While I was researching biking I picked up a few things that might answer your questions. Yes, they make the bike go faster, but they aren't for offroading where they're likely to hit a rock large enough to make them go off balance. And I think it was the faster you go, the stabler you are. I also read that in some places biking on the sidewalk is illegal. In my state (Kansas) at least a bike has the exact same rights as a vehicle. Yay for bike lanes, Biking on sidewalks is illegal, but I think there is an exception to that rule...like for a short period of time or something...