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 Climbers love to debate about which rubber is the “stickiest”. The problem is who really wants to destroy their shoes to find out? 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. Raw stats. 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. Is Spadout biased? All the samples were purchased from retailers at full price (not from the manufactures). Spadout does not receive money from any of the manufactures. Spadout receives money from over three hundred retailers that sell many different types of climbing shoes (including all the shoes that we tested). Spadout's revenue depends on the total sales sent via our site. It is irrelevant which products are sold, therefore we can remain unbiased. Climbing Rubber Test
The test setup was designed and built by Steven Won, a physicist at CERN and an avid climber. Each sample was placed on the marked portion of the granite. The screw (seen below the granite slab) was rotated, slowly raising the angle of the granite slab until the rubber sample failed. The height of a fixed point on the slab was measured (from the base) to determine the angle of the slab.
Shoes from which the rubber samples were attained
Details
Physics behind the test
In this experiment, the normal force is being adjusted by changing the angle of the surface with respect to the ground. The advantage of this approach is that it eliminates possible systematic errors involving the weight or surface area of the rubber sample. Mathematically, the coefficient of friction works out to the tangent of the angle between the surface and the horizontal.
Steven Won is the Huang Fellow at Northwestern University's Department of Physics and Astronomy, and a member of the USCMS collaboration at CERN. He is also a climber. |
The quantity we are trying to measure is called the "coefficient of friction," and it is a simple way to quantify the stickiness between two surfaces (in this case, the rubber and the granite or climbing hold). It is defined as the ratio between the normal force (defined as the force compressing two parallel surfaces together) and the frictional force, and is unique to each pair of surfaces.
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