Chain length rule-of-thumb?

[PATRICK MOORE]

I just put a new Sachs P 48 (? Cheap, 8 speed, NIB) on the Fargo and
found that it is fully two links shorter than the 9 sp chain it
replaced. It will cover the Big/Big combo (46/34 -- note that the 34
is in the #7 position) without grumbling but the cage is angled
considerably forward. The next-to-biggest cog is a 28, I think, and it
handles that fine.

No chain suck on todays mixed dirt/pavement 26 mile ride, so perhaps
the added tension is helping keep things in place?

At any rate, given the above -- and the fact that I never use the
46/34 anyway; I do use the 46/28 occasionally -- any reason to think
that I ought to add more links?

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-------------------------
Patrick Moore, Albuquerque, NM, USA
For professional resumes, contact Patrick Moore, ACRW
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[dougP]

Patrick:

Sheldon has a chain length procedure involving running the chain over
the big & big combo but not thru the RD, plus a link or 2. Check it
out as it's been a while since I looked.

OTH, if it works, why mess with it? Sure, the RD is going to angled
out pretty good in the big & big but it still worked? I'd say "no
worries". I've used plenty of chains right out of the box that worked
fine. I've done Sheldon's procedure. Honestly can't say I see any
difference, and I've got a wide range cassette & triple on the
Atlantis.

dougP

On Oct 19, 2:24 pm, PATRICK MOORE <bertin...@gmail.com> wrote:
> I just put a new Sachs P 48 (? Cheap, 8 speed, NIB) on the Fargo and
> found that it is fully two links shorter than the 9 sp chain it
> replaced. It will cover the Big/Big combo (46/34 -- note that the 34
> is in the #7 position) without grumbling but the cage is angled
> considerably forward. The next-to-biggest cog is a 28, I think, and it
> handles that fine.
>
> No chain suck on todays mixed dirt/pavement 26 mile ride, so perhaps
> the added tension is helping keep things in place?
>
> At any rate, given the above -- and the fact that I never use the
> 46/34 anyway; I do use the 46/28 occasionally -- any reason to think
> that I ought to add more links?
>
> --

> Vote early, vote often, vote Rhinoceros!http://tinyurl.com/d7muj2t

[Andy Smitty Schmidt]

Interesting question. 

I've been doing my own wrenching for many years and chain length (on derailer bikes) is one of those things that's always been eluded me. My experience is that there seems to be some "wiggle room". I tend to error on making the chain as short as possible so that everything still works, but adding a link or 2 often still works fine too. I haven't read Sheldon's spiel on the subject.

--Andy

[Jeremy Till]

As long as it shifts smoothly into and out of the big/big combo (i.e., you can't feel any binding) you should be good.  Cage angle doesn't make much of a difference.  

I use the big-big + 1 complete link (i.e. one whole set of inner and outer plates) rule of thumb and it's served me well.  The caveat i would add is that "big big" means the minimum amount of chain that would go over both cogs and still *easily* close--i.e. it wouldn't be a stretch to connect.  Then add one complete link and cut from there. 

On Friday, October 19, 2012 2:24:56 PM UTC-7, Patrick Moore wrote:

[PATRICK MOORE]

Thanks Doug, Andy and Jeremy. The new and shorter chain didn't "suck"
during its first ride, including dusty dirt, which is an improvement
over the previous, longer chain which was starting to "suck" more
frequently. As I said, there is no binding or grumbling when shifting
to the big/big, and there is still slack left in the rd on this
combination. Overall the system shifts very well with the new, shorter
chain.

I suppose my question was moved by a dim, unreflective supposition
that more slack means less tension, and that less tension means less
friction and wear -- I am obviously in mind still back in the 1950s
with those French racing derailleurs that allowed you to adjust rear
derailleur spring tension manually.

Multispeed bikes are so *complicated*, aren't they?

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[Kerry Kunsman]

First, you always want to make sure you can reach the big-ring,
big-sprocket combo. You might not ever use it (and you shouldn't),
but if you accidentally shift into it (sudden red light as your
cruising along in the big ring) and you can't reach it, you might
destroy your rear derailer. That being said, Sheldon's site has good
advice. I have always used the method of, with the chain threaded
normally, carefully shifting to the big-big combo, then check that
you could remove one link pair when the derailer is fully
extended. You need this little bit of slack so the chain can ride up
and onto the big ring before settling onto it. More slack is OK as
long as the derailer can take up the slack. Even if it can't, you
may get chain suck and skipping, and you'll definitely hear a lot of
complaining from your drivetrain, but ay least you won't permanently
destroy things.

