The resolution of the pedaling forces is such that an RH threaded cup on the left side of the bike (traditionally the adjustable cup) and an LH threaded cup on the right side of the bike (traditionally the fixed cup) will tend to be further thightened by pedaling. Thus from the perspective of keeping the cups tight, English and Swiss BB's were the "correct" design, while Italian and French were "wrong". In practice, the tendency of French and Italian cups to loosen was probably only a problem in the first couple of thousand km or so, as we've all encountered French and Italian fixed cups on 25 year old frames that were difficult to remove, even with the proper tools. I did have the Italian fixed work loose on my early 80's Masi Prestige after about 400 km of use.
I've long said that the technically correct ISO BB standard would have been Swiss, since it was metric, and had the correct LH thread on the fixed cup. But of course that decision was made based on market share, not technical logic. At least the English thread anointed ISO did happen to have the "correct" LH fixed cup as well.
Regards,
Jerry Moos
Big Spring, Texas, USA
> From: r cielec <teaat4p@yahoo.com>
\r?\n> Subject: [CR] Bottom Bracket Cups & Threads - Why do they stay tight or loosen?
\r?\n> To: "Classic Rendezvous" <classicrendezvous@bikelist.org>
\r?\n> Date: Thursday, September 17, 2009, 1:45 PM
\r?\n> Ahoy !
\r?\n> The recent discussion of Swiss threads has prompted me to
\r?\n> expose another empty space in my head where knowledge should
\r?\n> have been filed many years ago.
\r?\n>
\r?\n> Bottom bracket cups and threads:
\r?\n> Any mechanical engineers out there who can explain why the
\r?\n> cups remain tightened or why they loosen ( I mean with
\r?\n> proper installation not because of error, cross-threading,
\r?\n> neglect) ?
\r?\n> Re: Threads are opposed RH and LH ? Does it matter which
\r?\n> side is RH or LH ? Can LH on right with RH on left still
\r?\n> keep the bb cups tight?
\r?\n> Would a LH-LH loosen up?
\r?\n> Why Italian RH-RH and only one lock ring?
\r?\n>
\r?\n> Thanks
\r?\n>
\r?\n> Richard Cielec
\r?\n> Chicago, Illinois; U.S.A.
\r?\n>
\r?\n>
\r?\n>
\r?\n>
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