Everyone knows it’s bad news when a carabiner is loaded over an edge.
Sure, it’s not ideal… but shit happens. Sometimes you find yourself looking at a levered carabiner. Maybe someone drilled a bad bolt. Maybe you’re placing a cam deep in a crack and don’t have a runner.
Regardless, when a carabiner is loaded over an edge, it reduces the strength of the carabiner. But by how much?
The Setup
If you want to watch how exactly we tested this, you can click on the video. But in short, we used a hydraulic system to pull a carabiner—clipped into a standard bolt hanger on the outside of our test bed—across the metal edge.
Usually, the load cell is on the opposite side of what we’re pulling, but that isn’t possible in this case (and we can’t put it behind the hydraulic because we aren’t set up for that). To solve this we measured the force with a LineScale-2 dynamometer and were careful not to let it go flying!
During the test, we also moved the metal plate with our hanger in relation to the edge, to mimic several angles.
REFERENCE: Climbing gear is rated in kilonewtons (kN). This is an expression of force, and the kN rating on your gear demonstrates how much force the gear can withstand. 1kN is equal to about 225 pounds (102 kg) under Earth’s gravity.
Test 1: Wiregates Levered Near Midpoint
Result: Carabiners break at 5.57kN and 3.69kN
In the first scenario, the plate our hanger was on was positioned further from the edge of the box, so the carabiner was initially levered nearly at the midpoint of its spine. It broke at 5.57kN.
We also used a second carabiner (of a different model), levered over the box edge itself. This carabiner was levered closer to the pull point, not directly on its midpoint. Still, it broke at a mere 3.69kN (830 pounds).
Even in the biner that held longer busted under a mere 5.57kN (1,200 pounds of force). You could probably achieve that in a whipper.
Test 2: Locker Levered Near Midpoint
Result: Carabiner breaks at 6.01kN
Even this burly, thicker locker broke at not much more than our wiregate in Test 1 (around 6kN) when levered at its midpoint.
Test 3: Wiregate Barely Levered
Result: Carabiner breaks at 18.44kN
This small wiregate, levered only barely over the edge, was much stronger. It broke at 18.44kN, which was nearly its minimum breaking strength (MBS) of 22kN!
Test 4: Wiregate Near An Edge
Result: Carabiner breaks at 18.11kN
In this test, we attached a wiregate directly to a locker, and had the former loaded when it was perpendicular to the edge, but not quite angled over it. Like the wiregate in Test 3, this biner held up pretty well, breaking at 18.11kN.
Test 5: Wiregate Levered on Spine
Result: Carabiner breaks at 4.65kN
When we positioned a wiregate and levered it directly onto the midpoint of its spine (as opposed to the gate-side and spine equally) it wasn’t any stronger. That said, it did twist and lie flat—loading along both sides—almost immediately, making the usefulness of this test hard to determine.
Conclusion
This was a simple test, with a very small sample size. We also used a metal plate and edges, which are likely sharper than the edges you’ll encounter on rock.
Still, our biggest takeaway is that when it comes to a levered carabiner’s strength, the size or thickness of the carabiner doesn’t matter nearly as much as the ANGLE at which it’s levered.
A tiny wiregate held up almost at MBS when it was just barely poking over the edge. A wiregate near the edge similarly performed nearly as well. But our big, burly locker broke at a paltry 6kN when we levered it over its midpoint.
What's Next
How Strong Are Levered Carabiners?
