In article <
[email protected]>,
"* * Chas" <
[email protected]> wrote:
> "TBerk" <[email protected]> wrote in message
> news:41ea924f-4d02-44a5-b103-ae889737cf4f@i36g2000prf.googlegroups.com...
> > I was popping around looking at some different sites and I found this
> > thing:
> >
> > 3rd Eye Chain Watcher
> >
> > * 3rd Eye Chain Watcher Chain Deflector
> > * Prevents granny gear from overshifting
> > * Fits 1-1/8" to 1-3/8" round or oval seat tubes
> >
> > What exactly is overshifting? (I'm going to make sure my guesses of
> > what the granny gear is on my own.)
> >
> > What does this thing do, if anything?
> >
> >
> > Thx in advance,
> > TBerk
>
> This and several other similar devices are designed to keep the chain from
> falling off of the small inner chainring when down shifting or bouncing on
> rough surfaces.
>
> They can help prevent "chain suck" where the chain gets caught between the
> crank and chainstays or bottom bracket.
I suppose they could help with chain suck, but that's usually defined as
what happens when the chain fails to disengage from the ring(s) at the
bottom of the ring and there's a separate device for preventing it:
http://www.bikepro.com/products/chains/chainretainer.html
Behold the Ringle Anti Chain Suck Thing.
The difference is simple to remember:
chain drop = cranks spin freely = bike stops, rider falls down
chain suck = cranks lock = bike stops, rider falls down
So basically, if your crotch hits the seat or top tube, it's chain drop,
while if your crotch hits the back of the stem, it's chain suck.
Chain suck is fairly rare outside of mountain biking circles but chain
drop appears in more circumstance. A chain watcher is a reasonable
device for any rider on rough roads, though I'd be reluctant to call it
necessary. I purely forgot to put my old chain watcher on my new CX bike
last year, and I think I actually did drop my chain off the small ring
(compact double setup; letters from purists to the usual address) once
or twice during races.
Cyclocross bikes are somewhat prone to chain drop during dismounts,
remounts, and just as a result of rough and mucky terrain.
--
Ryan Cousineau
[email protected] http://www.wiredcola.com/
"In other newsgroups, they killfile trolls."
"In rec.bicycles.racing, we coach them."