Ich pumpe den Reifen auf, bevor wir losfahren.

I pump up the tire before we set off.

Breakdown of Ich pumpe den Reifen auf, bevor wir losfahren.

• ich: I
• wir: we
• bevor: before
• der Reifen: the tire
• aufpumpen: to pump up
• losfahren: to set off

Questions & Answers about Ich pumpe den Reifen auf, bevor wir losfahren.

What type of verb is aufpumpen and why is the particle auf at the end of the main clause?

aufpumpen is a separable-prefix verb. In main clauses the prefix (auf) detaches from the verb stem (pumpen) and moves to the very end of the clause, while the finite verb form (pumpe) stays in the second position.
Example: Ich pumpe … auf.

Why is den Reifen in the accusative case?

Because den Reifen is the direct object of aufpumpen. Reifen is masculine (der Reifen), and when a masculine noun is the direct object (accusative), der changes to den, giving den Reifen.

Why is there a comma before bevor?

bevor is a subordinating conjunction. German always requires a comma before a subordinate clause introduced by such conjunctions. Here it separates the main clause from the time clause:
Ich pumpe den Reifen auf, bevor wir losfahren.

In the subordinate clause bevor wir losfahren, why does losfahren remain one word and appear at the end?

Two rules apply at once:

1. losfahren is also a separable-prefix verb.
2. Subordinate clauses introduced by a subordinating conjunction (bevor) send the finite verb (here fahren with its prefix los) to the very end. In subordinate clauses the prefix reattaches, so you get one word at clause-final position.

Could you place the subordinate clause at the beginning of the sentence? How does the word order change?

Yes. You’d still use a comma, and the main clause verb remains in second position (inversion happens if you front another element):
Bevor wir losfahren, pumpe ich den Reifen auf.
Notice after the comma the verb pumpe comes before the subject ich.

Could you use another verb instead of aufpumpen to express “inflate the tire”?

Yes. For example:

• Ich fülle den Reifen mit Luft auf, bevor wir losfahren.
  (Here füllen … auf is another separable verb; mit Luft specifies what you’re filling with.)
• You could also say aufblasen, but that often implies using a mouth-blowing action or a pump without stressing the mechanical process as much.

What nuance does losfahren carry, and why not just use fahren?

losfahren means “to set off” or “to depart,” emphasizing the moment of starting a journey. fahren alone simply means “to drive” or “to go” without highlighting that initial departure. Since the sentence talks about “before we set off,” losfahren is the precise choice.