Urban Velo

Bike Threading 101

Bike Threading

The old “righty tighty, lefty loosey” rule doesn’t always apply when you’re working on bicycles.

Right- and left-hand threads can be easily visually differentiated. With the male end of the bolt, or in this case pedal axle, pointed up, right-hand threads slope up and to the right while left-hand threads slope up and to the left.

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One Comment

  1. jamesJuly 21, 2008 at 11:47 pm

    Two things. First, precession will not unscrew a bottom bracket or a pedal because the force of precession perpendicular to both the force applied and the circular motion via the “right hand rule” (not the righty tighty rule btw). This force would cause the bb to teetor left to right and the cranks to twist and untwist, but always perpendicular (and thereby not affecting any of the threaded systems. Second, the primary force that would unscrew any of the mentioned systems would be the friction transferred via bearings, this would tend to unscrew both cups in a bb and pedals. The unscrewing of the bb cups takes advantage of the lockring to keep it in good adjustment, the unscrewing of the pedals is a safety mechanism for our shins. If this doesn’t seem to make sense, remember that toe clips and fixed gears predate reliable ball bearings. The reverse thread on the left pedal is the last line against the worst shin splint imaginable from toe clips and fixed geared pedal bearing lockup. As an aside, precession is the cause of that weird tendency for your mountain bike equipped with that cool lefty fork to yaw to one side. The downward force is essentially equal on double bladed forks, but that poor lefty, while strong enough, still steers outside the box thanks to precession.

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