In die bocht moet je voorzichtiger fietsen.

Because Dutch main clauses follow the verb-second (V2) rule.

The sentence starts with In die bocht. Once that element is placed first, the finite verb has to come next:

• In die bocht
  • moet
    • je
      • ...

So:

• Je moet in die bocht voorzichtiger fietsen.
• In die bocht moet je voorzichtiger fietsen.

Both are correct, but when you move In die bocht to the front, moet has to come before je.

Die here means that.

So die bocht is that bend/that turn.

Dutch demonstratives depend on the noun:

• de-word noun -> deze / die
• het-word noun -> dit / dat

Since bocht is a de-word noun, you get:

• de bocht
• deze bocht = this bend
• die bocht = that bend

In some contexts, die can feel a bit like English that particular.

Dutch usually says in de bocht / in die bocht for being in a bend / on a curve / while going through that curve.

English and Dutch do not always use prepositions in the same way. Even though English might say on that bend in some contexts, Dutch naturally uses in here.

So:

• in de bocht = in the bend / on the curve / while taking the turn

This is just the normal Dutch expression.

Bocht means a bend, curve, or turn, especially in a road or path.

Depending on context, English could translate it as:

• bend
• curve
• turn

So In die bocht could be understood as:

• In that bend
• On that curve
• At that turn

The exact English word depends on the situation, but the Dutch word is perfectly normal for a road bending.

Voorzichtiger is the comparative form of voorzichtig.

• voorzichtig = careful / carefully
• voorzichtiger = more careful / more carefully

So the sentence is not just saying cycle carefully, but cycle more carefully.

Dutch often forms the comparative by adding -er:

• groot -> groter
• langzaam -> langzamer
• voorzichtig -> voorzichtiger

Here it functions like an adverb, because it describes how you should cycle.

It modifies fietsen:

• voorzichtiger fietsen = to cycle more carefully

This is something English speakers often notice: in Dutch, the same form is often used where English would distinguish between an adjective and an adverb.

Compare:

• een voorzichtige fietser = a careful cyclist
• voorzichtig fietsen = to cycle carefully
• voorzichtiger fietsen = to cycle more carefully

So yes, it looks like an adjective form, but in this sentence it works adverbially.

Because Dutch usually does not create adverbs the way English does with -ly.

English:

• careful -> carefully

Dutch:

• voorzichtig -> voorzichtig

The same word can often mean both:

• careful
• carefully

And the comparative works the same way:

• voorzichtiger = more careful / more carefully

So voorzichtiger fietsen is the normal Dutch way to say cycle more carefully.

Literally, moeten often means must or have to, but in real Dutch it can also sound like should, depending on context.

So moet je here can mean:

• you must
• you have to
• you should

In a sentence like this, it often feels like practical advice or a warning rather than a strict legal obligation.

So depending on tone and context, English might translate it as:

• You have to cycle more carefully in that bend
• You should cycle more carefully in that bend

Because moeten is a modal verb, and modal verbs take a bare infinitive in Dutch.

So you say:

• Je moet fietsen = You must cycle
• Je kunt zwemmen = You can swim
• Ik wil gaan = I want to go

Not:

• Je moet te fietsen ❌

So in this sentence:

• moet je voorzichtiger fietsen

the infinitive fietsen appears without te.

Yes, absolutely.

That version is also correct:

• Je moet in die bocht voorzichtiger fietsen.

The difference is mainly emphasis and information structure.

• Je moet in die bocht voorzichtiger fietsen.
  Neutral statement.

• In die bocht moet je voorzichtiger fietsen.
  Emphasizes in that bend.

Dutch often moves an element to the beginning when it is the topic or the part the speaker wants to highlight.

It can do either, depending on context.

Je can mean:

• you = one specific person
• you in a general sense = people / one

So this sentence could mean:

• advice to one rider: You should cycle more carefully in that bend
• a general statement: You should be more careful when cycling in that bend

Dutch uses je very often in this general way, much like informal English you.

Yes, but it changes the meaning.

• In die bocht moet je voorzichtig fietsen.
  = In that bend, you should cycle carefully.

• In die bocht moet je voorzichtiger fietsen.
  = In that bend, you should cycle more carefully.

So voorzichtiger implies a comparison:

• more carefully than usual
• more carefully than before
• more carefully than in other places

That comparative meaning is important.

Because in Dutch, when you have a finite verb plus another verb in the infinitive, the infinitive often goes toward the end of the clause.

Here:

• moet = finite verb
• fietsen = infinitive

So the structure is:

• In die bocht | moet | je | voorzichtiger | fietsen

This is very common in Dutch:

• Ik wil koffie drinken.
• Je kunt hier parkeren.
• Wij moeten eerder vertrekken.

So fietsen at the end is exactly what you would expect after moeten.