The term 'bicycle wheel' can be broken down into two parts: TIRE and wheel. The solution for the term 'TIRE' is a four-letter word, which is 'TIRE'. A TIRE is an essential part of a bicycle wheel, as it provides traction and absorbs shock when riding on different surfaces. It also helps to keep the wheel in place and prevent it from slipping off the axle. The wheel itself is the circular metal structure that holds the TIRE in place and allows the bike to move forward. Together, the TIRE and wheel make up the bicycle wheel, which is an important component of any bicycle.