You may be wondering, does it really make that much difference if I use a pulley or a carabiner?

Short answer, it can make a lot of difference. Use pulleys whenever possible. We had a look at this above with the Sticky diagrams, but it's important to get this, so let's have a quick review.

Say you need to lift 100 pound load, with a 1:1 system redirected through a high-quality pulley which is 90% efficient, which is pretty typical for a standard rescue pulley. Here, you need to apply 111 pounds of pulling force to move the load. (The math for this is 100 divided by 0.9).

However, let's redirect that same 100 pound load through a carabiner, which has an efficiency of roughly 50%. Here, you need 200 pounds of pulling force to move the load. (The math for this is 100 divided by 0.5).

So, use a pulley and pull with 111 pounds, or use a carabiner and pull with 200 pounds? Easy choice!

Here’s a table of pulley efficiencies. You may have seen this in another post, but it’s important, so I’ll include it here again. This is for a 1:1 haul through a redirect point. (If that last sentence made no sense to you, read this post first.)

OK, so that's for 1:1 redirected pull. How about for a 3:1 hauling system?

Great question. Check out the series of four photos below.

• Top left: the most efficient system, with 90% efficient pulleys. MA of about 2.7 to 1, about as good as it's ever going to get.

• Top right, carabiner for progress capture, pulley on tractor. MA of about 2.4 to 1. Still not bad!

• Bottom left, pulley for progress capture, carabiner on tractor. Disappointing MA of about 2 to 1.

• Finally, bottom right, carabiners in both places. Lousy MA, about 1.8 to 1.

A few thoughts on this . . .

• My calculations use a pulley efficiency of 90% and a carabiner deficiency of 50%. (Yes I rounded off in a couple of places, don't beat me up on the math.)

• It's clear that having a pulley closest to the hand that is applying the pull is the best way to rig.

• Many people think that you should always put the pulley closest to the load. That is obviously not true.

Here’s a chart takes a little deeper dive into this for different systems.

With an MA system of 3:1 and only use 50% efficient carabiners, your real world MA is going to be about 1.75:1, ouch! (Plus, you still have the dismal progress of a 3:1, with only 1 foot of lift for every 3 feet of pull, even though you're pulling harder than you should have to.)

In this case, you may be better off using a 2:1 with one good pulley than a 3:1 with carabiners! We can see from the chart that a 2:1 with 20% friction (i.e., a 80% efficient pulley) gives us an MA of 1.80:1. But, a 3:1 with carabiners gives us an MA of 1.75:1.

So, use real pulleys whenever possible.

If you have to use a carabiner, which kind is best?

I’ve heard over the years that generally, a carabiner with round metal stock is is going to be more efficient than the new style “I-beam” construction with a narrower cross section. But is it really? if so, how much?

Here’s a Camp Nano carabiner on the left, and an old school Petzl Attache carabiner on the right.

What about the DMM Revolver carabiner?

The DMM revolver carabiner is a cleverly designed piece of gear. It’s a standard snapgate carabiner with a tiny roller wheel in the bottom. The Revolver carabiner was designed to minimize rope drag when lead climbing, not serve as a proper pulley in a block and tackle system.

Many people think (hope?) they can use a Revolver to lighten up their rescue kit, but unfortunately it doesn't work. I don't know precisely why, but I think the pulley wheel is so small that under any significant load, it's sort of compresses and you end up with an efficiency pretty much the same as a standard carabiner. I actually tested it and found about 50% efficiency.

If you want a proper combination carabiner and quality pulley, check the Petzl RollClip (or Edelrid Axiom). It has a more substantial pulley in the bottom and works as advertised under load. It’s not used much by recreational climbers, but it's common equipment for rigging and rescue professionals.

I couldn’t find any sort of formal testing online that showed this, so I decided to try a little observational study myself. 

Components: 

• 10 pound barbell weight

• Digital spring scale (about $11, I used this one)

• 9 mm dynamic rope

• Old style Petzl Attaché carabiner (rounded)

• New style Camp Nano carabiner (I-beam)

• brand new rescue pulley

I tied the barbell onto the end of the rope, ran the rope through the carabiner on a bolted anchor to get a 1:1 with a redirect, clove hitched another carabiner in the pull strand and clipped the spring pulley to the carabiner.

I tried to pull straight down in a slow steady haul, and noted the most common reading on the scale. Any force over 10 pounds shows the inefficiency of the system.

• Force needed with rescue pulley (baseline): 13 lbs - 77% efficient

• Force needed with rounded carabiner: 20 lbs - 50% efficient

• Force needed with a “I-beam” carabiner: 23 lbs - 43% efficient

(Math: 10 / 13 = .77; 10 / 20 = .50, 10 /23 = .43)

So, the rounded Petzl carabiner gives a slightly easier haul. (Note, this result was spot on with the often stated 50% efficiency rating of carabiners.)

Would you notice that extra bit of inefficiency in the real world? I’m not sure. But, if you have the option to use a round stock carabiner over an I-beam type carabiner use the round stock. Every little bit helps, right?

(Also, just for fun, I rigged two identical Petzl Attache carabiner side by side. The force needed to lift these was just 21 pounds, basically the same as the single Petzl Attache carabiner. In this case, adding one more carabiner really did not change the friction one way or the other.)

Now, something that definitely ventures into engineering-land that is beyond the scope of my expertise is something called “coefficient of friction”, which is a technical way of measuring how “slippery” something is. From my limited reading on this, the coefficient of friction for steel is different than that of aluminum, so apparently a steel carabiner will offer less friction than an aluminum carabiner. I don’t have a steel carabiner or else I would’ve tested this, it would have been interesting.

So, in summary, use a pulley if you have one!