What is the other tyre like? I think you would be best to replace the rears now with the Michelin Pilot Sport 4S (successor to the Super Sports). I would recommend using Discount Tyres in Blanchardstown. They are also doing an offer on Michelin tyres at the moment and have the alignment equipment.

Discount Tyre & Autocare | Tyres and Servicing | Dublin (discounttyres.ie)