hi, i'm looking for winter tires on my '05 xfire. what size can i get as rims and tires for it? i was thinking of buying mercedes winter mags. i know they fit, i just don't know what size is the smallest i can go. by the way i live in canada, so winters are rough here. please let me know and thank you for your help. also has anybody tried fitting wider tires in the back? what is the size we can fit, or does someone know the ratio upgrade for the tires, for example stock are 225/40/18, 255/35/19. what can be replaced if i go wider in the back??