I don't know about foresters, but I drive a bug and there aren't many cars with a backseat smaller than a bug, and I've fit a whole variety of rear facing carseats in the back (I babysit for some of my daughter's "friends"). They always fit, the only problem being that the passenger seat has to be slid way forward, so my husband couldn't ever sit in the passenger seat (fine with me, I didn't ever want to drive). However, you can try it out to be sure, and return it right away if it's too big. However, I read somewhere (consumer reports, maybe?) that if you're looking for value a Britax Marathon is overpriced for what you get, and that the mid priced Britax (which is smaller, too) is a better value, and just as safe. They also said a cheaper carseat (Evenflo, maybe?) was also just as good.