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When the rope snaps tight, gravity takes over. In a partnership where the heavy leader is much more massive than the light belayer, the lighter person often pays the price. You aren’t just catching a fall; you are getting launched into the air.
I have seen competent climbers freeze up, not because the route was too hard, but because they were terrified of the catch dynamics. They know that if their heavier partner falls, the kinetic energy will pull them violently upward toward the first bolt.
This rocket effect—often called the rocket-belayer problem—isn’t because you are a bad belayer. It is simply a math problem regarding weight imbalance. However, the Edelrid Ohm tackles this issue. It changes the physics-based friction at the first bolt, allowing a 130lb (60kg) belayer to safely catch a 200lb (90kg) leader without flying off the ground.
This guide explains how the belay device works in plain English and teaches you the specific Zero-Drag belay positioning you need to use so you don’t succumb to short-roping mechanics.
Why Is The Weight Gap A Safety Hazard?
The “Rocket Belayer” effect is exactly what it sounds like. When a heavy leader falls, their energy pulls on the rope harder than the lighter belayer can pull back.
This causes the belayer to accelerate rapidly upward. This isn’t just an uncomfortable ride. Unlike a balanced fall where the rope stretches and absorbs the energy, this weight discrepancy creates a collision course. The lighter belayer is pulled straight up, often hitting their hands or body against the first bolt or the rock face.
The German Alpine Club (DAV) safety guidelines regarding weight disparity state that the danger zone starts at a weight difference of just 10 kg (22 lbs). Once you cross that line—specifically in the 10kg-40kg range—friction devices aren’t just a nice-to-have; they are a safety requirement to prevent the belayer from losing control.
In the past, people used weight bags or sandbags to weigh the belayer down. The problem is that sandbags stop you from moving around, making you a static ground anchor. The Ohm fixes this by balancing the system while still letting you move, which is a huge step in mitigating common climbing risks for climbing couples of different sizes.
How Does The Ohm Alter Climbing Physics?
Think of the Ohm as a smart assisted-braking resistor that lives on the first bolt via a quickdraw, rather than on your harness. It separates your body weight from the force of the fall.
When the climber is moving slowly—like clipping a bolt or taking slack—the device hangs loosely. The rope runs through it easily. However, if the rope moves fast—like during a fall—the device acts as a lever and swings up.
This swinging motion forces the rope into a tight V-shaped friction groove (or V-groove friction). This creates braking resistance at the bolt before the force ever reaches you.
A detailed analysis of impact force reduction in sports climbing—supported by research from the Institute of Mechanical Handling and Logistics (IFT Stuttgart)—shows that this mechanism reduces the impact on the climber by over 30%. This saves the leader from a hard jolt. At the same time, it provides effective weight, acting as if the belayer is roughly 25kg (55 lbs) heavier than they actually are.
Pro-Tip: The Ohm creates a “Soft Catch.” It feels smooth for the leader, but it creates enough drag to keep the belayer near the ground. Don’t fight the initial lift; let the device take the heavy hit first.
This is different from the mechanics of assisted-braking devices like the Grigri. Those devices help you hold the rope, but they don’t stop you from getting pulled upwards. The Ohm solves the problem at the source.
Which Generation of Ohm Fits Your Needs?
There are two main versions you will see in an Ohm 1 vs Ohm 2 comparison. The Ohm II is built like a tank for the gym, while the new Ohmega is lightweight for outdoor trips.
The Ohm II (Generation 2) creates friction using a steel groove. It weighs about a pound (360g-470g depending on the Ohm draw) and has a heavy-duty build. It features a swivel dogbone (or swivel joint), which is a massive upgrade from the original version because it stops the device from twisting around. It also features a new button design to open the unit. This is the best choice for gym climbing where weight doesn’t matter much.
