Learn Spanish (Spain): Como el neumático no tiene aire, no podemos viajar. - Since the tire has no air, we cannot travel.

When stating a reason at the very beginning of a sentence, Spanish prefers Como. You generally cannot start a sentence with Porque to mean 'because.' If you wanted to use porque, you would flip the order: No podemos viajar porque el neumático no tiene aire.

Could I use the subjunctive here and say Como el neumático no tenga aire?

Not if you mean 'since it has no air.' When como introduces a known, factual reason, it takes the indicative mood (tiene). If you used the subjunctive (tenga), it would change the meaning to a conditional warning: 'If the tire has no air (when we check it later), we will not be able to travel.'

What is the difference between a neumático, a rueda, and a llanta in Spain?

Neumático specifically means the rubber tire. Rueda is the general word for the entire wheel. In Spain, llanta usually refers only to the metal rim that holds the tire, although in much of Latin America, llanta is the standard word for the rubber tire itself.

Why use tiene instead of hay for 'has no air'?