Originally Posted by
rm -rf
If the low limit screw is set too far, it'll allow the chain to go past the large cog, into the spokes. Then the derailleur catches on the spokes, and rips it off the bike. It'll need spokes, derailleur, and often the frame is damaged too. An expensive problem.
Had a local shop pull this crap on me earlier this year, be very careful! I had to replace my wheels and rear derailleur, luckily my my frame pulled through or I might have accidentally been forced to drive my car through their front door (was pretty damn mad though this shop has always been beyond great otherwise, first road bike too!). Small adjustment, big damage..