Ayakkabı dar olunca ayaklarım şişiyor.

Olunca comes from olmak (to be / to become) plus the ending -ınca / -ince.

In this sentence, it means something like:

• when
• once
• sometimes whenever
• and depending on context, even because / since

So Ayakkabı dar olunca is literally something like when the shoe becomes/is tight.

In natural English here, it is best understood as:

• When the shoes are tight, my feet swell.

Because dar is an adjective, meaning tight / narrow, and the ending -ınca attaches to verbs, not directly to adjectives.

So Turkish uses:

• dar olmak = to be tight

Then:

• dar olunca = when it is tight

Compare:

• Ayakkabı dar. = The shoe is tight.
• Ayakkabı dar olunca... = When the shoe is tight...

So olmak is helping turn the adjective phrase into something that can take the -ınca ending.

This is a very common thing learners notice.

In Turkish, a singular noun is often used in a generic or collective way, especially when the exact number is not the main point.

So ayakkabı here can feel like:

• shoe / footwear / shoes in general

Even though English usually says shoes, Turkish can naturally say ayakkabı.

More explicit alternatives are also possible:

• Ayakkabılar dar olunca ayaklarım şişiyor.
• Ayakkabılarım dar olunca ayaklarım şişiyor.

These sound more specifically like when my shoes are tight.

So the original sentence is natural; it just uses a more general noun.

Turkish often leaves possession unstated if it is already obvious from context.

Here, ayaklarım means my feet, so it is easy to understand that the speaker is talking about their own shoes.

That is why ayakkabı can stay unmarked.

Possible versions:

• Ayakkabı dar olunca ayaklarım şişiyor.
  More general: When shoes are tight, my feet swell.
• Ayakkabılarım dar olunca ayaklarım şişiyor.
  More explicit: When my shoes are tight, my feet swell.

So the original sentence is not wrong or incomplete; Turkish just does not always state possession as directly as English does.

Ayaklarım breaks down like this:

• ayak = foot
• -lar = plural marker = feet
• -ım = my

So:

• ayaklarım = my feet

This is a very useful pattern in Turkish:

• el = hand

• ellerim = my hands

• göz = eye

• gözlerim = my eyes

• ayak = foot
• ayaklarım = my feet

Both are possible, but they feel a little different.

• şişiyor = present continuous form, but in Turkish this can also describe a repeated real-life situation
• şişer = aorist/simple present, often more general, habitual, or factual

So:

• Ayakkabı dar olunca ayaklarım şişiyor.
  Feels like when this happens, my feet swell / my feet end up swelling
• Ayakkabı dar olunca ayaklarım şişer.
  Feels a bit more like a general rule

In everyday speech, şişiyor sounds very natural here.

Because in Turkish, verbs often stay in 3rd person singular when the subject is an explicit plural noun, especially a non-human one.

Here the subject is:

• ayaklarım = my feet

Even though it is plural, şişiyor is normal.

So Turkish commonly says:

• Ayaklarım şişiyor. = My feet swell.

Using a plural verb like şişiyorlar would sound unnatural here.

A good rule of thumb:

• With explicit plural noun subjects, Turkish often does not mark plural on the verb.
• This is especially true with non-human subjects.

It can mean both, depending on context.

Basic meaning:

• dar = narrow

But with clothing, shoes, or anything that fits the body, it often means:

• tight
• too tight

So in this sentence:

• Ayakkabı dar means The shoe is tight or The shoes are tight

That is the most natural meaning here.

Yes, sometimes -ınca / -ince can have a causal feeling, like:

• when
• since
• because

In this sentence, the idea is:

• When the shoes are tight, my feet swell
• and also implicitly because the shoes are tight, my feet swell

So the line between time and cause is a little flexible here.

That is very common in Turkish.

The sentence has this structure:

• Ayakkabı dar olunca = subordinate clause
• ayaklarım şişiyor = main clause

So the full pattern is:

• [When X happens] + [Y happens]

This is a very common Turkish structure.

Literally:

• When the shoe is tight, my feet swell.

The conditional/time clause comes first, which is very natural in Turkish.

Yes. Here are some natural alternatives:

• Ayakkabılar dar olunca ayaklarım şişiyor.
  More explicitly plural: When the shoes are tight, my feet swell.

• Ayakkabılarım dar olunca ayaklarım şişiyor.
  More clearly: When my shoes are tight, my feet swell.

• Ayakkabı dar olduğunda ayaklarım şişiyor.
  Slightly more formal/literary: When the shoe is tight, my feet swell.

The original sentence is already natural; these are just variations in explicitness or style.