Necessity is the mother of invention, in both the natural and man-made world. To understand the reason behind bamboo's strength, and the strength of our bamboo bikes, start by asking the question why. Why does bamboo need to be so strong? Trees don't need to be that strong, and they appear mightier than humble bamboo.
The answer to the questions lies within bamboo's unique shape. Very basic engineering principles teach us that the taller an object gets, the more weight is exerted on it's base. Even more force is applied to the base when the top sways slightly and the base becomes a fulcrum, resulting in exponentially increased pressures from the leverage effect.
For example, say you want to stack three people high. Cheerleaders do it using a pyramid. Three on the bottom, two in the middle, one on top. This design spreads the force more evenly and drastically reduces the amount of leveraged force from swaying. Instead of carrying the weight of two people, the bottom end people carry only the weight of only .75 of a person, and the bottom middle carries 1.5 people.
Trees do the same thing. They don't always look it, but they are much thicker at the base than they are on top. Take away their branches and leaves and it's easy to see: tree trunks are shaped like cones.
Bamboo, on the other hand, is shaped like a rod. Its diameter is the same at the top as it is on the bottom. Most bamboo species range from 15 - 39 feet tall. Imagine the amount of force. That's like stacking 5 people on top of each others' shoulders, a feat accomplished by only the most talented and rock hard professional acrobats. Some of the tallest bamboo averages 98 feet tall. Can we stack 20 people on each others shoulders? Kids, don't try this at home.
Nature, in its infinite wisdom, created a material that could withstand tremendous pressures out of necessity. Bamboo's micro-structure, and resulting strength, make it the perfect material for bikes and hundreds of other uses. Bamboo bikes are strong and beautiful, but check out these amazing pics of bamboo used to build skyscrapers!