I own a 2005 Legacy SPEC.B 3.0R fitted with (the default) 18-inch aluminum-alloy wheels.
A (non-Subaru) garage has used my (spare) 18-inch aluminum-alloy wheel for winter tires - and just put a 17-inch yellow flat temporary iron wheel as my new spare wheel. They claim 17-inch is "the standard" for my car.
This thread makes it doubtful that Subaru would use a 17-inch spare wheel:
Was the garage right? Can I really use a 17-inch temporary wheel with three 18-inch wheels?
Thank you for your assistance!