Superb step-13s (8)

I believe the answer is:

grandpas

I'm a little stuck... Click here to teach me more about this clue!

'superb step-13s' is the definition.
I can't tell whether this definition defines the answer.

'superb step' is the wordplay.
'superb' becomes 'grand' (I can't justify this - if you can you should give a lot more credence to this answer).
'step' becomes 'pas' (I've seen this before).
'grand'+'pas'='GRANDPAS'

Can you help me to learn more?

(Another definition for grandpas that I've seen is " Relatives".)

I've seen this clue in The Independent.

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