Learn Portuguese (Portugal): A roda da bicicleta é pequena.

In Portuguese, you usually include the definite article (a, o, as, os) when talking about a specific thing. Here, it is not just any bicycle, but a specific one. So, we combine the preposition de (of) with the feminine article a (the) to make da (of the).

Why is the verb é used instead of está?

We use é, from the verb ser (to be), to describe permanent or basic characteristics. Since being small is a fixed physical trait of this wheel, we use ser. If we used está (from estar), it would sound like the wheel is only temporarily small!

Pequena means small, but why is it feminine? Is it matching roda or bicicleta?

It is matching roda (wheel), which is the main subject of the sentence. Because a roda is a feminine noun, the adjective must also be in its feminine form, pequena.

If I wanted to say 'The bicycle's wheels are small', how would this sentence change?