Learn Spanish (Spain): En la ciudad, la bicicleta es tan práctica como el coche. - In the city, the bicycle is as practical as the car.

When comparing adjectives (like práctica, meaning practical), you always use tan. The formula for saying 'as [adjective] as' is tan + adjective + como. You only use tanto or tanta when you are talking about quantities of nouns (like 'as much money as').

Coche is masculine, so why is the adjective feminine (práctica)?

The adjective describes the primary subject of the sentence, which is la bicicleta (a feminine noun). Since the bicycle is the thing being described as practical, the adjective must match its gender, becoming práctica. The gender of the second item (el coche) doesn't change the adjective.

Does the word tan ever change to tana to match feminine nouns like bicicleta?

No, tan never changes its form. It is an adverb (meaning 'so' or 'as'), and adverbs don't have gender or plural forms in Spanish. Only the adjective (práctica) changes to match the noun.

Why do we use es instead of está here?

We use es (from the verb ser) because being practical is seen as an inherent characteristic or general fact about the bicycle in the city. If we were talking about a temporary state or location, we would use estar.