I read all the responses, BUT, a good tire shop can match the diameter and tread of your existing tires. I have sold new and used cars, tires and accessories, and don't "buy" that line. What does your manual tell you? You could also call contact Subaru customer support. So... if you put your donut spare on your Subaru, it destroys the transaxles or what? Sorry for the rant, but.... my guess is that half their customers buy all four tires no questions asked, which means it works for the sales guy 50% of the time. I would just get some solid facts before I spent that kind of cash.