Gotta love those doughnut spares (and where is he lately, anyway? [img]smile.gif[/img] )
A side note for them... they're only good for speeds up to around 55mph (90kph or so), and only good for about that many miles (or kilometers), too... about as close to disposable as you can get!
The only reason to keep one... if the designers made it fit perfectly in the car. You'll know if you try to put a real tire in and it just won't fit...