Should I use a sliding x knot to equalize two pieces? [back to top] [FAQ contents]

From: Mike Garrison, 8/16/2001

It's like everything else involving anchors. There are times to use it and times when something else is better.

When you don't need dynamic equalization, don't use it. The dynamic equalization comes at direct cost of extension risk. When you do need dynamic equalization, use it. There are techniques (such as knotting the slings) that reduce the extension risk in direct proportion to how much they limit the range of dynamic equalization.

The question to ask is not "sliding X: good or bad?"; the question to ask is "do I need dynamic equalization in this case, and if so how much do I need?" A secondary question to ask is, "how much extension would there be in case of a failure, and what would catch how much force?"

If you consider all your options, you have a chance to pick the best one for the situation. If you only know/use one anchoring option, you will often not be using the optimal one.

From: the ASCA

Many climbers use a "sliding X" to equalize two pieces - ususally beginner climbers with bolt anchors. You should NEVER use this except in two specialized cases (see below). While the sliding X does equalize the pieces, it assumes that neither could break, since if one does break, there is severe extension in the system - enough that it would likely cause the carabiners to break. Since it assumes neither piece would break, it's a stupid system - if neither would break, there's no need for equalization. If one might break, then there is WAY too much extension. This is why many call it the "death X." Instead, use one sling off of each bolt or piece. You can tie one shorter to approximately equalize the pieces if needed.

The two cases where the sliding X is used:

equalizing tenuous pieces in a larger anchor - for instance, two poor nuts in a large natural pro anchor. The nuts are equalized, then the sliding X is equalized with other pieces through a cordelette, webolette, or other non-extending method.
equalizing two very tenuous pieces in extreme aid - for instance, a hook and a bashie on A4 terrain.

From: Greg Barnes, 7/8/2001

As I'm sure has been beat to death here in the past, you really shouldn't ever use the sliding X, except as a component of an anchor with no extension should one of the sliding X pieces fail (e.g. equalizing two poor nuts with the X, and then the X is one of three points of a cordalette) - or for equalizing dicey aid pieces. While the X equalizes better, it should only be used where both pieces are completely bomber, since if one breaks there is severe extension. Since you're using it with two bomber pieces, why worry about great equalization in the first place?

Anyway, just use separate slings on the different bolts (you can tie one shorter to approximately equalize if needed), and back up with another sling on the good bolt, all going to 2 or 3 biners, and you don't have to worry about it. But for a 2-piece anchor, dump the sliding X regardless. If you need to use it, it's too dangerous to use. If you don't need to use it, why make things complicated when one sling off of each bolt is better? It does look cool though, and that counts for something...

From: Ken Cline, 4/13/2000

I never rig my main anchor with a sliding knot, though I occasionally use one in a component of an anchor. Here are three reasons:

1) Extension of an anchor is a bad thing. It can be bad enough when one piece of a "no extension" anchor blows (this happened to me, leaving me hanging uncomfortably), I don't recommend adding more extension.

2) You lose redundancy with this method. If the sliding cordalette gets cut by an edge, you die. With a knotted cordalette, other parts of the anchor have to fail as well.

3) The carabiner connecting you to the anchor is subject to more acceleration and potential impacts with a sliding cordalette. If the carabiner is not locked, the gate is more likely to open, and even if it is locked, there is greater risk of improper loading.

From: Jay Tanzman, 8/16/2001

__ __ / \ / \ | A | | B | \ \ / / \ \ / / \ \ / / \ C / \ / \ / V v

Unless it is just the limitations of ASCII, your sketch suggests that you do not understand what a sliding X is. With a sliding X, the carabiner(s) is clipped into a single strand of the sewn sling (i.e., _through_ the sling), not around both strands of it. This is accomplished by placing a half-twist in one of the loops (say the one coming down from your 'B') and then clipping the carabiner through both the A and B loops. Since the carabiner is clipped into a single strand of the sling, if either the A or B bolt were to fail, the remaining bolt would still be available as a back up. I say "available" because the potential danger of the sliding X is that if one bolt fails, the resulting sudden extension in the system shock loads the remaining bolt, which could cause it to fail as well.

From: Alon, 8/16/2001

Yes basically... refer to your "Climbing Anchors" book by John Long, page 70... the only thing missing above is a half twist as noted in both the book and Jay's reply.

