distancing in question/request

[panicmonger]

I wondered if you were free tomorrow.

I know the past tense use of 'wondered' shows politeness, why the second verb, are, is also used in the past tense?

Is this "were" also used for indicating politeness?

Thank you for your help.

 

[panicmonger]

Or this "were" is used in the subjunctive mood?

please feel free to comment on it.

thanks