Bamboo is a composite material, meaning it is made of multiple substances whose properties combine to create something with unique traits.
The two materials that make up bamboo are lignin and vascular bundles. The lignin is a fleshy material that insulates and contains the vascular bundles, which carry water and nutrients. These bundles also become extremely stiff and strong after curing.
As a result of its dense and fibrous vascular bundles, bamboo is incredibly stiff. It is also excellent at damping high-frequency vibration because of the fleshy lignin. An extremely stiff material which absorbs harshness…sounds like a brilliant material for a bike frame!
Things get even more interesting. Bamboo’s vascular bundles are entirely unidirectional, along the length of the tube (longitudinal). The fibers have a Young’s Modulus (stiffness against bending) similar to carbon fiber, but are not as stiff in torsion (rotational torque).
When out of the saddle sprinting or climbing steep grades, the entire frame is put in a lateral-bending mode and the bamboo excels at resisting this bending, and thus transfers maximum power to the road.
When cornering, descending, or riding in very rough terrain, the front half of the frame is under torsion, and the bamboo allows for additional compliance in these circumstances. As a result of this torsional forgiveness in the material, cornering is a treat. The bike feels stable and secure, providing greater confidence in treacherous conditions and at high speeds.
Bamboo’s final unique property is a rising rate of stiffness, as measured by its Young’s Modulus. The “snap” that bamboo is famous for comes from this very trait, and is why a bamboo bike frame feels lively. There is an initial amount of give, where a smaller load application results in deformation of the material. But as the load increases, the deformation increases at a slower rate. This progressive stiffness gives the rider an initial compliance found in plusher bikes, but stiffens up quickly like an all-out maximum stiffness race bike.
With a stiff, lively ride that is also supple and compliant, bamboo allows the rider to have their cake and eat it too.