Cams - Technical Question

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Cams - Technical Question

Post by Leebo » Sat Mar 10, 2012 1:20 pm

Maybe someone can give me some insight into what ultimately determines the strength of a cam.

From what I can see, throughout a specific model size range, all the cam shafts and axels are the same diameter yet the kN ratings vary - bigger the cam, bigger the kN rating. So is it the size of the cam lobe that determines the strength?

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Re: Cams - Technical Question

Post by Oakley » Sun Mar 11, 2012 8:44 am

The strength of the weakest link determines KN rating.

Not all shafts are similar diameter, but I think the most important factor is the size of the axle that the cams rotates around and where the cable joins with the cam body.

PS - I found a report of someone that did a thesis report on a cam lobe, it turns out that the lobe itself only failed at 54.15KN.(BD C4 #3)

(If anyone want the report PM me your email address, Its quite a good explanation for how strong cams are)

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Re: Cams - Technical Question

Post by Oakley » Sun Mar 11, 2012 8:48 am

Ahhh, found the internet link, so download it yourselves.... :afro: ... 8eJ7_J5B-Q

Warren G
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Re: Cams - Technical Question

Post by Warren G » Mon Mar 12, 2012 12:35 pm

On BD Camelots the weakest point is the webbing, generally. This sort of relates to another active thread, and my only comment here again would be to echo another comment there: a 14kn fall is a HUGE one- that's you feeling 1.4 tons on your harness: imagine the bruising etc associated with that? I bet the reason they chose 22kn as the industry standard is due to breaking backs, femurs, rupturing arteries, kidney damage etc to a level beyond what the average human could survive. 22kn generated out of a 0.8kn mass- you- means a G force of 27.5!

The other general comment I would like to make regards uses of smaller Cams or even nuts: the super small units are designed for aiding, not lead falls, both the Wild Country Zeros and the BD C3's have low breaking forces*, in their smaller sizes. Some micro nuts have 2kn breaking force- 200kgs of static force, if it is an ideal placement and the units in perfect condition. lets harp on this ideal placement one moment: the gear is lab tested many times before they designate a breaking force, using an ideal placement situation, uniform surfaces set at an ideal distance apart. How can you reasonably ask a 2kn nut to take a 3m fall of the 80kg you? Aiding device, not leading device.

* I say "breaking force" rather than Safe Working Load, as recreational climbing gear is not rated in that way, amazingly. If you put 23 kn on something rated for 22kn it WILL fail, or it would say 23kn.
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Nic Le Maitre
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Re: Cams - Technical Question

Post by Nic Le Maitre » Mon Mar 12, 2012 12:53 pm


It is some time since I last checked up on this but as far as I can remember the European Fall Arrest Standard says that falls with arrest forces less than 6kN will not result in injury and up to 12kN is survivable with severe injuries. More than 12kN is not survivable. With all the absorbency built into climbing gear as well as the friction through knots and over edges and gear you will never experience forces this large unless you fall on to a static system (like a sling) or cock up a via ferrata really badly.
Happy climbing

Andy Davies
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Re: Cams - Technical Question

Post by Andy Davies » Mon Mar 12, 2012 8:44 pm

Weakest link is the dude who placed it :shock:

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Re: Cams - Technical Question

Post by Franz » Tue Mar 13, 2012 8:22 am

Now with Andy I agree!
(same goes for bolting)

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Re: Cams - Technical Question

Post by Scott » Tue Mar 13, 2012 10:05 am

Andy Davies wrote:Weakest link is the dude who placed it :shock:

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