Bieżnik jest dobry, a układ kierowniczy i klakson są sprawne.

In this sentence, bieżnik means the tire tread—the patterned outer part of a tire that touches the road.

A useful note: bieżnik can mean other things in other contexts, but in car-related language it usually means tread.

They can both be translated as and, but they are used differently.

• i simply joins words or phrases: układ kierowniczy i klakson = the steering system and the horn
• a joins two clauses and often suggests a slight contrast, shift, or comparison: Bieżnik jest dobry, a... = The tread is good, and/as for...

So here:

• a connects the first statement to the second
• i connects the two things inside the second subject

Because the subject changes from singular to plural.

• bieżnik is singular, so you use jest = is
• układ kierowniczy i klakson is a compound subject with two things, so it is plural, and you use są = are

So:

• Bieżnik jest dobry = The tread is good
• Układ kierowniczy i klakson są sprawne = The steering system and the horn are functional

Because dobry must agree with bieżnik in gender, number, and case.

Bieżnik is:

• masculine
• singular
• nominative

So the adjective also has to be masculine singular nominative:

• dobry

That is why you get bieżnik jest dobry, not dobra or dobre.

Because układ kierowniczy i klakson is a plural subject, and in Polish plural adjectives must agree with the type of plural.

Here both nouns are:

• masculine
• but not masculine personal (they are things, not people)

For non-masculine-personal plural, the adjective form is sprawne.

So:

• sprawni would be used for a group of men or mixed people
• sprawne is used for things, animals, or non-masculine-personal groups

That is why:

• układ kierowniczy i klakson są sprawne

They are similar, but not identical.

• dobry means good
• sprawny means working properly, functional, in good working order

In technical contexts, sprawny is very common for parts, systems, devices, and mechanisms.

So in this sentence:

• bieżnik jest dobry suggests the tread is in good condition
• układ kierowniczy i klakson są sprawne means the steering system and horn work properly

The nouns are in the nominative case, because they are the subjects of the sentence.

• bieżnik — nominative singular
• układ kierowniczy — nominative singular
• klakson — nominative singular

The adjectives dobry and sprawne are also in nominative forms here, because they are predicate adjectives used with być (to be).

Układ kierowniczy is a noun phrase made of:

• układ = system
• kierowniczy = steering

The adjective kierowniczy agrees with układ:

• masculine
• singular
• nominative

So układ kierowniczy literally means steering system.

This is a very common Polish pattern: noun + adjective, where the adjective usually comes after the noun.

Because Polish has no articles.

English needs words like:

• a
• an
• the

Polish usually does not use anything equivalent. The meaning is understood from context.

So:

• bieżnik can mean a tread or the tread
• klakson can mean a horn or the horn

In a sentence like this, the context makes it clear that we are talking about specific car parts.

In Polish, a comma is normally used before a when it connects two clauses.

So:

• Bieżnik jest dobry, a układ kierowniczy i klakson są sprawne.

This is standard Polish punctuation.

A native English speaker may notice that this is actually similar to English, where a comma often appears before a coordinating conjunction joining two full clauses.

Yes, Polish word order is more flexible than English, because endings carry a lot of grammatical information.

The given sentence has a neutral, natural word order:

• Bieżnik jest dobry, a układ kierowniczy i klakson są sprawne.

You could change the order for emphasis, for example:

• Dobry jest bieżnik, a sprawne są układ kierowniczy i klakson.

That is grammatically possible, but it sounds more marked or emphatic. For a learner, the original version is the best neutral model.

A rough English-friendly guide:

• Bieżnik ≈ BYEZH-neek
• układ ≈ OO-kwat
  (the ł sounds like English w)
• kierowniczy ≈ kyeh-rov-NEE-chih
• klakson ≈ KLAK-son
• sprawne ≈ SPRAV-neh

A few useful sound notes:

• ż sounds like the s in measure
• ł sounds like w
• rz often sounds like ż
• ie often gives a ye-like sound after a consonant

So bieżnik and kierowniczy are often the hardest words here for English speakers.