Das Fahrradschloss, mit dem ich mein Rad am Bahnhof festmache, ist leider schwerer als gedacht.

In German compound nouns, the last part determines the grammatical gender.

• das Schloss = the lock
• das Fahrradschloss = bicycle lock

Because Schloss is neuter, the whole compound is neuter too:

• das Schloss
• das Fahrradschloss

This is a very important rule for German compounds:

• das Haus → das Gartenhaus
• der Tisch → der Küchentisch
• die Tasche → die Handtasche

So even though Fahrrad is also neuter, what really decides the gender here is the final element: Schloss.

Yes, this is completely normal in German. German often combines nouns into one longer noun.

Here:

• Fahrrad = bicycle
• Schloss = lock

So:

• Fahrradschloss = bicycle lock

This kind of compound is extremely common in everyday German. English often uses separate words where German prefers one compound word.

Examples:

• Bahnhof = train station
• Haustür = house door / front door
• Schlüsselbund = key ring

So Fahrradschloss is not unusual at all.

The comma marks the start of a relative clause:

• Das Fahrradschloss, mit dem ich mein Rad am Bahnhof festmache, ...

The main noun is das Fahrradschloss, and the relative clause adds extra information about it:

• mit dem ich mein Rad am Bahnhof festmache
• with which I fasten/lock my bike at the station

German uses commas around relative clauses much more strictly than English does. In this sentence, the relative clause is inserted into the middle of the main sentence, so it is separated by commas on both sides.

Main clause:

• Das Fahrradschloss ist leider schwerer als gedacht.

Inserted relative clause:

• mit dem ich mein Rad am Bahnhof festmache

Because mit always takes the dative case.

The relative pronoun refers back to das Fahrradschloss. Since that noun is:

• neuter
• singular

the relative pronoun starts from das in nominative, but after mit it must become dative:

• nominative: das
• dative: dem

So:

• das Fahrradschloss
• mit dem = with which

The relative pronoun must match the noun in gender and number, but its case is decided by its role inside the relative clause.

Here is the logic:

• Antecedent: das Fahrradschloss → neuter singular
• Preposition: mit → requires dative
• Therefore: mit dem

This is a relative clause. It describes das Fahrradschloss.

You can break it down like this:

• mit dem = with which
• ich = I
• mein Rad = my bike
• am Bahnhof = at the station
• festmache = fasten/secure

Literally:

• the bike lock, with which I secure my bike at the station

In a German subordinate clause like this one, the conjugated verb usually goes to the end:

• ..., mit dem ich mein Rad am Bahnhof festmache

That final verb position is one of the most important patterns in German sentence structure.

Because this is a subordinate clause introduced by a relative pronoun (mit dem).

In German:

• In a main clause, the conjugated verb is usually in second position.
• In a subordinate clause, the conjugated verb usually goes to the end.

Compare:

Main clause:

• Ich mache mein Rad fest.

Relative/subordinate clause:

• ..., mit dem ich mein Rad am Bahnhof festmache

So the verb moves from its normal main-clause position to the end of the subordinate clause.

festmachen is a verb meaning things like:

• to fasten
• to secure
• to tie up
• to lock in place

In the context of a bicycle lock, it means something like:

• to secure my bike
• to lock my bike up
• to fasten my bike to something

It is a separable verb:

• infinitive: festmachen
• main clause: Ich mache mein Rad fest.
• subordinate clause: ..., weil ich mein Rad festmache.

Notice what happens:

• In a main clause, the prefix often separates: mache ... fest
• In a subordinate clause, it stays together: festmache

Yes. In this sentence, Rad is just a shorter, very common way to say Fahrrad.

• das Fahrrad = bicycle
• das Rad = bike / wheel, depending on context

In everyday speech, Rad often means bicycle when the meaning is obvious.

So:

• mein Rad = my bike
• mein Fahrrad = my bicycle

Both are natural here. Using Rad avoids repeating Fahrrad immediately after Fahrradschloss, so it sounds smoother.

am is a contraction of an dem.

• an dem → am

So:

• am Bahnhof = at the station

This contraction is extremely common and usually preferred.

Why dative here? Because the phrase expresses location, not motion toward a destination.

Compare:

• Ich bin am Bahnhof. = I am at the station. → location → dative
• Ich gehe an den Bahnhof. = I go to the area by the station. → direction → accusative

In your sentence, the bike is being secured at the station, so dative is used:

• am Bahnhof

schwerer is the comparative of schwer.

• schwer = heavy
• schwerer = heavier

German usually forms the comparative by adding -er:

• klein → kleiner
• langsam → langsamer
• schwer → schwerer

So:

• ist schwerer = is heavier

The full phrase is:

• ist leider schwerer als gedacht
• is unfortunately heavier than expected/thought

als gedacht is a very common shortened expression in German. It means something like:

• than expected
• than I thought
• than one had thought

Literally, gedacht is the past participle of denken:

• denken = to think
• gedacht = thought

The full idea is something like:

• schwerer, als ich gedacht habe
• heavier than I had thought

But German often shortens this to:

• schwerer als gedacht

This kind of ellipsis is very common, especially after comparatives:

• größer als erwartet = bigger than expected
• teurer als geplant = more expensive than planned
• schwerer als gedacht = heavier than thought/expected

So the missing subject is understood from context.

Both are possible, but they have slightly different sentence structures and emphasis.

Here the sentence starts with the subject:

• Das Fahrradschloss ist leider schwerer als gedacht.

This follows the normal main-clause pattern:

1. subject: Das Fahrradschloss
2. verb: ist
3. middle field: leider
4. rest: schwerer als gedacht

You could also say:

• Das Fahrradschloss ist leider schwerer als gedacht.
• Leider ist das Fahrradschloss schwerer als gedacht.

The second version puts more emphasis on unfortunately from the very beginning.

So the original sentence is simply the neutral, natural way to say it.

leider means unfortunately or sadly.

It expresses the speaker’s attitude:

• the lock being heavier is a negative or disappointing fact

So:

• ist schwerer als gedacht = is heavier than expected
• ist leider schwerer als gedacht = is unfortunately heavier than expected

It does not change the grammar of the sentence very much; it adds the speaker’s reaction.

Yes, but it would usually sound less natural here.

• mit dem = the normal relative pronoun form
• mit welchem = also grammatically possible

So this is possible:

• Das Fahrradschloss, mit welchem ich mein Rad am Bahnhof festmache, ...

But in everyday German, relative clauses usually prefer:

• der / die / das
• dem / der / den, etc.

So mit dem is the more standard and idiomatic choice in ordinary speech and writing.

Because German often uses a shortened comparative expression after als.

Instead of saying the full clause:

• als ich gedacht habe

German often reduces it to just a participle:

• als gedacht

This happens especially when the full meaning is obvious.

Compare:

• besser als erwartet = better than expected
• schneller als geplant = faster than planned
• schwerer als gedacht = heavier than thought/expected

So this is not a mistake or incomplete German. It is a normal, compact pattern.

If you remove the inserted relative clause, the main sentence is:

• Das Fahrradschloss ist leider schwerer als gedacht.

That is the core structure:

• subject: Das Fahrradschloss
• verb: ist
• predicate/adjective phrase: leider schwerer als gedacht

The part in commas:

• mit dem ich mein Rad am Bahnhof festmache

just gives extra information about which lock we are talking about.

This is a useful way to analyze long German sentences:

1. find the main clause
2. identify inserted subordinate clauses
3. read each part separately