Learn Spanish (Spain): El coche es superrápido.

In Spanish, prefixes for extreme degree like super-, extra-, and re- are written directly joined to the base word. You should not use a space or a hyphen, so it is superrápido rather than super rápido or super-rápido.

Why does superrápido have a double 'rr' when the base word rápido only has one?

Whenever a prefix ending in a vowel attaches to a word starting with an 'r', that 'r' must be doubled to 'rr'. This spelling rule preserves the strong, rolling 'r' sound. If it were written superápido, the single 'r' between two vowels would be pronounced as a soft flap, changing the sound of the word.

If we were talking about multiple cars, would the prefix change?

The prefix super- never changes form, but the adjective it is attached to still needs to agree in gender and number with the noun. For multiple cars (los coches), you would say son superrápidos.

How does using super- compare to using muy or the suffix -ísimo?

Adding super- is incredibly common in colloquial, everyday speech in Spain to express an extreme degree. While muy rápido is standard and works in any context, and rapidísimo is also common but slightly more formal, superrápido gives a very natural, conversational feel.