Per John Long again..."A proper twist in the equalizing sling is essential to prevent failure of the complete system if one peice fails. Always double check to be sure that this twist is in place." So if A or B fail, the system does not fail. Yes if you sling fails and you are using a textbook Sliding X the system would fail, that portion is not redundant.

Squish Guy, 8/16/2001

If the twist 'confuses' you there is another way to clip the sliding X:

__ __ / \ / \ | A | | B | \ \ / / \ \ / / \ \ / / \ C / \ / \ / V v

To illustrate with words: Separate the sling like this into two 'V's, and clip the rope biner *horizontally* through the 'X' at point C...

From: Hans Lehmann, 8/16/2001

It just seems to me that a sliding X is perfectly safe. IF one peice does rip then the 2nd peice would be shock loaded due to the 6-12 in of extension caused by the X. However that amount of force is still significantly less than that cuased by a lead fall. And we trust one bolt to hold during a lead fall, and IF it does not than, as you state, we expect the bolt below to hold, in spite of the now more than doubled force(compared to that of the first bolt) has to absorb. Which is equivelant to one bolt on the X giving out, only the second bolt only has to deal with 6-12 inches of force created, vs. 6-12 feet on the second bolt during the lead fall.

The force on your anchor is related to the fall factor, not just to the distance of the fall. Picture yourself clipped into two bolts with the sliding X configuration at a hanging belay; no ledges to speak of so your entire weight is supported by the two bolts. While you're justing hanging there waiting for your partner to hurry up and tie his shoes and begin climbing already, cosmic forces work against you and one of the bolts snaps. You've got about a foot of dynamic rope between your harness and the biners that form the middle of the sliding X. If you're using a double-length sling to form the X, the the fall distance is also about a foot, so you've got factor 1 fall, which is certainly not significantly less than the average leader fall. If you've got all your weight already on the anchor, then the knots in your end of the rope are already pretty tight and won't contribute that much to the dynamic properties of the whole mess.

MadDog, 8/21/2001

The real danger of extension is when the leader falls before getting a piece in, loading the belay anchor to the point that the weakest piece fails. If a sliding X is being used, the remaining anchor piece (pieces) will be shock loaded not only with the belayer's static weight but also with the dynamic load of the falling leader. Also consider that on walls, the static mass of the haul bag might need to be considered, let alone additional team members and the ever-growing mass of the poop tube.

From: Jay Tanzman, 8/22/2001

If the first piece failed under a dynamic load, the remaining piece would be subjected to a large force as well. In situations where the first piece is bad enough to fail (bolt is bad, rock is bad, climber who set up the anchor is incompetent), the second piece, which may be the only thing left protecting two lives, may be bad as well, and any shock load could cause it to fail, too. Thus, the "no extension" maxim.

From: Hans Lehmann, 8/15/2001

But let's not forget that the sliding X pretty evenly balances the load between the two bolts, so the chance of either one breaking is much less.

That being said, when I come upon two bolts for an anchor, I still usually just clip in with a bowline on a bight, one loop clipped to each bolt.

From: Brian Cheung, 6/14/2000

I use the sliding knot a lot with toprope anchors, and to minimize extension I back up a leg of the whole configuration with another sling. Now I know this has problems as well (limiting the range etc.) but hey, like everyone else has said, nothing is perfect.

From: Kreighton, 11/5/2001

Since I am not totally comfortable with the cordelette with an eight/overhand and its inability to equalize with small changes in load direction, I prefer the sliding x. However, the obvious weakness of the 'x' has been made clear, and I therefore rarely use the 'x' alone. One thing I've seen, and use when I want the performance, if you will, of the x but with the redundancy of the overhand/figure 8, is to use overhand tie-offs in each load strand of the anchor. For example, if you use the sliding x with two pieces, as close above the anchor point as you can tie them, tie an overhand in each strand leading from the pieces. I usually get the knots about an inch away from the tie-in point, which leaves some room for the anchor to equalize within a small range (I find it especially useful if I've built in a lower, oppositional piece I want to remain equalized as well), but you've dramatically reduced the amount of shockload that will occur if a piece blows or fails. At the same time, if the cordelette fails (breaks, comes untied), it won't be able to thread right out of the anchor.

From: aT, 11/5/2001

This is actually recomended in John Long's "Climbing Anchors" book. You have to be careful though- there is a possibility of the overhand knot coming to rest at the tie in point in the event of one piece failing. don't want the knot *on* the biner...

See also:

How do I tie a [whatever] knot? on Tradgirl

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