Originally Posted by Zouf
Your original post gave wrong direction for unscrewing the pedals. It's tighten with forward pedal, loosen with back pedaling. That's so a seizing pedal bearing won't unscrew the pedal. Had it in an old bike (remember those pedals with the pivot point above the pedal floor, with big threads?): Those used to be identical left/right, so I had one unscrew because of a tight bearing.
Actually a seizing pedal bearing WILL unscrew the pedal. But that rarely happens. What DOES happen is that the pedals can be unscrewed due to precession during rotation. In order to prevent that, the right hand side pedal has right hand threads, left hand has left-hand threads. This is counterintuitive because you'd think that would cause them to unscrew if loose, but actually due to precession, it makes them tighter as you pedal.
If you don't believe me, these people probably know what they're talking about
:
http://www.parktool.com/repair_help/FAQpedls.shtml
(original poster, check out this link on removing pedals).