Information on how Hiroki Ono has modified the Birdy to take a double
chainwheel can be found at the site
http://www.cup.com/onohiroki/bike-bd-1.html#2x7.
Hiroki now has a page in English at
http://www.cup.com/onohiroki/bike-bd-1-e.html.The
photograph on the right shows the mechanism for more views, please visit
Hiroki's site. This excellent photo is courtesy of Hiroki Ono.
Chris Dent has one of the earlier Birdy Blues, which were fitted with
a 7-speed derailleur rather than the current Sachs 3x7. Chris, like some
others, found the overall gearing rather on the high side and has fitted
an 11-34 tooth sprocket set. In addition he has fitted a smaller
chainwheel (52 teeth). The usual problem in doing this is that the plastic
chain retention rings etc are only available in the original size, which
of course is far too big for the smaller chainwheel. Chris has overcome
this problem by using the original 56 tooth chainwheel in the position of
an inner chainwheel, purely acting as a chain retainer, not for taking the
chain, and a modified bracket which retains the chain on the outside and
lowers the normal upper frame retention boss - see the pictures for
details. The PCD of the crankset retaining bolts is standard racing
Shimano (130mm), so that the 52T ring was readily available. Chris has
also fitted a Shimano XT GS rear mech, the cage of which is 2cm shorter
than the usual XT, LX and STX RC super long cage derailleurs, so that
there is more ground clearance as well as coping with the 34T sprocket.
My thanks to Chris for filling in the details on the system.
Birdy Red is admired by a white duck at Badger.
This
is a standard 9-speed 11-34 Shimano cassette fitted to a Birdy Red, with
the current LX changer mechanism. Unfortunately the 11-34 sprocket set is
currently only available in one of the more expensive Shimano versions.
The 11-34 7-speed cassette used by Chris Dent and described earlier is one
he has built up himself, using sprockets taken from a variety of sets. The
9-speed system, controlled by Rapidfire lever, runs very sweetly, with
very smooth changes - much less clunky than the original Alivio system. In
the lowest gear the chain rubs against the inner plastic chain retainer
plate, and sounds rather unhappy - but the same happened with the original
7-speed set up. In second gear there is very slight rubbing, and only very
slight signs of distress, while in the higher gears the chain line places
less strain on the system and runs very smoothly. This suggests that the
strain on the chain might be less overall if the chainwheel were
repositioned, but this would give a less satisfactory line in top gear,
and the bike runs in this gear quite often, whereas the lowest gears are
used relatively infrequently. The new, lower bottom gear has only been
brought into play so far for testing.
Steve Parry has fitted a mountain drive bottom bracket to his Birdy Red. He has also upgraded to Campag gears. A photograph can be found on The Folding Society pages, and it is hoped that an article on this and the other mods that Steve has made will appear in a future issue of A to B magazine - or on these pages sooner if I can get hold of a copy!
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Last updated: 24 December 2001