Yes. The rim, for instance, is made of yet smaller parts.
Part of the skill of object oriented programming is in designing the right software objects to match the real world objects of the problem, and in determining the right level of detail. Modeling the bicycle in terms of its components would likely be useful. But you would not want to analyze the bicycle until you were looking at atoms.
A good flight simulator program (for example) is realistic because its airplane objects are built up from many small objects. A crude simulation uses fewer objects.
Say that you wanted to model a pine tree. Perhaps all you need for the situation is a simple model (as pictured). Perhaps this is for a computer game and you don't need much detail.
What smaller objects does this simple tree model consist of?