Jerry,
My KOF Eisentraut sports a far-off-topic Campi Chorus Racing Triple 9- speed drivetrain (originally 30--40-52 up front, 13-27 in the back). The gearing--just like my 41-52 Campi NR double of long ago--was not low enough for me.
(Sorry Dale--This off-topic drive train is the only example I have to make a point that applies to vintage drivetrains, too.)
Because we have steep local hills and my right leg was weakened by a 1970 rock climbing accident that "modified" the orthopedics of my personal drivetrain, I sought the advice of Stone's Cyclery, my LBS, to lower my gearing. The rear (cassette) was maxed out, but...
Dennis set up my Racing Triple with a 24T inner ring. The shifting works very well, considering that the FD's capacity has been exceeded by a fair amount, but using a "chain minder" inside the 24T ring is necessary to keep from jamming the chain between the crank spider and the BB during the occasional dropped-chain incident. (It saves on drivetrain hardware replacement costs: jammed or broken chains and crank arms, mangled derailleurs. Not every shift I make is a smooth or sensitive one, and sometimes I just forget where I put my chain on the cogs.)
Anyone using an on-topic drive train set up either near, at, or beyond the stated limits of the derailleurs' rated capacities can also benefit from using a "chain minder," even if using one is also off-topic.... :-)
Using one can prevent irretrievably jamming or destroying vintage parts, like the Stronglight 99 crank set and Simplex LJ derailleurs that will go on my Allegro. After all, the gearing on the Allegro will have to put up with the same "under-geared" engine that my Eisentraut does, and the local hills will not soften their angles for a vintage bike...
Jon Spangler Alameda, CA USA
On Feb 7, 2010, at 10:10 AM, <classicrendezvous-request@bikelist.org>
<classicrendezvous-request@bikelist.org> wrote:
>
> Message: 2
> Date: Sun, 7 Feb 2010 08:42:25 -0800
> From: Jerome & Elizabeth Moos <jerrymoos@sbcglobal.net>
> Subject: Re: [CR] Dawes Red Feather bike
> To: Peter Brueggeman <4peebee@peterbrueggeman.com>,
> <haxixe@gmail.com>, Steve Whitting <ciocc_cat@yahoo.com>
> Cc: classicrendezvous@bikelist.org
> Message-ID: <350510.87791.qm@web82208.mail.mud.yahoo.com>
> Content-Type: text/plain; charset="iso-8859-1"
>
> As you say, a triple, or even a very wide range double, can drop a
> chain, although this is seldom a problem with an experienced
> tourist. On a wide range front setup one is most likely to drop
> the chain when shifting to the smallest ring. The same is probably
> true of all front setups. One can of course drop the chain outside
> the largest ring, but that is usually due to an incorrectly set FD
> outer stop sdjustment. And one can sometimes drop the chain
> between rings, but that is usually because the spacing between
> rings is too large or because of really poor shifting technique.
>
> The tendency to drop the chain when shifting to the smallest ring
> can be caused but an incorrectly adjusted inner stop, but even if
> the adjustment is correct,one can drop the chain, especially, as
> you say, when shifting quickly. It is my experience that this is
> due to causing too much momentary slack in the chain. A triple can
> be pretty slack on the inner ring/outer cog combo anyway, as even
> with a long cage RD there must often be a compromise between
> handling a large outer ring for downhills while not having the
> chain too slack on the small-small combo. This is made worse the
> wider the range is, so a 52-28 front will tend to have more slack
> than a 50-32. I think the problem dropping chains comes when one
> suddenly introduces slack when shifting to the smallest ring. Not
> only is the inner ring gear shifted to likely to have a somewhat
> slack chain, but the chain is momentarily much slacker yet, until
> the RD cage takes up the slack introduced by the
> front shift. With the momentarily excessive slack it is very easy
> for the chain to deflect enough to drop off inside the inner ring.
> And the faster you make the front shift, the less time the RD has
> to retension the chain.
>
> At my previous job in Texas, I had a mostly flat commute with one
> very steep climb. Approaching the climb I would usually be on the
> large ring and the middle cog or even one cog smaller. I would
> then shift to the smallest ring and largest cog for the climb. My
> normal tendency was to shift to the smallest ring first, then make
> the rear shift to the large cog. But doing this I experienced
> several dropped chains, including one that jammed between the crank
> and BB and proceeded to snap in half a perfectly good Campy Rally
> RD. The experience of destroying a rather expensive RD motivated
> me to analyze the problem. I came to the conclusion that by
> shifting to the smallest ring with the chain still on a middle to
> outer cog increased the extent of the momemtary slack in the chain,
> whereas if I shifted to the largest cog first, the tension on the
> chain would be higher when I started the front shift, and the chain
> would not become as slack during the shift.
> After adopting the technique of making the rear shift first, I
> don't think I dropped another chain.
>
> There are devices called "chain minders" or some such that clamp to
> the seat tube and provide a "lip" just inside the small ring to
> prevent the chain dropping. I have one of these but have never
> installed it, as it seems rather an admission of defeat that one
> cannot solve the problem with proper equipment adjustment and
> shifting technique.
>
> Regards,
>
> Jerry Moos
> Tuscaloosa, Alabama, USA
>
Jon Spangler Writer/editor Linda Hudson Writing
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