In the way home tonight, Mrs. Yokel ran over a nail and got a flat. What a woman...changed the tire on her own and drove home! To the question: the spare is marked with the "temporary use only" and 50mph warnings. The manual also lists a bunch of warnings about using the spare. It looks like a standard 20" wheel and tire to me. We have the 22" wheels, but using an online tire fit calculator, it looks like the same diameter. Any idea why the warnings?