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PostPosted: Fri Nov 16, 2012 10:37 am 
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I'm curious to see if anyone know how this standard came to be? It seems like pedals the threading should be the opposite direction so that the motion would be in the tightening direction and not the direction that loosens the bottom bracket.

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PostPosted: Fri Nov 16, 2012 12:09 pm 
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No, if you think about the forces dragging on the cup, the pedalling forces tighten an English threaded cup. Try riding a slightly loose Italian cup you will find the RHS fixed cup comes undone in minutes. After one experience on an Italian (i.e. normal thread both sides of the frame) you would quickly develop the English standard!


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PostPosted: Fri Nov 16, 2012 1:30 pm 
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I'd rather have the bigger properly torqued Italian cups! :mrgreen:

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PostPosted: Fri Nov 16, 2012 1:32 pm 
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:smartass: http://en.wikipedia.org/wiki/Precession_(mechanical) :smartass:

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PostPosted: Fri Nov 16, 2012 6:40 pm 
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Left hand threads (counterclockwise to tighten) on the drive-side cups is strange as the friction from pedaling is clockwise which tends to loosen the cups..


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PostPosted: Fri Nov 16, 2012 6:49 pm 
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ZeroG wrote:
friction from pedaling is clockwise which tends to loosen the cups..

It would, if we didn't have bearings inbetween cups and spindle. Luckily we do, so there is not enough friction transferred to overcome static friction between torqued BB cups threads and frame BB threads. As such the other thing we have to deal with is precession (see monkeyburger's post above) which is the reason for English thread standard.


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PostPosted: Fri Nov 16, 2012 7:04 pm 
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monkeyburger knows his stuff.

Its a wonder the Italians have perservered with their sub-standard, standard.


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Posted: Fri Nov 16, 2012 7:04 pm 


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PostPosted: Mon Nov 19, 2012 5:42 am 
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In the past, BB cups have nothing pressing them in other than the threads.

With today's crankset designs, this issue seems less relevant.

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