Amenex Associates, Inc.
Metals and Materials Consultants

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The mis-assembled bicycle's pedal became detached ... Why ?

	Here is a bottom view of the bicycle - an inexpensive imported model purportedly assembled by store personnel for the incredibly naive customer, who never noticed the cross threaded pedal.
	Perhaps the cyclist didn't notice the extreme pedal angle because he was pedalling with the arch of his shoe rather than the ball of his foot ... an educational lapse commonly in evidence on American streets.
	The pedal never struck the ground (especially in turns) because it was nearly perpendicular to the plane of the bicycle in the bottom-of-the-stroke position. Below you can see that the pedal is externally undamaged and nearly unworn.  It had been ridden about twenty miles on mostly level streets

	The pedal spindle hints at the solution to the puzzle. Note the wear pattern at the upset end in this view.  The pedal was retained on the spindle by a washer and rotary peening of the spindle.
	In another view at right angles to the view above, one can just see the indentation made by the washer on the bottom side.
	The inboard view of the pedal shows internal damage.  There are no separate bearings in this pedal.  The spindle simply rotates in direct sliding contact with the plastic housing.  There are no ball bearings like those that were standard before standards fell.  Below, the outboard view of the inside of the pedal showed evidence of wear between the aforesaid washer and the inside of the clearance space.
	SUMMARY: The pedal became detached because the extreme angle of the pedal spindle at the peak of the rider's power stroke (with the cranks parallel to the ground) caused an unforeseen increase in the endwise force as well as an unanticipated increase in the proportion of that force applied to the outboard bearing of the pedal.  The result was that the washer was forced to turn while under an offset axial load.  That wore the inside diameter of the washer until it came off the end of the pedal spindle, causing the rider's foot to slip off the crank.