why do pedals undo

Team4Luke
Team4Luke Posts: 597
edited July 2012 in Workshop
pedals have an opposite thread, so should not come undone when pedalling however if your pedal is loose it will come fully undone, has happened to me and recent to a friend and I am trying to explain and find out why, is there a tiny part of a pedal revolution that is not against the threads, am I correct ?
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Comments

  • freezing77
    freezing77 Posts: 731
    Look up the term "precession" for a full explanation
    A precis
    "For a pedal, a rotating load arises from downward pedaling force on a spindle rotating with its crank making the predominantly downward force effectively rotate about the pedal spindle. What may be less evident is that even tightly fitting parts have relative clearance due to their elasticity, metals not being rigid materials as is evident from steel springs. Under load, micro deformations, enough to cause motion, occur in such joints. This can be seen from wear marks where pedal spindles seat on crank faces."[1]
  • Team4Luke
    Team4Luke Posts: 597
    excellent, I'm no mechanical expert but suspected this actually occurs.
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  • John.T
    John.T Posts: 3,698
    Or to give the obvious answer. Because they were fitted dry and not tight enough. :D
    My Fleet.

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