Originally Posted by
FeartheReign
Figuring this stuff out is part of the fun, and the only reason that I bought the bike, er, box of parts. I have been to one bike store with less than stellar results, the guy I talked to had less of a clue about bikes than I do.
OK, but in passing, it is often the case
at any bike store that there are only one or
two individuals who actually know their ass from
first base, bicyclewise. Your job in the future is
to figure out who that reliable source is.
If I find a BB that is listed as "Bottom Bracket, 68 73 x 113mm", I think that I understand that it will fit in a 68 or 73mm bottom bracket, but what does the 113mm indicate? Is it the space between the crank arms? Or is it the length of the shaft?
What this designation indicates, as you have
correctly surmised, is that the unit in question
will work on either a 68 or 73 width BB shell
(courtesy of spacers or different width threaded
installation rings that thread into the same
threads as the cups in a traditional BB spindle
and cup unit.
The 113 is, indeed the length of the shaft overall
including the tapers. So if you have 73mm lost
inside the shell, you need to figure out how much
additional length you require for your particular
use. In addition, you need to figure out if you
want a longer length (say for a double or triple
chainring) on the drive side. You also need to
be aware of the chain line (which you can eyeball
usually from the back and front) so that the chain
runs roughly straight between the front cogs
(chainwheels) and the middle cog on your rear
cluster.
Also, if we're talking square taper cranks, you
need to be aware that either ISO or JIS taper
usually works with most cranks, but just to make
the whole thing more amusing, not always.
Look here:
http://www.sheldonbrown.com/bbsize.html
and here:
http://www.sheldonbrown.com/bbtaper.html
and finally here:
http://www.sheldonbrown.com/cribshee...mbrackets.html
but if you're dealing with standard BSA
threading and a sealed replacement unit,
this last is mostly extraneous information.
What you're doing is not particularly simple
to calculate, but will prove quite educational
if that is your purpose.
Lastly, look here at the Phil Wood site:
http://www.philwood.com/products/bbhome.php
http://philwood.com/store/page30.html
Although you don't want to buy one of
these for a CL basket bike, the last reference
is a great educational resource in the variety
of Square taper BB axle lengths, tapers, and
configurations that exist in the various bikes
that have been produced over the years.
Phil Wood makes something to fit almost
everything, except your pocketbook.
