Why are climbing ropes rated so low?

JonasMRwrote: So, the real question is why is protection rated so low, right? If my old rope now limits forces of a 1.77 factor fall to 9kn, and we use Petzl's 2/3s number for the pulley reduction due to friction, we get 5/3 * 9kN = 15kN on that top piece. But my nice new 1" cam is rated to 14kN.

Of course we are floppy bags of mostly water, and the belayer moves, and 14kN is the mean failure minus 3 sigma. But what if I can only get a .3 cam (rated 8kn) for my jesus nut? The actual protection part of the system sure doesn't seem over-designed. It's always seemed scarily close to catastrophic failure if we are only surviving because of our squishiness. But maybe I'm doing some arithmetic wrong?

The top anchor sees 3/3 of the force. 2/3 from the climber [9kn] + 1/3 from the belayer [4.5kn] = 13.5kn.

rocknice2wrote:

The top anchor sees 3/3 of the force. 2/3 from the climber [9kn] + 1/3 from the belayer [4.5kn] = 13.5kn.

I don't believe this is correct. By basic Newtonian physics, if the climber experiences (up to) 9 kN, the top piece experiences that same load. 

Add in 2/3 of that effect on the belayer side and you get total of 15 kN.

Gunkiemikewrote:

I don't believe this is correct. By basic Newtonian physics, if the climber experiences (up to) 9 kN, the top piece experiences that same load. 

Add in 2/3 of that effect on the belayer side and you get total of 15 kN.

Scenario 1 - climber is falling on a fixed piece rope is tied to it, force on the climber is the same as on the piece
Scenario 2 - climber is falling on a fixed piece, but the rope is running through frictionless pulley, force on the piece is 2x force on the climber. ( N's 3 law - forces on both side of the pulley are equal, hence the force on the piece is force on the climber + force on the other side of the pulley, which is the same)

Scenario 3 - climber is falling on a fixed piece, but the rope is running through a carabiner. This one is a bit trickier, one can perform scientific calculations fueled by hand waving and guestimation. But, the answer is going to be between 1 and 2, probably closer to 1.5 of climber force. IIRC - there are actual tests done, can be found on google.

JonasMRwrote: So, the real question is why is protection rated so low, right? If my old rope now limits forces of a 1.77 factor fall to 9kn, and we use Petzl's 2/3s number for the pulley reduction due to friction, we get 5/3 * 9kN = 15kN on that top piece. But my nice new 1" cam is rated to 14kN.

Of course we are floppy bags of mostly water, and the belayer moves, and 14kN is the mean failure minus 3 sigma. But what if I can only get a .3 cam (rated 8kn) for my jesus nut? The actual protection part of the system sure doesn't seem over-designed. It's always seemed scarily close to catastrophic failure if we are only surviving because of our squishiness. But maybe I'm doing some arithmetic wrong?

The simple reason is that higher ratings would eliminate the ability to build any small gear (nuts and cams) and would make larger gear much heavier. (Wanna carry a whole rack of steel carabiners?)  The systems work fine for a broad spectrum of outcomes and only approach marginal at rarely-realized upper extremes.  Climbers are comfortable living with the thin margins for very high FF falls as a trade for much lighter gear for everyday use.

JonasMRwrote: So, the real question is why is protection rated so low, right? If my old rope now limits forces of a 1.77 factor fall to 9kn, and we use Petzl's 2/3s number for the pulley reduction due to friction, we get 5/3 * 9kN = 15kN on that top piece. But my nice new 1" cam is rated to 14kN.

I agre with what rgold said.

Plus if you manage to fall on a piece & generate 14 kn... You may already have a broken pelvis or something. That and at that force, I'm not even sure all rocks will hold. I'd be curious to see what this would do to, say, Red Rocks sandstone.... 

Pepe LePoseurwrote: 
The rating on gear is the max it can get

important to remember this is under IDEAL circumstances...

Gunkiemikewrote:

I don't believe this is correct. By basic Newtonian physics, if the climber experiences (up to) 9 kN, the top piece experiences that same load. 

Add in 2/3 of that effect on the belayer side and you get total of 15 kN.

Yeah your right.