The Ohmega (Generation 3) is a totally new design. It uses a fabric sling instead of metal links, dropping the weight to just 190g. This makes it perfect for hiking to outdoor crags. It also uses a pulley wheel, which makes feeding slack much smoother.
| Ohm Series Comparison | |||
|---|---|---|---|
| Feature | Ohm I (Original) | Ohm II (2020 Update) | Ohmega (2024/25) |
| Weight | ~470g | 450g | 190g |
| Mechanism | V-Groove Resistor (Rigid Assembly) | V-Groove Resistor with Swivel Joint | Integrated Pulley with Dyneema Sling and Camming Geometry |
| Adjustability | Fixed (~25 kg friction) | Fixed (~25 kg friction) | 3 Levels (Tunable to 10kg, 20kg, or 30kg) |
According to the Manufacturer specifications for Ohmega weight and rope compatibility, the new device allows you to adjust the braking power. You can set it to 10kg, 20kg, or 30kg of resistance by changing how the sling is clipped. This lets you tune the device: use max braking for big weight gaps, or less braking for smaller gaps. Both versions work with single ropes in the 8.9mm–11.0mm ropes range.
When assembling your essential climbing gear, the choice comes down to where you climb. If you hike long distances, the Ohmega’s light weight is necessary. If you stay in the gym, the Ohm II’s durability wins.
How Do You Master The “Zero-Drag” Protocol?
The biggest complaint people have with the Ohm is that it locks up when they try to feed slack, causing clipping drag. You can fix this by changing where you stand.
You must stand about 1 meter (3 feet) back from the wall, slightly to the side of the bolt line.
If you stand directly underneath the first bolt, the rope makes a sharp angle that pulls the device into the “lock” position (the Ohm engagement angle). By stepping back, you open up that angle. This keeps the device neutral so the rope can slide through.
You also need to use a “Soft Hand.” Feed slack smoothly. If you yank the rope quickly and explosively, the device thinks the lead climber is falling and it will lock. Consult the Edelrid Ohm user manual and operational warnings for pictures on how to hold the rope.
Pro-Tip: If the device locks while your partner is clipping, do not pull harder. Perform a “Jiggle Reset.” Send a small wave of slack up the rope to release the cam. It works instantly.
While the Ohm manages the weight, mastering proper belay technique is still the foundation. The device buys you friction, but your stance ensures the rope flows.
Final Thoughts
The “Rocket Effect” is a real danger when the percentage difference in weight is high. The Ohm fixes this by reducing force on the climber and adding “virtual weight” to the belayer.
The Ohm II is tough and great for the gym, while the new Ohmega is light and adjustable for the outdoors.
But remember, the gear only works if you use it right. Standing 1 meter back from the wall is the secret to making this device feel invisible.
Check the weight ratio between you and your partner today. If you are in the 10kg+ danger zone, try renting an Ohm at your local gym before your next lead climbing session. For more specs, check www.edelrid.com.
FAQ – Frequently Asked Questions
What is the minimum weight difference required to use an Ohm?
The German Alpine Club (DAV) recommends using the Ohm when the leader is at least 10kg (22lbs) heavier than the belayer. You can use it with a smaller difference, but the catch dynamics might feel a bit like a hard catch for the leader.
Can I use the Edelrid Ohm for trad climbing?
No, the Ohm is strictly designed for sport climbing with bolts. During a fall, the device pulls upward. This upward pull can lift removable gear like nuts or cams out of the rock, which could cause the anchor to fail. This is not for mountaineering safety or trad.
How do I handle device retrieval if the route is overhanging?
The safest way is to use a stick clip to grab it from the ground after the climber has cleaned the route. The climber can also unclip it while lowering, but the belayer must be ready for the braking resistance to suddenly disappear.
Why does the Ohm keep locking up when I try to clip?
You are likely standing too close to the wall or pulling slack too fast. Stand 1 meter back from the wall and use a smooth, steady motion when paying out slack. This creates a controlled catch environment and prevents short-clipping risk.
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