Why not use cheap "non aluminium" wheels? So not tires alone but the complete with steel wheels.
This has some advantages: the original wheels stay clean no corrosion, if you hit somthing like a curb no damage to the expencive wheels, easy to swap no running to your dealer 2 times a year, you have more year's before you have to change the expencive Michelin pilot's, cheaper then finding winter tires 18" & 19", you have a real spare wheel in summer & winter times

down part: it is ugly compared to the original wheels.

Not what you asked but this is what I will do if I receive my X-fire
Grtz,
Nean