Chain Sizing and Cassette Question

Quoted message said:

I currently have a 9 Speed Dura Ace drivetrain with a 12-23 cassette
and a 53-39 chainring. I have just purchased a 12-27 cassette
I have also purchased a chain to go with the new cassette.

I have done a bit of research on chain sizing and installation using
the Park Tools and Sheldon Brown websites and the Shimano service
instructions, but I would like some advice from a.b'ers. I realise
there are a lot of different variables here,

No there aren't! There are only 3 variables:

·Biggest chainring size

·Biggest rear sprocket size

·Chainstay length

Quoted message said:

i) Since my current cassette is a 12-23 and I want to put a 12-27
cassette in, I assume my existing chain will not be long enough to
handle the larger cog with 27 teeth.

That's likely correct.

Quoted message said:

The previous owner of the bike
knows more about bikes than I do so I assume the chain length has been
optimised for a 12-23. OK, no problems so far, I will just calculate
the required length based on the equation given on the Park Tools
website.

It's silly to calculate chain length with an equation, just cut it to
fit, as explained at:

http://sheldonbrown.com/derailer-adjustment

Quoted message said:

However, since I might want to swap between cassettes on a regular
basis (the 12-23 will be used for crits, the 12-27 will be used for
hills and training), won't this mean I will have to regularly have to
swap chains by breaking them and reconnecting them using the special
Shimano reinforced connecting pins?

No, the longer chain will work fine with the smaller cassette too.

Quoted message said:

ii) The service instruction sheet for the DA-7700 rear derailleur
states that the largest sprocket size it can accomodate is 26. A bit of
Googling reveals that Shimano tends to understate the maximum
accomodated sprocket size.

Yes. This is explained in detail at:

http://sheldonbrown.com/capacity

Quoted message said:

Has any one here used a 7700 rear derailleur with a 12-27 cassette?

Thousands of people do this.

I haven't used the 12-27, but I have used 12-28 on one of my bikes with
that derailer. Worked fine.

We also sell lots of 13-30 cassettes for these installations. It
varies somewhat with the frame's specific dropout geometry, but it
almost always works. 30 seems to be about the practical limit for this
derailer.

Quoted message said:

iii) Is there anything else I might need to do once I install the new
cassette and chain, e.g. derailleur adjustments?

It's all explained at http://sheldonbrown.com/derailer-adjustment

Sheldon "Easier Than You Might Imagine" Brown
+-------------------------------------------------------------+
| Give a man a fire, and he will stay warm for a day. |
| Set a man on fire, he stays warm for the rest of his life. |
+-------------------------------------------------------------+
Harris Cyclery, West Newton, Massachusetts É-U
Télephone 617-244-9772 FAX 617-244-1041
http://sheldonbrown.com/french/harris
les pièces "introuvables" envoyé dans le monde entire

[email hidden said:

"]Hi all,

I currently have a 9 Speed Dura Ace drivetrain with a 12-23 cassette
and a 53-39 chainring. I have just purchased a 12-27 Ultegra 9 speed
cassette because a 12-23 isn't going to do me any favours on hills
(though I managed to do the ride up from the Bobbin Head marina along
Bobbin Head Road in Sydney on a 12-23). I have also purchased a Dura
Ace CN-7701 chain to go with the new cassette.

I have done a bit of research on chain sizing and installation using
the Park Tools and Sheldon Brown websites and the Shimano service
instructions, but I would like some advice from a.b'ers. I realise
there are a lot of different variables here, so I'll try to give as
much info as possible.

So, the questions are ...

i) Since my current cassette is a 12-23 and I want to put a 12-27
cassette in, I assume my existing chain will not be long enough to
handle the larger cog with 27 teeth. The previous owner of the bike
knows more about bikes than I do so I assume the chain length has been
optimised for a 12-23. OK, no problems so far, I will just calculate
the required length based on the equation given on the Park Tools
website.

