Steven Maasland pointed out:
"""
there is a neat bike for sale on French ebay:
http://cgi.ebay.fr/
Dave Anderson wrot: """ wow. First time I have ever seen or heard of one. What advantage--if any--does this contraption supply? """
I say:
Here is a nice blow up of a 4 speed retrodirect.
http://www.m-gineering.nl/
This basically allows one to pedal forward to get the high gear and backwards to get the low gear. The key to it is that both rear cogs freewheel independently. The weird chain pattern makes it so that when pedaling forward, the small cog engages, but the rear one rotates backwards. When pedalling backwards, the big cog engages (goes forward) and the little cog rotates backwards (freewheeling). If you have trouble figuring it out, print out one of the pictures of the chainline and trace the path of the chain with a pencil. Both freewheels are standard (not backwards). You should see that the chain turns one freewheel one way and the other the opposite.
Now, who has a nice picture of the two speed track set up that some people used in the kilo where there are two cogs, one loose one not and as you pedal the loose one threads on and engages giving you a new gear a few tens of pedal strokes into the race. Two cogs, two chains and two chainrings?, I can't remember how it worked.
Tarik
=====
Tarik Saleh
PO Box 1326, Knoxville, TN 37901
tsaleh at rocketmail dot com
Bicycles, bicycles, bicycles:
http://www.engr.utk.edu/
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