Chain slaps chainstay?

DougA wrote:
> I had all my parts swapped to a new frame at my LBS. The chain now slaps
> the chainstay over big pumps. I have a Record med cage RD and a 13-26
> cassette. The LBS took a link out of the chain and said if that didn't work
> I would need to buy a short cage RD. The link removal helped but it still
> slaps.

You never can avoid that completely especially when you are in the small
ring. When your chain is on the big ring this should not happen.
Get a chainstay protector.

>
> Do I need a short cage RD? They also said a short cage RD will shift
> better. True?

Yes a couple of nanoseconds.

Lou
--
Posted by news://news.nb.nu (http://www.nb.nu)

DougA wrote:
> I had all my parts swapped to a new frame at my LBS. The chain now slaps
> the chainstay over big pumps. I have a Record med cage RD and a 13-26
> cassette. The LBS took a link out of the chain and said if that didn't work
> I would need to buy a short cage RD. The link removal helped but it still
> slaps.
> Do I need a short cage RD? They also said a short cage RD will shift
> better. True?


With a 39-53 front and a Record 72mm cage with 26t low rear you should
indeed not have chain sag.

Your assembler should have wrapped the chain around largest rear and
largest front, then counted 2 more rivets, then passed it through the
changers, then reconnected your snap link. Merely adding or subtracting
links intuitively isn't best practice (although sometimes the result may
be identical). It's nice to know with certainty that nothing will break
on a cross gear shift.

Check the tension screw setting, which may vary from frame to frame
depending on geometry of the frame's gear tab.

Short cages obviously do not have as much capacity as medium cages so
whatever chain sag symptoms you have now will be no better with a
smaller changer. Might be no worse, though. Shift response isn't
noticeably different between Record medium and long changers, IMHO, both
are excellent.

Something unstated isn't right I agree. Chain sag is not normal to that
equipment selection.
--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971

I forgot to mention in the OP that the front is a CT 50-34 and the slap
occurs during bumps riding 50 front and middle in the back.

"A Muzi" <[email protected]> wrote in message
news:[email protected]...
> DougA wrote:
>> I had all my parts swapped to a new frame at my LBS. The chain now slaps
>> the chainstay over big pumps. I have a Record med cage RD and a 13-26
>> cassette. The LBS took a link out of the chain and said if that didn't
>> work I would need to buy a short cage RD. The link removal helped but it
>> still slaps.
>> Do I need a short cage RD? They also said a short cage RD will shift
>> better. True?
>
>
> With a 39-53 front and a Record 72mm cage with 26t low rear you should
> indeed not have chain sag.
>
> Your assembler should have wrapped the chain around largest rear and
> largest front, then counted 2 more rivets, then passed it through the
> changers, then reconnected your snap link. Merely adding or subtracting
> links intuitively isn't best practice (although sometimes the result may
> be identical). It's nice to know with certainty that nothing will break on
> a cross gear shift.
>
> Check the tension screw setting, which may vary from frame to frame
> depending on geometry of the frame's gear tab.
>
> Short cages obviously do not have as much capacity as medium cages so
> whatever chain sag symptoms you have now will be no better with a smaller
> changer. Might be no worse, though. Shift response isn't noticeably
> different between Record medium and long changers, IMHO, both are
> excellent.
>
> Something unstated isn't right I agree. Chain sag is not normal to that
> equipment selection.
> --
> Andrew Muzi
> www.yellowjersey.org
> Open every day since 1 April, 1971

DougA wrote:
> I forgot to mention in the OP that the front is a CT 50-34 and the slap
> occurs during bumps riding 50 front and middle in the back.

Convert it to a fixed gear. Not only will this totally eliminate
chainstay slap, it will make you instantly irresistible to the opposite
sex (or the same sex, if that's what floats your boat).

Something's wrong. Check if the chain is sticking to the cog as it
goes over the top, or if the derailleur cage is sticking in it's wind
up. There's no way this combo should be slapping unless you have a
really wierd resonance...

JG

On Aug 25, 4:32 pm, "DougA" <[email protected]> wrote:
> I forgot to mention in the OP that the front is a CT 50-34 and the slap
> occurs during bumps riding 50 front and middle in the back.
>
> "A Muzi" <[email protected]> wrote in message
>
> news:[email protected]...
>
> > DougA wrote:
> >> I had all my parts swapped to a new frame at my LBS. The chain now slaps
> >> the chainstay over big pumps. I have a Record med cage RD and a 13-26
> >> cassette. The LBS took a link out of the chain and said if that didn't
> >> work I would need to buy a short cage RD. The link removal helped but it
> >> still slaps.
> >> Do I need a short cage RD? They also said a short cage RD will shift
> >> better. True?

Not true and the bike shop needs to get a clue. On normal 2 ring
setups, medium and long cage rear derailleurs, altho not 'needed',
work fine. For these guys to suggest that you may 'need' a short cage
is pitiful. Short cage rear derailleiurs don't shift any better than
medium or long. The chain length is probably too long is all..


>
> > With a 39-53 front and a Record 72mm cage with 26t low rear you should
> > indeed not have chain sag.
>
> > Your assembler should have wrapped the chain around largest rear and
> > largest front, then counted 2 more rivets, then passed it through the
> > changers, then reconnected your snap link. Merely adding or subtracting
> > links intuitively isn't best practice (although sometimes the result may
> > be identical). It's nice to know with certainty that nothing will break on
> > a cross gear shift.
>
> > Check the tension screw setting, which may vary from frame to frame
> > depending on geometry of the frame's gear tab.
>
> > Short cages obviously do not have as much capacity as medium cages so
> > whatever chain sag symptoms you have now will be no better with a smaller
> > changer. Might be no worse, though. Shift response isn't noticeably
> > different between Record medium and long changers, IMHO, both are
> > excellent.
>
> > Something unstated isn't right I agree. Chain sag is not normal to that
> > equipment selection.
> > --
> > Andrew Muzi
> >www.yellowjersey.org
> > Open every day since 1 April, 1971