However, since I might want to swap between cassettes on a regular
basis (the 12-23 will be used for crits, the 12-27 will be used for
hills and training), won't this mean I will have to regularly have to
swap chains by breaking them and reconnecting them using the special
Shimano reinforced connecting pins? This sounds like a real pain to do
(and I will have to keep a large enough supply of special connecting
pins). Is there a "halfway point" for the chainlength so that it can
accomodate both a 12-23 and 12-27 cassette? I realise this might mean I
have to be careful not to use the small-small and big-big gear
combinations.

ii) The service instruction sheet for the DA-7700 rear derailleur
states that the largest sprocket size it can accomodate is 26. A bit of
Googling reveals that Shimano tends to understate the maximum
accomodated sprocket size. Has any one here used a 7700 rear
derailleur with a 12-27 cassette?

iii) Is there anything else I might need to do once I install the new
cassette and chain, e.g. derailleur adjustments?

Thanks in advance. Once I get the cassette and chain installed, it will
be time to look at wheels ...

It should be fine. I've done this with 9 speed ultegra. You don't need a formula to calc chain length, just run the chain around the big ring and largest gear on the back without running the chain through the derailleur. Line up the two ends on the chain ring so there is no slack and positioned correctly so that you could put a joining link in, and then add one link. www.sheldonbrown.com has an article on this I think.

You will have a little bit of slack in the small chainring small rear gear combo but that is ok. The derailleur will handle it, just make sure it's not going to be too tight in the big/big combo.

Adam

Sheldon Brown wrote

Quoted message said:

Quoted message said:

The previous owner of the bike
knows more about bikes than I do so I assume the chain length has been
optimised for a 12-23. OK, no problems so far, I will just calculate
the required length based on the equation given on the Park Tools
website.

Quoted message said:

It's silly to calculate chain length with an equation, just cut it to
fit, as explained at:

Quoted message said:

http://sheldonbrown.com/derailer-adjustment

Thanks. I followed the instructions on that page to work out the chain
length.

Quoted message said:

Quoted message said:

However, since I might want to swap between cassettes on a regular
basis (the 12-23 will be used for crits, the 12-27 will be used for
hills and training), won't this mean I will have to regularly have to
swap chains by breaking them and reconnecting them using the special
Shimano reinforced connecting pins?

Quoted message said:

No, the longer chain will work fine with the smaller cassette too.

OK, that's good to hear.

Quoted message said:

Quoted message said:

Has any one here used a 7700 rear derailleur with a 12-27 cassette?

Quoted message said:

Thousands of people do this.

Quoted message said:

I haven't used the 12-27, but I have used 12-28 on one of my bikes with
that derailer. Worked fine.

Thanks. I managed to put the new cassette on the free hub (that was the
easy bit!) and installed a new chain. Unfortunately, I didn't make a
clean connection with the pin to join the chain (the pin wasn't
straight) and this led to the chain jumping when I was in a certain
cog.

I had to break the offending link but stuffed it up by pushing the pin
all the way out. OK, no problems so far, just put in another link with
a pin.

Unfortunately, the newly attached pin made the link very stiff and I
had to leave it at that since it was way past 1 a.m. I'll give it
another go later tonight.

Quoted message said:

Sheldon "Easier Than You Might Imagine" Brown

You are right, it was easier than I thought it was, apart from the
chain installation (I accept full responsibility my botched chain
installation).

adam85 wrote

Quoted message said:

It should be fine. I've done this with 9 speed ultegra. You don't need
a formula to calc chain length, just run the chain around the big ring
and largest gear on the back without running the chain through the
derailleur. Line up the two ends on the chain ring so there is no slack
and positioned correctly so that you could put a joining link in, and
then add one link. www.sheldonbrown.com has an article on this I
think.

Quoted message said:

You will have a little bit of slack in the small chainring small rear
gear combo but that is ok. The derailleur will handle it, just make
sure it's not going to be too tight in the big/big combo.

Thanks for pointing that out. Now I only have to fix the tight link in
my chain and put it together again and I'll finally have a decent gear
range to tackle some hills.

petulance said:

Thanks for pointing that out. Now I only have to fix the tight link in
my chain and put it together again and I'll finally have a decent gear
range to tackle some hills.

Avoid the pin problems by using wipperman chains which have a tool free joining link. We are using them on the 2 tandems and a couple of our other bike and find the wear and shift fine.

Cheers

Geoff