how often companies pad the abilities of their products in order to make the product sounder better than it actually is.
Nylons would absorb approximately 2% by weight of water between 40% and 70% humidity.
Guideline #1: Don't be a jerk.

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