La grave hasn’t got the best biking, it is a bit too steep and there is not much scope there, probably 2 days worth. Just down the valley you have Les Deux alpes and Alp d’huez about an hour away, and in the other direction you have got mont genevre and les Orres again about an hour away and are all good.
if you want to stay in la grave there are two decent campsites, but it is quite a sleepy little town and if you go down to Briancon there are a lot more campsites and activities on offer.
Are you after DH riding or more xc riding?