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Brake Slippage Test


There has been a lot of talk lately about how different brakes are slipping with different sizes of rope and under different loads. So, I thought I would test the 6 different brakes that I own (besides the MPD) with a variety of different sized ropes to see just when each brake would start to slip.



I found a place in my local park that had 2 trees spaced at about 15 feet apart and set up two anchors. I attached the end of the rope with a figure-8 knot to one anchor, then attach the other end to the brake that I was testing. I then attached the hook from my small chain hoist to the brake and had that connected to my dyno. I then proceeded to tension the rope up to about 1200 lbs, or whenever the brake started to slip.

The 6 brakes that I tested were:

  1. CT Sparrow
  2. Petzl I'D
  3. Petzl RIG
  4. Edelrid Eddy
  5. Petzl GriGri 1
  6. Petzl GriGri 2

I tested 3 different rope sizes with each of these 6 brakes: 11mm, 10mm, and 9mm. Each of these ropes had similar characteristics and the same sheath construction, so the only variables were stretch and size.



Here is a nice table that shows the results from the test. Keep in mind that when I say no slippage, this was only up to about 1,150 - 1,250 lbf. Also, the numbers below indicate when the brake started to slip.


Brake 11mm Rope 10mm Rope 9mm Rope
CT Sparrow No Slippage 590 lbf 250 lbf
Petzl I'D No Slippage 680 lbf 340 lbf
Petzl RIG No Slippage 700 lbf 400 lbf
Edelrid Eddy No Slippage 850 lbf 420 lbf
Petzl Grigri 1 900 lbf 670 lbf 375 lbf
Petzl Grigri 2 No Slippage No Slippage 900 lbf



These results are very surprising to me. I am quite surprised at how badly the CT Sparrow did with smaller diameter ropes. However, it was designed for 10.5mm - 11mm ropes, so that shouldn't be that big of an issue. What also surprised me was how well the GriGri 2 performed. I was under the impression that this device was of poor quality. But, it was designed for a large range of rope sizes, so I guess it makes sense.

All the devices performed excellently with the use of 11mm rope. This goes to show that this size of rope is best for pulley systems. You won't ever experience slipping and your system will be super strong at the same time. I typically only use 11mm rope for most of my pulley systems.

Some things to note:

  • All the ropes I used had the same sheath construction. So, if a rope has a different type of sheath, it may perform differently that the results above.
  • The temperature outside was around 60-degrees Fahrenheit, which has an effect on the results. If it is hotter outside, or the humidity is higher, you may experience more slippage compared to a cool, dry day.
  • The amount of use that each of these brakes has varies significantly. This could definitely affect the results of a test like this. This could be why the Sparrow performed so badly. I believe that once it has been used a few times, the friction will become better.
  • IMPORTANT! All these tests exceeded the capacities of these braking devices. This should NEVER be done at home. It can have a very negative effect on the strength of the device and compromise its ability to hold much force. Do not exceed the working load limit of your gear!


Future Research

I would like to vary the sheath types and also the heat/humidity to get a better idea of how these devices perform across the board.

Here is a video of the test:

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18 thoughts on “Brake Slippage Test”

  • Daniel Chenoweth - January 20, 2014 at 8:15 am

    What multiplier pulley were you using when finding the total system efficiency of the 15:1 systems in the graphs above?

  • I'd love to see some data points added in for one of these systems, using an MPD instead of the fixed cam brakes!

  • Great post and very useful test. It's worth noting that I had the Eddy slip recently during some filming in which a dyno was in the system (so I can speak to the brake tension as a result of mechanical advantage). Using an 11mm rope, the Eddy was slipping lightly at around ~500-550lbs of tension. This rope may have been particularly "slippery" and I am hoping someday to repeat the rigging using an I'D and the same rope (assuming my friend, who owns the rope, will participate). So my comment here would be to reinforce Jerry's comment that the above results are probably able to be extrapolated to other users' rigging (as far as which devices slip more easily) but that any given rope may vary a lot from the results documented and this should be taken into account (i.e. backups in place, not assuming that "because the Sparrow isn't slipping yet with this 9mm rope I can know the tension isn't over 1250lbs" etc). I have, for instance, heard lots of talk of GriGri 1 slippage for people rigging lines in the 100M range, yet Jerry's results imply 4000+lbs of tension necessary for this. I suspect there is a lot of variation in maximum static friction (the maximum load the brake can endure before the rope begins to slip) from system to system. Video of the Eddy slipping can be seen in the to-be-published-any-day-now final installment of the NWslackline Guide to Longline (Part 5).

    • Was the slip you encountered slow or fast? I've put some serious tension on my Eddy with 9mm rope before and not had it slip.

      I imagine that the act of pulling the rope through the device will effect the way it holds tension as well. Maybe a more rapid tensioning would result in more slippage due to higher heat within the brake. Not sure about this though.

      Also, it's important to note that the tensions I displayed above are directly on the brake, not on the whole system. The brake only holds 1/5 or 1/9 of the full tension on a typical slackline rig.

