Se o pneu estiver estranho, vamos parar no posto para colocar gasolina.

Because after se when you are talking about a possible future situation, Portuguese normally uses the future subjunctive.

• Se o pneu está estranho = sounds like a statement about something happening now, and it is usually not the natural choice here.
• Se o pneu estiver estranho = if the tire seems/is strange at some point in the future.

This is a very common pattern in Portuguese:

• Se chover, ficamos em casa.
• Se ele chegar cedo, saímos juntos.
• Se o pneu estiver estranho, vamos parar...

So estiver is the future subjunctive form of estar.

Estiver comes from the verb estar.

In this sentence, estiver estranho means something like:

• is strange
• seems odd
• looks unusual
• doesn’t seem right

With machines, objects, or body parts, Portuguese often uses estar estranho to mean that something seems off, abnormal, or suspicious.

So o pneu estiver estranho could suggest things like:

• the tire looks low
• it is making a weird noise
• it feels wrong somehow
• something seems unusual about it

Yes. Pneu means tire.

Portuguese usually uses an article where English often does not. So:

• o pneu = the tire
• um pneu = a tire

Even when English might say if a tire seems strange or just if the tire looks weird, Portuguese naturally keeps the article:

• Se o pneu estiver estranho...

That is completely normal.

Because in Portuguese, adjectives often come after the noun.

• pneu estranho = strange tire
• carro novo = new car
• casa grande = big house

In this sentence, though, the structure is slightly different:

• o pneu estiver estranho

Here estranho is not directly attached inside a noun phrase like pneu estranho. It is part of the predicate with estar:

• o pneu = the subject
• estiver = verb
• estranho = adjective describing the subject

So it works like the tire is strange / seems strange.

Vamos parar means we’re going to stop or let’s stop, depending on context.

Here it most naturally means:

• we’ll stop
• we’re going to stop

Vamos + infinitive is a very common way to talk about a near future action in Portuguese.

Examples:

• Vamos sair. = We’re going to leave.
• Vamos comer. = We’re going to eat.
• Vamos parar no posto. = We’re going to stop at the gas station.

In some contexts, vamos + infinitive can also sound like a suggestion:

• Vamos parar? = Shall we stop?

But in your sentence, it sounds more like a plan or decision.

No posto is a contraction of:

• em + o = no

So:

• no posto = at the station / at the gas station

In Brazil, posto by itself often means gas station, especially in everyday speech. More fully, people may say:

• posto de gasolina
• posto de combustível

But very often just posto is enough.

Be aware that posto can mean other kinds of station/post in other contexts, but in this sentence it clearly means a gas station.

Because parar em is the natural choice here.

• parar em algum lugar = to stop at some place

So:

• parar no posto = stop at the gas station

If you use ir ao posto, that means go to the gas station. But with parar, Portuguese normally uses em:

• Vamos parar no mercado.
• Paramos na farmácia.
• Vou parar no posto.

So the preposition comes from the verb expression parar em.

Para colocar gasolina means to put gas in / to get gas / to fill up.

Literally:

• para = in order to / to
• colocar = to put
• gasolina = gasoline

So the structure is:

• vamos parar no posto para colocar gasolina
• we’re going to stop at the gas station to get gas

In natural English, you probably would not say put gasoline as often. But in Portuguese, colocar gasolina is very normal and understandable.

Other common options in Brazilian Portuguese are:

• abastecer = to fill up / refuel
• colocar combustível = to put fuel in
• encher o tanque = fill the tank

For example:

• Vamos parar no posto para abastecer.
• Vamos parar no posto para encher o tanque.

Because Portuguese often uses mass nouns like gasolina, água, dinheiro, leite, etc. without an article when speaking in a general sense.

So:

• colocar gasolina = put in gas / get gas
• beber água = drink water
• comprar pão = buy bread

You could use an article in other contexts, but here the general idea is just get gasoline, so no article is needed.

Yes, absolutely.

• Vamos parar no posto para colocar gasolina.
• Vamos parar no posto para abastecer.

Both are natural.

The difference is mainly this:

• colocar gasolina is very transparent and literal: put gas in
• abastecer is a common verb meaning refuel / fill up

If you are learning, colocar gasolina is easy to understand. If you want a very common real-life alternative, abastecer is excellent.

Yes, gasolina is the normal word for gasoline in Brazil.

Be careful with gás:

• gasolina = gasoline / gas
• gás = gas, but usually things like cooking gas or gas in a general sense, not what you put in a car

So at a gas station, for a regular car, you would normally say gasolina, not gás.

It usually implies that something seems wrong, off, or suspicious about the tire.

In everyday usage, estranho often means more than just weird-looking. It can suggest:

• unusual
• not normal
• concerning
• not functioning as expected

So in this context, a learner should understand it more as:

• if the tire seems off
• if something seems wrong with the tire

rather than only if the tire is weird in a humorous sense.

The sentence has two main parts:

1. Se o pneu estiver estranho

   • if the tire seems strange / if something seems wrong with the tire

2. vamos parar no posto para colocar gasolina

   • we’re going to stop at the gas station to get gas

So the pattern is:

• Se + future subjunctive clause, main clause

A useful template is:

• Se + [possible future condition], [what we will do]

Examples:

• Se ele chegar cedo, vamos sair.
• Se chover, vamos ficar em casa.
• Se o pneu estiver estranho, vamos parar no posto...

Yes. Portuguese can also put the if-clause after the main clause:

• Vamos parar no posto para colocar gasolina se o pneu estiver estranho.

This means the same thing.

The version with the se clause first can sound a little more natural when you want to present the condition before the action:

• Se o pneu estiver estranho, vamos parar...

That order is very common and clear.