In reply to John Kelly:
> Thanks - cam angle not 'significant' effect (great), complex geometry of unit leads to odd modes of failure - kind of makes sense' - love C4
No I don't think I quite said that. All things being equal, if you have a rough, grippy surface where minor deformation of the lobe surface creates a mechanical interference between the grain structure of the rock and the metal, then camming angle will play a much smaller role.
On smooth rocks, the friction must be improved or a mechanical interference created by nestling the lobes into rugosities in the crack. Here it will have a far greater effect, as will a softer lobe material, and where cams like the Totem totems will come into full effect, especially in more marginal placements. Can C4's pull out in this sort of rock? Absolutely so you need to modify the way you place them to ensure they don't. I climb mostly on limestone or Dolomite, both smooth fine grained rocks and I will tend to try to place cams in constricted pockets where the friction becomes less relevant.
On soft rocks, which by and large are rough and grippy like sand stone or granite, then rock puverisation will play a bigger factor with crushed rock essentially becoming a lubricant and leading to pullout. So in this case spreading the stress transmitted to the rock to a larger area by using a wider cam lobe will improve holding power.
So this is why when I was doing the work for WC on their lobes we went for as wide as we could manage, in a medium soft metal which will still be strong enough not to buckle (especially as the lobes get bigger this becomes a problem) and with a conservative middle of the road cam angle. It's interesting to note that as DMM redeveloped their dragon lobes they came up with nearly exactly the same design, including strengthening ribs in the same places. This was all done totally independently, so we're pretty sure we've got it about as right as we can get it in system which will by its nature be a series of compromises...