Darren Vicary

Hi can someone help me out, I am putting a set of 18" wheels on to my Alfa Romeo 147 1.9 JTDM and need to work out if I can carry a space saver wheel with a size of 125/80/15, the tyre size of the new wheels are going to be 225/40/18 !!! if not could I change the tyre on the space saver to get the right size in high. I only need it if I have a blow out or puncture to get me home.