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basilisk
May 12, 2009, 12:39 AM
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Preface: I'm posting this in the lab because I'm hoping some math folks will step in and show me what-for
I'm addressing this topic specifically using shoes, and looking at how they'll be most functional. When it comes to slab climbing I often hear people saying things like "Get as much of your shoe on the rock as possible" or at the least the whole front of your foot- you catch my drift. I understand the logic here is that more weight on more surface area = more friction = better stick, but I'm not convinced. Crampons work with the opposite idea, the logic there is: more weight on smaller area = more friction = better stick. This idea I at least know is proven to work.
So to bring that idea back to slab climbing, by using more of our foot, are we in fact spreading out our weight and getting less stick?
I'm sure some people can thrown down information on friction coefficients and how ice is way different from rock because it gives more. I'd love to see some complicated shit I can't possibly understand, but please dumb it down for me too
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hafilax
May 12, 2009, 1:04 AM
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The physics of friction is actually extremely complex and doesn't just depend on the force but also on the area and surface roughness. In the case of rubber on rock and specifically slab climbing it's more about the rubber forming around the rock crystals and hooking up. The more things you can get the rubber to hook up on the more likely you are to stay on. If you working with a single small feature then if you smear on it, even if a part slips off there is a good chance that the rubber will hook up again.
Crampons don't really work with friction at all. They make holes in the ice and you really can't draw analogies between friction on rock and using crampons.
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rgold
May 12, 2009, 1:11 AM
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We all know intuitively that the gross oversimplifications behind elementary coefficient of friction approaches (such as the fact that surface contact area is irrelevant and only normal force matters) completely inadequate for explaining the sense of "friction" as climbers experience it. (This has not kept Spadout from publishing statistically incompetent and scientifically deficient friction experiments, however.)
Although about racing-car tires, the following account nonetheless addresses most of the issues relevant to climbing soles on rock.
http://insideracingtechnology.com/tirebkexerpt1.htm
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ryanb
May 12, 2009, 2:10 AM
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I'm a bit of a math person and more importantly, i've been on my share of slabs.
Following the interpretation of friction taught in undergraduate physics you should try and stand on the best (and most usefully oriented) part of the hold no matter how small....if friction is independent of area maximizing the normal force and coefficient of friction is all that matters.
This can be a really good foot work drill, taken to its logical conclusion it often means attempting to edge every foot hold even if it means front pointing tiny crystals with the pointy toes of a pair of Miuras.
(Incidentally i wore out the toes of several pairs of shoes while taking undergraduate physics)
Do this long enough and you realize that the limiting factor is how quickly the edge of the rubber deforms and slumps/melts off the hold... this varies from shoe to shoe and rubber to rubber and with conditions. At some point the edges just don't work and you have to start using the rest of the foot either to spread the force out and reduce edge roll (smearing, smeding) or to manipulate the direction of the normal vector and utilize a more favorable aspect of the hold (heel hooking, foot jamming, rand jamming (really great in pockets and corners on non crack climbs), toe scumming).
So climb more.
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adatesman
May 12, 2009, 3:36 AM
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ryanb
May 12, 2009, 4:25 AM
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rgold wrote: ryanb wrote: Following the interpretation of friction taught in undergraduate physics you should try and stand on the best (and most usefully oriented) part of the hold no matter how small....if friction is independent of area maximizing the normal force and coefficient of friction is all that matters. This may or may not be good advice, but as I just mentioned, the undergraduate physics description of friction is simply inadequate as a characterization of rubber on rock. Read the link!
I think that the F_f = u F_n idea of friction is a more then significant model when it comes to developing good footwork.
I read the link when bachar posted it on supertopo. It is interesting but, in my opinion, does not apply directly to climbing shoes for a few reasons:
1) It describes Fdef and Fwear in terms of "sliding speed" which is minimal in climbing. Off normal force would be interesting but sliding speed is not.
2) It clearly states that 2 of the phenomena it describes are only play a significant role in wet conditions and that adhesion is the major contributer in dry conditions.
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3) Deformation of rubber seems to hurt shoe performance on small edges and holds, ideas developed for racing tires do not capture this at all.
If i take the ideas from that paper and eliminate the ones that depend on sliding speed I get a model where F_f depends on F_n. Since I am not actually measuring anything while climbing and don't wish to over think things  , I am more than happy with a linear approximation and we are back at something like F_f = u F_n.
More complicated ideas may be needed if you are actually developing rubber for climbing but i suggest focusing on static performance unlike the racing industry.
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spoon
May 12, 2009, 4:40 AM
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In reply to: I'm surprised they didn't mention siping though... From what I've read its quite effective in increasing traction in racing slicks and I'm surprised it hasn't made its way onto climbing shoes yet.
Interesting that you should mention this, as I distinctly remember my father, who climbed in the 60's and maybe 70's, saying that he and his friends would cut a crisscross pattern into the bottom of their climbing shoes with razor blades to increase friction. I'll have to ask him about it.
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hafilax
May 12, 2009, 7:28 PM
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The normal force is the same no matter what the surface area is so edging and smearing are no different in that regard. Undergraduate physics friction labs never work ideally and the whole F=mu N is more of an exception than a rule, especially for rubber.
Wear friction and deformation are incredibly important in slab climbing. When you are standing on that small feature the rubber must deform to take the shape. This can go beyond elastic deformation.
The paper speaks of velocities but they don't have to be high to be significant. I have stood on marginal holds and could feel the clock ticking as my foot slowly crept off the hold. I can also tell you that after a day of slab climbing, even without falls, that my shoes show definite signs of wear.
I strip routes at the gym and the jugs are always filled with little beads of rubber like those described in the article. Gym footholds are huge and even they cause wear on the shoes showing signs that wear friction is important even there.
What it all really boils down to is trying smearing and edging in as many scenarios as possible and figuring out which works best for the rock you are climbing.
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jkd159
May 15, 2009, 7:31 PM
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adatesman wrote: I'm surprised they didn't mention siping though...
Last year I played with siping an old pair of shoes. I found it led to rapid sole failure. Maybe I made poor choices for cut spacing and/or depth.
Love the traction it gives my snow tires!
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hafilax
May 15, 2009, 8:32 PM
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I thought siping was more for traction on wet or icy surfaces. The slits allow water to go into the tire instead of getting displaced. The wiki claims that an unsiped tire performs best in dry conditions and that a siped tire will be "squirmy".
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krusher4
May 15, 2009, 8:42 PM
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can't we all just go climbing now?
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krusher4
May 15, 2009, 9:18 PM
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sspssp wrote: krusher4 wrote: can't we all just go climbing now? No, I'm stuck at work. 
understood LOL
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adatesman
May 17, 2009, 10:46 PM
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grampacharlie
May 17, 2009, 10:54 PM
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From what I understand, it does improve handling and performance, but it does reduce the longevity of the surface being siped.
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