Thick vs. Skinny Ropes

Hi everyone,

I was checking out Edelrid’s upcoming “Swift Protect Pro Dry” rope recently and began to wonder about the virtues of larger vs. smaller diameter ropes, assuming abrasion resistance is equal. 

For example, say we have two ropes: an 8.9 and a 10.2. For the sake of the thought experiment we will imagine their abrasion resistance to be identical (I am not exactly sure what Edelrid’s claim here is in regards to their rope, but it is similar). Would there remain any real advantage in using the thicker rope? I can think of two reasons, and I’m curious if anyone else has anything to add, or if anyone thinks that my reasons are irrelevant. These are:
1. A thinner rope will be more likely to get tangled.

2. A thinner rope will stretch more in the event of a fall and/or simply being weighted. (In regards to the Edelrid rope, however, this will be mitigated due to the aramid in the sheath causing the rope to be less stretchy than a comparable rope sans aramid).

It used to be that thicker ropes held more of their total strength in the core (e.g. 15% in the sheath, 85% in the core for an 11mm, while a 9mm was about 35% in the sheath and 65% in the core).  As ropes get thinner, a greater percentage is in the sheath so one would assume the overall strength would decrease faster with sheath wear.  That was then.  I don't know if sheath thickness has changed and correspondingly, the strength rations have changed over the last decade.

Artem Vasilyev wrote:

Thin ropes wear out quickly where it bends over a carabiner or any other hardware. So if you're dogging a route on a thin rope it will be toast very soon. Thats the greatest disadvantage. 

An inexperienced or overconfident belayer is more likely to drop you with a thin rope. Second greatest disadvantage.

From a safety perspective they are more likely to get cut, but only marginally so. Third greatest disadvantage.

The fact that they stretch more is actually an advantage in my experience, since they are more springy and reduce the fall factor on your gear and make it easy to get a soft catch.

Keep a thin rope for that RP attempt or for those long multipitch routes where you know you won't fall and don't want to hump a monstrosity of a rope around. Thick rope (9.8 is plenty) for dogging and TRing. Thin ropes do tangle more, but I've only noticed this as significant once you drop past 8.5mm range or so.

Thanks for the reply. 

1. That makes sense but I’m curious what exactly is being worn out here? Is the core of the rope losing its strength?

2. That’s a good one.

3. Assuming abrasion resistance is the same, this would be irrelevant, right? Or could it be the case that in the event of a core shot, the 10.2 will have more of a core to withstand further abrasion (in the event of a second falling on a roof and dangling in the air, with the core continuing to contact the rock as the climber is dangling, for example). 

As for stretchiness, I suppose the advantages and disadvantages will be situational. 

Artem Vasilyev wrote:

1) The core gets worn and floppy.

By "worn" do you mean core filaments are actually breaking?  Or do you mean that the sheath wears and gets looser and doesn't bind the core filaments as tightly?  It would seem to be the sheath that gets the wear from abrasion.

1. thin ropes have trouble in older belay devices
2. you can't switch from a 10.2 rope to an 8.9 and not adjust the rest of your systems. (ex. climber uses 7mm cord to create prussik on 10.2 dia rope. the same prusik would not grab so well on an 8.9)
3. with the same belay device, thinner ropes can be more difficult to hold a climber (ex. the effort required to hold someone hanging on a 10.2 with an atc is less than the same climber on an 8.9)

note: i have no actual data to support my 3rd point aside from my experience.

Joel M wrote: Hi everyone,


2. A thinner rope will stretch more in the event of a fall and/or simply being weighted. 

This is false according to the specs of most thinner ropes.   The opposite is true. 

Also, thinner ropes obviously have less surface area. So, any given spot on the rope will receive more abrasion for equivalent amount of use compared to thicker rope. 

According to a video by ukclimber the edelrid swift protect pro will be about 50% more cut resistant that their 9.8mm rope.  I bet it will be more abrasion resistant too.

I have been climbing primarily on mammut serenity 8.7 and older 8.9 for 7 years.  It is a great rope and seems as durable as my previous 9.6 and 9.8 mm ropes or even 11mm ropes from 40 years ago.  Stretch is similar to my other ropes reflecting the stretch specifications.  It is rated for fewer falls than thicker ropes so i suspect repeated sport falls would core shoot it quicker than a thicker rope.  I trad climb and rarely take a lead fall so that is not an issue for me.

The videos also say that rope diameter is a factor in cut resistance but not the most important factor.  Basically edelrid says there is no way to know the relative cut resistance of ropes.  They are developing a test for cut resistance and trying to push it on the industry.

As stated above, you must adjust the rest of your system to match your rope; especially the belay device. 

Hobo Greg wrote:

Exactly, and if you look at my tick list, you'll see that 5.8 and under is 80% of what I climb!

a man after my own heart!!!

This thread may be relevant:
https://www.mountainproject.com/forum/topic/117828472/skinny-ropes-thoughts-on-failures-and-real-world-safety