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Climbing Rubber Friction Test


Submitted by markanite on 2008-11-21

Rating: 12345   Go Login to rate this article.   Votes: 2 | Comments: 14 | Views: 7095

by Mark Silliman


Rockclimbing Article Image1_large
Climbing Shoes used in Test
Spadout.com

Methods

We measured the angle at which the rubber sample failed (slid) on both granite and a flat plastic hold. In both cases the range between the best and the worst rubber was less than 6.5 degrees.

What we tested

We tested all "popular climbing rubbers". This is defined by rubber featured on at least one climbing shoe that is sold by at least 5 online retailers.

How the tests were performed

There are nine popular climbing rubbers on the market today. We purchased one pair of shoes for each type of rubber. The soles were removed and 2x2 inch samples were cut. A weight was taped to the top of each sample. The samples were placed at the same starting location on a granite slab. The angle of the ramp was increased until the sample failed. The angle was measured.

The same process was repeated on a flat climbing hold. Twenty tests were done for each rubber type (10 for plastic, 10 for granite). Both the left and right shoe's rubber was tested to verify the test was consistent. We also did a “pull test” (using a spring scale and a 5 lbs weight) and received similar results.

Full Results

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14 Comments CommentAdd a Comment

 noercarr
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 2008-11-22
Im no Scientist, but the test piece of "granite", looks more like a piece of "slate", which surface texture is quite different.
 apeman_e
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 2008-11-22
I love the idea of testing rubber, and I am no scientist, but I have doubts. Maybe some rubbers are more effective when significantly weighted (15 oz is so small)? It seems to me like such a nearly weightless test would measure different properties than a heavily weighted shoe. Is there a difference? Are friction and holding power exactly the same? Maybe some rubbers are more effective when the rock is really forced deep into the rubbers, instead of the superficial, outer-layer-only skid test??

Love the test, keep up the good work!

e

Keep up the good work!
 apeman_e
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 2008-11-22
oops too much keep up the good work! what I tool i am...
 brachialis
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 2008-11-22
One non-trivial variable to account for is rubber temperature. We all know from experience that climbing rubber tends to heat up as you climb, and I would hypothesize that different climbing rubbers behave differently as temperature is varied, and that under uniform climbing conditions, a rubber's temperature increases at different rates for different rubbers.
 joeforte
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 2008-11-22
More tangential force (weight) would certainly effect the test. Rubber behaves the way it does because it conforms to irregular surfaces very well. More force would cause the rubber to deform more, and more effectively match the surface texture. I would LOVE to see this test done with more weight on the rubber sample!
 jermanimal
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 2008-11-23
I think joeforte and apeman_e have a very valid point, rubbers properties to conform to the surface may not be tested here at all without using more weight. The 15oz over a 2x2 area may have far too much reliance on the finished surface of the rubber becoming a factor.
 jermanimal
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 2008-11-23
100 lbs over 1x1 would have been better. And, yes this contraption would have been very easy to build.
 bachar
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 2008-11-24
Useless test. Formula 1 tire rubber beats all these rubbers in this test but sucks on the rock.
 madrock
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 2008-11-25
1 out of 5 stars I will pay to have an outside independent lab do testing to an established ASTM standard if the site really wants to publish useful information.

joeforte is 100% correct. The ability for the rubber to conform to the surface under a load in primarily important and yet totally ignored in this test. Why with so many accurate machines and standardized tests that more correctly determine the friction of climbing rubbers did the website come up with such a ridiculous, unrealistic and contrived test standard? More importantly why would rockclimbing.com put it forward as if presenting factual and useful information?

I will try to cover the multiple other problems with this test through a direct PM to the tester .

Joe
 dudemanbu
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 2008-12-03
kneads moar wait.

(needs more weight.)
 drfelatio
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 2008-12-15
A 15oz. weight on a 4 sq in piece of rubber would exert less than 0.25psi of pressure. I wonder if I'm applying more than that on my keyboard as I type this comment?
 pbjosh
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 2009-01-07
Useless test...
 markmello
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 2010-10-13
formula one rubber, like all race tire rubber, only does a great job once it is warmed up. If you put in on a rock climing shoe, it will not reach the same temp, unless you plan on climbing at 190mph.
so don't get your nomex nascar panties bunched up. Secondly, if a peice of rubber can do well with 15 oz, more direct pressure will only make it stick better. Although if you add more weight, you have to consider the weights center of gravity, so don't go thinking a bigger weight will make much of a difference. Think about a gecko as well; it weighs much less than 15oz, yet can hang upside down. If it had a backpack with a 5 pound weight, that's not gonna give any more sticking power. Good test in theory, but what you should be worried about, was that you'll never know how biased the tester was before he started, and if the results are real.
 Chema23
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 2012-04-21
Markmello,

Rubber has many properties that contribute to friction: adhesion, abrasion resistance, and shearing resistance to name a few. Of course there are factors such as temperature, shape, and magnitude and duration of pressure that will affect climbing shoe performance as well, but for now I'll stick to the properties mentioned which are specific to a particular type of rubber.

Adhesion is how sticky or tacky the rubber feels, this is good for showing off your shoes by hanging one off the edge of another (if you've never done this it's really cool, take two brand new shoes with super clean edges, warm up the toe a bit by rubbing them together or against your hand, then press the toes together really hard and let go of one shoe, it should hang off the other for a moment). Apart from that, and collecting chalk and dust, that's about all adhesion is good for, oh and probably holding 15oz. on an incline. See, adhesion is useful when not much force is involved, and it's usually what people think of when they think of friction. I mean, chewing gum is really sticky, but wouldn't make good climbing rubber.

Abrasion resistance, now we're talking. This is the rubbers ability to not smear off its outer layers. Gum might be able to hold a piece of paper upside down, but put gum on the toe of your climbing shoe and you better believe it will decrease your shoes performance. This is like stickiness for grown ups, you notice it when there's a lot more pressure being applied. I am over-simplifying it though, because steel is highly abrasion resistent, but it won't make you stick to the wall better, and than's because it's too hard. The rubber needs to be soft enough to conform to the texture of the wall under normal climbing loads (anywhere from a couple to a couple hundred pounds, depending on how hard you're pushing of course), but hard enough to not abrade away when the loads get toward the higher end.

Shearing is when big chunks are taken out, and this is why edges taper in. If climbing shoe edges flared out (so that it would be easier to get your edge on that tiny crystal), the flared edge would just tear off. You've probably noticed that you get little ribbons of rubber running along the edge of new shoes after just starting to climb (I always tear them off compulsively), that is shearing at work. You can think of shearing as the big brother to abrasion. Just as adhesiveness deals with really small amounts of weight and rubber, and abrasion deals with larger amounts, shearing deals with even larger amounts.

ok i'm tired of writing, I hope that made sense, and seemed relevant.

Cheers,
Chema

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