Thank You!! Was curious when I brought it home but never gave it more thought until this thread.http://www.r3-forums.com/forum/538-tires/5753-changing-tire-sizes.html#post55601
We established it's there in case the chain slips off the sprocket to prevent it getting caught in the wheel. You'd have to be pretty neglectful/unobservant/idiotic to let the chain get that loose. I got rid of mine a long time ago.