16 December 2008

How sticky are your rock boots?

Is it possible to determine experimentally which company makes the best rock boots? Spadout.com [1] ran an article where they tested the coefficient of friction for various climbing shoe rubbers. The experimenter cut out pieces of boot rubber, put a small weight on top of the rubber and put the rubber on an inclined granite plane. The angle of the plane was then increased until sliding occurred; the sliding angle was used to give each rubber a ‘sticky rating’ – where a steeper angle required means stickier rubber.

The experimental setup used by spadout. Image from [1].

The 9 different rubbers showed a 6.5° range – which seems to suggest that there is not much difference between them (the results were later scaled to give more pronounced differences in the sticky rankings). Although in the realms of gnarly slab climbing a little extra friction might go a long way. However, rubber friction is not straightforward and there is more to rock boots than just the sticky factor.

The coefficeint of friction is not affected by normal force for most materials, but for rubber it can vary. Image from [2].

The friction coefficient for rubber can vary with normal force [2], in other words, unless you apply a force that is similar to the weight of a climber, the coefficient you obtain will not be representative. Of course, this will only disrupt the rankings if the different rubbers show different relationships between normal force and friction coefficient. Also, if each type of rubber has a different temperature at which it is designed to be optimal [3], testing the boots at the same temperature will mean that the results will be biased by how far you are from each boot’s preferred temperature.

Perhaps more important, climbing requires two seemingly contradictory properties; high stiffness for edging and soft sticky rubber for smearing on smooth slabs. The test may be indicative of smearing performance – but is that the most important aspect?

[1] http://www.spadout.com/r/climbing-rubber-test/

[2] M. Lindner, Experimental and analytical investigation of rubber friction, University of Hannover, Pdf here: http://fluid.ippt.gov.pl/ictam04/text/sessions/docs/SM2/12086/SM2_12086.pdf

[3] An interesting discussion of climbing friction: http://www.theshortspan.com/features/friction.htm

12 December 2008

Study found that having wet fingers does not reduce friction

An interesting study on how chalk and moisture affects a climber's grip was published in the Journal of Sports Sciences in 2001 [1]. The study found that applying water to the fingertips did not reduce friction. Their method involved pressing their fingers on a damp sponge. Shop clerks do this to give extra grip when they need to separate the layers of a plastic bag and people lick their fingers to make their fingers grip to the pages of a slippery magazine – does this mean that having wet hands increases grip for climbers? Any wet climbing experience will tell you otherwise. Climbers, weightlifters and gymnasts all use chalk to improve their grip, but with gymnasts they use it to allow their hands to slide more easily around the parallel poles. Clearly, the relationship between moisture, chalk and hand grip is not straightforward.

An extract from the study showing their experimental setup. From [1].

The authors attempted to tackle a very challenging subject for which it is difficult to create a meaningful experiment. How appropriate and how rigorous were their methods? “The fingers were pressed into a damp sponge … then pressed into a separate bowl of magnesium carbonate and the excess removed by tapping [the back of the hand]”. Is this representative of a real climbing scenario? How much chalk is applied? How much is removed by tapping? Is there anything in this method to prevent the following scenario? The fingers are wet from the sponge, and then they are dipped in just enough chalk to create a slimy paste on the finger tips.

They interpret their results as suggesting that “dry hands produce a higher coefficient of friction than when magnesium carbonate is applied to them. The effect would probably be amplified by the regular application of chalk, which desiccates the skin, reducing further the coefficient of friction.” And yet a few sentences later they state that “The manipulation of dampness did not yield any significant effect.” So dampness doesn’t affect friction, but if your hands are too dry it will reduce friction?

Furthermore, they conclude “All of this evidence strongly suggests that rock climbers should not use chalk when the fingers are already reasonably dry; if chalk is used to dry the hands, all traces of it should be removed before climing [sic]. As this is particularly difficult when rock climbing, an alternative method of drying the hands (e.g. using a towel) is preferable.” Their results show that having wet fingers does not affect friction – so why would they recommend drying your hands? They don’t believe their own results, if they have ever climbed before, this is not surprising.

[1] Journal of Sports Sciences, 2001, 19, 427-432. Pdf avaialable here:


5 December 2008

Camalot patent expired in 2005

Inventor Tony Christianson came up with the idea for a double axle cam and teamed up with Chouinard Equipment (now Black Diamond Equipment) to produce the Camalot [1]. He filed a patent (US 4,643,377) on 26th September 1985. This reached the end of its 20 year term on 26th September 2005. Protection in Europe was sought in Germany, France, Great Britain and Italy with an EPO (EP 0 223 964 B1) filing date of 25th September 1986 (one day before the 12 month Paris Convention time limit). The expiry of his European protection occurred 20 years from the EPO filing date – 25th September 2006.

Extract from Christianson’s Camalot patent (US 4,643,377)

Considering the popularity of the Camalot it is surprising that other manufacturers have not taken advantage of the now unprotected dual axle design. It has been 2-3 years since the protection ended and presumably the development of a Camalot copy would not take longer than 2-3 years. Either manufacturers are not aware that the patents have expired or have, for one reason or another, decided not to pursue the dual axle option.

An early Camalot prototype, image from [1].