Što je uspon strmiji, to idemo sporije.

It is a very common Serbian pattern used for proportional comparison:

• Što X, to Y
• English equivalent: the more X, the more Y / the X-er, the Y-er

So this sentence uses the same idea as English The steeper the climb, the more slowly we go.

A few more examples of the same pattern:

• Što više učim, to više znam.
  The more I study, the more I know.

• Što je hladnije, to manje izlazimo.
  The colder it is, the less we go out.

This is one of the most useful sentence patterns in Serbian.

No. In this sentence, što does not mean what.

Here, što is part of the comparative construction što ..., to .... In that pattern, it works more like:

• the more
• the -er

So in this sentence, što is grammatical, not interrogative.

That is why you should not read Što je uspon strmiji... as a question like What is steeper.... It is the first half of a comparative statement.

Je is the 3rd person singular present form of biti = to be.

The first clause is built like this:

• uspon = the climb / ascent
• je = is
• strmiji = steeper

So literally, that part is something like:

• the climb is steeper

In Serbian, when an adjective is used as the main description of something, you usually need biti:

• Uspon je strm. = The climb is steep.
• Uspon je strmiji. = The climb is steeper.

Then this gets placed into the što ..., to ... pattern.

Because the sentence needs the comparative form, not the basic form.

• strm = steep
• strmiji = steeper

The whole construction compares degrees. English does the same thing:

• The climb is steep → plain description
• The steeper the climb... → comparative

So Serbian also uses the comparative adjective:

• strmiji

Since uspon is a masculine singular noun, the adjective also appears in masculine singular form:

• uspon → masculine singular
• strmiji → masculine singular comparative

Because sporije is an adverb, while sporiji is an adjective.

Here, the word describes how we go, not what we are like.

• ići sporije = to go more slowly
• sporije modifies the verb idemo

Compare:

• sporiji ljudi = slower people
  → adjective

• idemo sporije = we go more slowly
  → adverb

So:

• strmiji describes the noun uspon
• sporije describes the verb idemo

That is why the forms are different.

Uspon is in the nominative singular.

Why? Because it is the subject of the clause:

• Uspon je strmiji.
  The climb is steeper.

In Serbian, the subject is normally in the nominative case.

So here:

• uspon = nominative singular
• strmiji agrees with it in gender, number, and case

Because Serbian often leaves out subject pronouns when the verb form already makes the subject clear.

• idemo = we go

The ending -mo already tells you it is we, so Serbian usually does not need mi.

Compare:

• Idemo sporije. = We are going more slowly.
• Mi idemo sporije. = We are going more slowly.
  This is also possible, but mi adds emphasis or contrast.

So the sentence sounds natural without mi.

In this construction, to pairs with što to create the full correlative pattern:

• što ..., to ...

It signals the second half of the relationship:

• the more X, the more Y

You can think of it as helping to connect the result or corresponding change in the second clause.

So:

• Što je uspon strmiji, to idemo sporije.

has a balanced structure:

• first half: changing condition
• second half: corresponding result

In this kind of sentence, to is very natural and standard.

Yes, a little.

The basic pattern stays the same, but Serbian allows some flexibility, especially in the second clause.

For example, these are natural:

• Što je uspon strmiji, to idemo sporije.
• Što je uspon strmiji, to sporije idemo.

The difference is mostly emphasis:

• idemo sporije = neutral
• sporije idemo = slightly stronger focus on more slowly

The first clause is usually kept together as Što je uspon strmiji.

Yes, depending on context.

Uspon can refer to:

• an ascent
• a climb
• an uphill stretch
• an incline / upward slope

In this sentence, the most natural English choices are usually:

• the climb
• the ascent
• the incline
• sometimes the hill if the context is casual

A learner should notice that Serbian often uses a noun like uspon where English might choose different words depending on the situation.

Yes, very common.

You will hear and read što ..., to ... often in both spoken and written Serbian. It is a basic way to express proportional relationships.

Useful examples:

• Što više radiš, to više zarađuješ.
  The more you work, the more you earn.

• Što sam stariji, to sam mirniji.
  The older I am, the calmer I am.

• Što ga bolje poznajem, to mi je zanimljiviji.
  The better I know him, the more interesting he seems to me.

So this sentence is not unusual or literary; it is a very normal Serbian structure.

Yes, absolutely.

It is a complete complex sentence made of two linked clauses:

1. Što je uspon strmiji
2. to idemo sporije

Together they express one full idea. Serbian does not need anything else here.

Punctuation-wise, the comma is important because it separates the two linked parts of the comparative structure.