Janta este deteriorată.

Because Romanian usually puts the definite article at the end of the noun.

• jantă = a rim
• janta = the rim

So janta already includes the idea of the.

No. The basic form is jantă.

This sentence uses the definite singular form:

• jantă = rim
• janta = the rim

A native English speaker often expects a separate word for the, but in Romanian it is often attached to the noun.

Both are possible.

• este = the full form of is
• e = a shorter, very common form of is

So both of these work:

• Janta este deteriorată.
• Janta e deteriorată.

The version with este may sound a little more neutral or formal, while e is very common in everyday speech.

Because it has to agree with janta, which is feminine singular.

In Romanian, adjectives change form to match the noun’s:

• gender
• number
• sometimes definiteness/context

Here:

• janta = feminine singular
• deteriorată = feminine singular form of the adjective

Compare:

• janta deteriorată = the damaged rim
• cauciucul deteriorat = the damaged tire
  (cauciucul is masculine singular, so the adjective becomes deteriorat)

Not exactly. Jantă specifically means the rim of a wheel.

Useful distinctions:

• jantă = rim
• anvelopă / cauciuc = tire
• roată = wheel

So janta este deteriorată means the rim is damaged, not necessarily the whole wheel or the tire.

Normally, no in a sentence like this.

Romanian usually keeps the verb to be in the present tense:

• Janta este deteriorată.
• Janta e deteriorată.

Leaving it out would sound incomplete in standard Romanian.

A simple pronunciation guide is:

Janta este deteriorată
ZHAN-ta YES-te de-te-rio-RA-tuh

A few notes:

• j sounds like the s in measure: /ʒ/
• e in este is pronounced clearly
• ă is the Romanian central vowel, a short neutral sound, somewhat like the a in sofa

The stress in deteriorată falls on ra:
de-te-rio-RA-tă

There are other options, depending on nuance.

• deteriorată = deteriorated, damaged, worn down
• avariată = damaged, especially by impact or accident
• stricată = broken, not working properly

So:

• Janta este deteriorată. suggests the rim is in bad condition.
• Janta este avariată. suggests it has been damaged, perhaps by a hit or accident.

Deteriorată is a perfectly natural choice, especially if the condition has worsened over time or is generally poor.

Yes, it is completely normal.

The pattern is:

noun + este/e + adjective

So:

• Janta este deteriorată.

This is the standard way to say The rim is damaged.

You could also see the adjective used before the noun in a larger phrase, but in a basic statement like this, the given order is the most straightforward.