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All About Pulley Systems - Part 4 - Rope Characteristics

After looking at the characteristics for our main pulleys, as well as the attributes for our brake, it's time to delve into the topic of what size rope and how long it needs to be for our pulley system.

First I would like to look at the different sizes of rope that we have to choose from. In the Balance Community Shop, there are two options for the kind of rope that you can get: 10.5mm PMI Global Professional and 11mm PMI Access PRO, both of which are very high quality ropes that work perfectly for all slackline pulley systems. Now, you are probably wondering what the difference between these two ropes is. Well, there are a few differences that can help you decide which rope is best for you.

The first, and most important difference between these two ropes is the diameter. A rope with a smaller diameter is lighter, more supple, and also not quite as strong (if made from the same fibers as the larger rope). What this means for pulley systems is that the smaller diameter rope is very usefull when weight is a serious issue. When you are rigging larger lines with bigger pulleys, the larger diameter rope's added strength becomes a necessity. For alpine highlines and shorter lines in the park where you are using your lightweight pulley system (i.e. your Rock Exotica Mini Machined Double Pulleys), the smaller diameter rope works perfectly. Also, when using smaller pulleys, the sheave width is typically a lot smaller than larger pulleys, so a smaller diameter rope will glide through the rolls a lot better.


Sheave Width

Another difference between these two types of rope is how they are constructed. The 10.5mm rope has what is called a 16 carrier construction compared to the 32 carrier construction of the 11mm. What this means is how many bundles of fibers are used on the sheath of the rope when weaving. The smaller the number of carrier's, the less bundles of fibers are used. For instance, a 16 carrier rope will have 16 bundles of fibers on the sheath (the outer protective layer of the rope). This usually means that the rope has a much higher abrasion resistance because the fiber bundles that provide the abrasion protection are much larger, which makes them harder to abrade through. A higher carrier number usually means the rope has a softer feel since the fiber bundles that make up the sheath are much smaller.

Rope Carriers

The 10.5mm rope above is built with a 16-carrier design which is entirely made from nylon fibers, which are known to have lower abrasion resistance compared to polyester. This rope will be significantly more stiff than the 11mm because of the lower carrier construction. However, the 11mm has a sheath made from polyester, which is known for having much higher abrasion resistance compared to nylon. This means the hand will be a lot softer and you will still achieve the high abrasion resistance inherent in the lower-carrier construction ropes.

 

Here's a nice table showing the differences between the two types of ropes above:

Attribute PMI 10.5mm Global PRO PMI 11mm Access PRO
Construction 16-Carrier 32-Carrier
Sheath Material Nylon Polyester
Core Material Nylon Nylon
Diameter 10.5mm 11mm
Strength 27.0 kN (6,069 lbf) 27.4 kN (6,227 lbf)
Weight 53 g/m 84 g/m
Elongation 3.0% @ 330 lbf 3.4% @ 300 lbf
4.4% @ 600 lbf
9.9% @ 1,000 lbf
Price $0.69/foot $0.96/foot


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