Chain Length
#1
Member
Thread Starter
Join Date: Jan 2010
Location: Bradenton, FL
Posts: 41
Bikes: Bianchi Volpe, Trek HiFi Deluxe
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 3 Post(s)
Likes: 0
Liked 4 Times
in
1 Post
Chain Length
I'm replacing my 12-23 cassette with a more touring friendly 11-32. How do figure the correct chain length?
#2
working on my sandal tan
Join Date: Aug 2011
Location: CID
Posts: 22,627
Bikes: 1991 Bianchi Eros, 1964 Armstrong, 1988 Diamondback Ascent, 1988 Bianchi Premio, 1987 Bianchi Sport SX, 1980s Raleigh mixte (hers), All-City Space Horse (hers)
Mentioned: 98 Post(s)
Tagged: 0 Thread(s)
Quoted: 3870 Post(s)
Liked 2,563 Times
in
1,577 Posts
To find the minimum chain length, loop the chain around the big chainring and 32T cog -- bypassing the rear derailleur -- and add 1". The whole system may be happier with a slightly longer chain, so if you have a reusable master link, you might start out with a chain that is a couple links longer than the above formula and see how the rear derailleur responds when you're in the small-small combination. (If the chain is too long, the lower derailleur pulley will swing up all the way, and parts will start bouncing and rubbing on each other -- not good.)
#3
MUP World Champ
Here is a chain length calculator to get you started: https://www.machinehead-software.co.u...engthcalc.html
#4
Member
Thread Starter
Join Date: Jan 2010
Location: Bradenton, FL
Posts: 41
Bikes: Bianchi Volpe, Trek HiFi Deluxe
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 3 Post(s)
Likes: 0
Liked 4 Times
in
1 Post
Awesome. Thanks!
This is the first cassette swap I've done and just realized that I've never had to figure this out before. I've always had an old chain to base the new one off.
This is the first cassette swap I've done and just realized that I've never had to figure this out before. I've always had an old chain to base the new one off.
#5
Senior Member
Join Date: Apr 2009
Location: New Rochelle, NY
Posts: 38,663
Bikes: too many bikes from 1967 10s (5x2)Frejus to a Sumitomo Ti/Chorus aluminum 10s (10x2), plus one non-susp mtn bike I use as my commuter
Mentioned: 140 Post(s)
Tagged: 1 Thread(s)
Quoted: 5766 Post(s)
Liked 2,538 Times
in
1,404 Posts
There are 3 ways.
The shortest chain method is to loop the chain around the big front/big rear, and add 1". This has zero fudge room, and represents the absolute minimum safe length you an use.
If the RD has enough capacity you can use a longer chain, measured by the small/small combination and shortened until the RD cage can take up all the slack.
If there's enough capacity, Shimano suggests a length between these, based on the angle of the cage in a certain combination.
I prefer to use a longer chain, so I have the capacity to cut out a link in case I ever have to. But I always start by confirming that it's long enough via the big/big method.
One other note -- if you have a road bike with a 12-23 cassette originally, you'll almost definitely need a longer chain, but you may also not have enough take up capacity if it has a short cage RD. Here you have a choice. You can buy a new long cage RD, or if it's only slightly under capacity, can use the shortest chain possible, and avoid the small/smaller combinations (rarely used anyway) where the RD can't take up the slack.
The shortest chain method is to loop the chain around the big front/big rear, and add 1". This has zero fudge room, and represents the absolute minimum safe length you an use.
If the RD has enough capacity you can use a longer chain, measured by the small/small combination and shortened until the RD cage can take up all the slack.
If there's enough capacity, Shimano suggests a length between these, based on the angle of the cage in a certain combination.
I prefer to use a longer chain, so I have the capacity to cut out a link in case I ever have to. But I always start by confirming that it's long enough via the big/big method.
One other note -- if you have a road bike with a 12-23 cassette originally, you'll almost definitely need a longer chain, but you may also not have enough take up capacity if it has a short cage RD. Here you have a choice. You can buy a new long cage RD, or if it's only slightly under capacity, can use the shortest chain possible, and avoid the small/smaller combinations (rarely used anyway) where the RD can't take up the slack.
__________________
FB
Chain-L site
An ounce of diagnosis is worth a pound of cure.
Just because I'm tired of arguing, doesn't mean you're right.
“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN
WARNING, I'm from New York. Thin skinned people should maintain safe distance.
FB
Chain-L site
An ounce of diagnosis is worth a pound of cure.
Just because I'm tired of arguing, doesn't mean you're right.
“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN
WARNING, I'm from New York. Thin skinned people should maintain safe distance.
Last edited by FBinNY; 10-23-12 at 12:24 PM.
#6
Senior Member
Join Date: Sep 2010
Location: Roswell, GA
Posts: 8,319
Bikes: '93 Trek 750, '92 Schwinn Crisscross, '93 Mongoose Alta
Mentioned: 30 Post(s)
Tagged: 0 Thread(s)
Quoted: 1438 Post(s)
Liked 1,092 Times
in
723 Posts
Besides the "chain take-up" capacity you will also need to consider the "largest rear cog" capacity of the derailleur you have. Some road type derailleurs will only accomodate a 28- or 30-tooth large cog; the jockey wheel may not have enough clearance from the 32-tooth cassette if this is the case. This capacity will specified be in the manufacturer's tech documents. Depending on the bike this capacity may be exceeded by a few teeth but you will need to try it and see.