Kerry Kunsman
San Diego, CA

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[rw1911]

I've always found the Park Tool site to be useful...

http://www.parktool.com/blog/repair-help/chain-length-sizing

On Oct 19, 5:24 pm, PATRICK MOORE <bertin...@gmail.com> wrote:
> I just put a new Sachs P 48 (? Cheap, 8 speed, NIB) on the Fargo and
> found that it is fully two links shorter than the 9 sp chain it
> replaced. It will cover the Big/Big combo (46/34 -- note that the 34
> is in the #7 position) without grumbling but the cage is angled
> considerably forward. The next-to-biggest cog is a 28, I think, and it
> handles that fine.
>
> No chain suck on todays mixed dirt/pavement 26 mile ride, so perhaps
> the added tension is helping keep things in place?
>
> At any rate, given the above -- and the fact that I never use the
> 46/34 anyway; I do use the 46/28 occasionally -- any reason to think
> that I ought to add more links?
>
> --

> Vote early, vote often, vote Rhinoceros!http://tinyurl.com/d7muj2t

[Kerry Kunsman]

That method would not work for me.  My drivetrain is configured for an extended range and there is no way even a long cage derailer can wrap enough chain to go from big-big to little-little.  In my granny gear I can only use the lowest (biggest) 4 cogs until the chain goes slack.  That's OK, since I don't use the higher gears in the granny anyway. If I do forget to shift up to the middle ring soon enough I'm reminded by a lot of chain noise and skipping, but no permanent harm.  If I didn't configure the chain this way then I couldn't reach the big-big combo, and as I mentioned in an earlier post, the results of not being able to do that could be disastrous.

Kerry Kunsman
San Diego, CA

At 04:14 PM 10/22/2012, Tom M wrote:

Nick Legan, formerly of VeloNews, approaches it differently ( http://velonews.competitor.com/2011/11/bikes-and-tech/ask-nick/ask-nick-team-tactics-chain-lengths-choosing-a-new-bike-and-more_197660 ):

Here�s my chain sizing method for a road bike (with entirely compatible gearing and derailleurs). I recommend sizing your chain using the largest cogset you intend to ride.

-Run the chain through the rear derailleur, on the smallest cog and on the small chainring. Pull it to where the chain won�t touch the pulley cage of the rear derailleur, keeping it as long as possible.

-If you�re cautious, mark the pivot that you intend to cut with a Sharpie, then run the chain (still through the derailleur) over the biggest cog and big chainring. You should have plenty of slack.

On Saturday, October 20, 2012 3:17:47 AM UTC-4, rw1911 wrote:

I've always found the Park Tool site to be useful...

http://www.parktool.com/blog/repair-help/chain-length-sizing

On Oct 19, 5:24 pm, PATRICK MOORE <bertin...@gmail.com> wrote:

> I just put a new Sachs P 48 (? Cheap, 8 speed, NIB) on the Fargo and

> found that it is fully two links shorter than the 9 sp chain it

> replaced. It will cover the Big/Big combo (46/34 -- note that the 34

> is in the #7 position) without grumbling but the cage is angled

> considerably forward. The next-to-biggest cog is a 28, I think, and it

> handles that fine.

>

> No chain suck on todays mixed dirt/pavement 26 mile ride, so perhaps

> the added tension is helping keep things in place?

>

> At any rate, given the above -- and the fact that I never use the

> 46/34 anyway; I do use the 46/28 occasionally -- any reason to think

> that I ought to add more links?

>

> --

> Vote early, vote often, vote Rhinoceros! http://tinyurl.com/d7muj2t

>

> -------------------------

> Patrick Moore, Albuquerque, NM, USA

> For professional resumes, contact Patrick Moore, ACRWhttp:// resumespecialties.com/index.html

> -------------------------

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[PATRICK MOORE]

I once set up a mountain bike (one of those bikes I wish I had kept:
'91 Specialized Stumpjumper Team; wonderful frame) with a 48/38/24
14-34 7 speed drivetrain using a 8 speed era Ultegra (= short cage)
rd. It worked fine, tho' it would grumble climbing onto the 34 when it
was covered in sand. I simply let the chain dangle in the granny: the
Ultegra would hold the chain fine on the two (or so) largest cogs, but
beyond those, the chain would sag on the bottom rung like Jean Robic's
with the Simplex 543 as he tried to keep up with Coppi.

I never had any problems on the few occasions that I shifted into
something smaller than the 28.

[lungimsam]

Rivendell's method at 3:44 in this video:

 

http://www.youtube.com/watch?v=gpPz8K4laFE