Friction: The Truth Behind Perfect Climbing Conditions
“It’s greasy,” we say on hot days when the holds feel like soap. But while it’s easy to blame the stone, the fault actually lies in our own physiology. On those smarmy days, we lack friction. To find ideal conditions and increase our chances of sending, we first need to understand how we stick to the rock.
A study published in 2012 in Sports Biomechanics found that using chalk increased friction on limestone by 18 percent and by more than 21 percent on sandstone. However, research has also found highly dry skin to be nearly as slippery as wet skin. Because the rigidity means it can’t mold to those microscopic edges.
Ultimately, keeping skin soft and supple will increase friction when other factors, like temperature, can’t be controlled for. A 1981 paper in the Journal of Cosmetic Science found that moisturizers gave hands better friction once the moisturizer has been absorbed, since the increased skin malleability allowed more surface-area contact. Thus it may help to keep hands moisturized between climbing sessions, with lotion or post-climb balm.
On a microscopic level, friction works when two objects rub against each other. This is quantified by a coefficient. It measures the force needed to slide one surface over another divided by the pressure between the two surfaces. In the case of climbing, it’s the rock’s rugosities—the tiny edges and wrinkles—catching our hands that create friction.
Slippery surfaces, like polished marble, have few edges to catch. Sandstone, on the other hand, is comprised of millions of tiny compressed granules providing a multitude of microscopic edges—and thus greater friction. For reference, the coefficient between a hand and limestone is around 0.64. Whereas on sandstone it’s approximately a grippier 0.74.