  • Which rope do you use? (manufacturer, product name, ...).
    Please consider that this is a very important part in the setup, and the results may differ drastically!

    For instance: with 9mm Super Static from Edelrid , Edelrid Eddy as brake, and 3 inch SMC pullys (5:1 base) , we meassured a slippage at 15 kN, which differs from your results about 50% !

    If we don´t take all the important things into account, we don´t have to test anything, because the results aren´t that clean.
    It would also be nice if the test examples (brakes in this test), would be comparable in abrasion, age, and so on.

    • All three ropes were from PMI. The 9mm was classic professional static, the 10mm was the same, and the 11mm was the Access Pro.

      I realize this test was not perfect, but I used what materials I had on hand. The results were definitely affected because of this. However, since the ropes were the same across the board, the results do have some relevence.

      Also, I agree that the samples (brakes) should have the same use, but I do not have access to brand new items for each of the samples, so I used what I had.

      • Please don´t get me wrong, I really like to see somebody starts with tests of that kind! I just wanted to point the things out that aren´t clear for me and differ from our own tests.
        If we put all the informations we have together, we could have a very clear view of what equipment is the best for what requirement. This is what counts.
        I look forward to the next tests.

      • I think the results are still very useful regardless of flaws. Imperfect data is better than non-existent data, hearsay or anecdote. For example, the data tells us precisely what load each of those brakes CAN slip at in a given real world scenario. In the real world, nobodies gear is new after the first use anyway. Data on gear in "in-use" condition is in someways more relevant than fresh-out-of-the-box condition, even if it makes comparison less precise.

  • Christian Katlein - January 29, 2014 at 11:39 am

    Nice tests! You name your section Slack-Science, as in Science one has to use SI-Units it would be great if you can give your Force readings in kN, to make your observations more widespread!

  • Daniel Chenoweth - January 29, 2014 at 11:40 am

    Given that the Eddy slipped at only about 420 lb ft (2,100 at the line), what sort of WLL/ comfortable max tension would you use with the eddy and 9mm rope? I want to get a smaller diameter and shorter piece of static rope to go with an Eddy and my SMC's for a lighter 5:1 system that can still reach 12 kn. Should I get 10mm rope? 10.5? 11?

  • Ryan Morse-Brady - January 29, 2014 at 11:40 am

    I really like this test, and appreciate the information. I would like to add a few of my own findings, and hope they might add to the discussion:

    [1] Our setup includes 100' of ClimbSpec webbing and a dynamic Sterling 9.8 (retired climbing rope), which creeps significantly regardless of line length. We generally have to tension our line to relatively high degree, as one of my slacking partners is 240lbs, so this may play into the slippage. However, there is noticeably less "creeping" of the line when it is just my wife and I. [NOTE: All of the sessions that this applies to occurred in Tucson, AZ, at temperatures ranging from 85-100 degrees Fahrenheit, during monsoon season, with about 20-40% average humidity.]

    [2] We recently tried to instead use some 11.1mm (7/16") Bluewater 2 static cord, but it caused the Eddy to jam before we could pull the line tight. We are thinking of trying again with 10mm static cord, but are wary of purchasing any before verifying that it will work without slippage or jamming. Any recommendations?

    • I've only really tried using dynamic rope in a pulley system one time and that was just for a test. It would seem like the elasticity of the rope shouldn't have an affect on the slippage of the brake. However, the suppleness of the rope most definitely does. A more stiff rope will tend to slip much sooner than a more malleable rope. This could be the reason why your static rope was slipping before the dynamic: a change in malleability.

      I've never seen the Eddy jam up before. Are you sure you are loading it correctly? I use my PMI Access PRO 11mm Static Rope all the time and have never had any issues with jamming. I would try and use a very supple static rope, like the one mentioned above, if you are trying to maximize the holding power of the Eddy.

      • Ryan Morse-Brady - January 29, 2014 at 11:41 am

        Thanks for the response. The Bluewater 2 is at least 2x stiffer than the Sterling 9.8 dynamic. However it was definitely loaded correctly and it just jammed at after a certain amount of poundage pulled. I guess PMI 11 must have a quality that Bluewater 7/16th's do not (suppleness was suggested and probable). When I can afford it I'll have to order some PMI 11 and try again. I would bet that the dynamic rope slips because it's too supple and pinches much flatter when highly loaded, with my fingers I can squish used climbing rope by about 25%.

        • It issue with the dynamic rope is likely more a size issue rather than a suppleness issue. The fact that it's 9.8mm makes it more likely to slip. In order to get the maximum holding power out of the Eddy, you need a combination of a good size and a good suppleness, which the PMI Access PRO 11mm Static Rope seems to fit perfectly.

          When you say jammed, you mean that you couldn't tension any more and you also couldn't release?

          • Ryan Morse-Brady - January 29, 2014 at 11:41 am

            When it jams with the thicker stat rope I cannot pull more tension, nor will it release. I pull the handle and it does nothing (it feels hung up). I have to hold the knob down with my thumb and force it through. It's really strange and I'm glad it jams before too much tension is pulled.

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