the cranks are the bike parts that take the most abuse
On a bicycle, the cranks connect the pedals to the chainring, so you can deliver power to the wheels. Besides the wheels, the cranks are the bike parts that take the most abuse. Every time you pedal, you bring your entire weight plus all of your strength down onto the pedals. Typically, cranks come in two different varieties: aluminum and carbon.
Each material has advantages and disadvantages that you want to consider. As a general rule of thumb, bike parts can only fit into two out of the three following categories: lightweight, durable, and inexpensive. If a part is lightweight and durable, then it will not be cheap. If it is inexpensive and durable, then it will not be lightweight, and so on. When it comes to choosing between aluminum and carbon, you have to decide which two of these are most important.
