Reply to thread

I have 2 road bikes.  The first is a fairly new (about 2 or 3 years) Schwinn and the other is a vintage Schwinn.  When riding, both randomly switch gears without me doing anything.  The newer bike also has a problem where the chain locks up and I can't pedal, but it only lasts for a few feet.  Generally the vintage bike switches gears on me when I hit a bump.  Any advice on how to fix this?  I'm thinking about taking it into a bike shop to have them look at it but it'd be nice if I could fix it up myself if it's simple enough.  I'm more concerned about the new bike since I need it by Saturday for a bike-a-thon.  Thanks!