Chain length for dummies
#51
senior member
I have a favorites folder dedicated to cycling info and one of my favorite entries is a BF post with video on threading the cable to its' anchor on the Shimano FD-8000 - but for chain length I rely on Keith who has way more know how and experience than I - a few months back I felt that my shifting could be smoother and played around with cable tension , etc. but still fell short - dropped the bike off with Keith and when I picked it up there were 2 chain links attached by twist tie to the aero bar - should ask Keith what method he uses but if I were to pick a method I think it would be the one favored by Sheldon Brown .
#52
Mad bike riding scientist
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I'm curious if anyone has compared the different methods to see if the result differs?
Suddenly I can hardly wait for the next chain to stretch beyond spec!!! So far I think we have the following methods:
1. Match the number of links/full links/half links/rivets (whatever your nomenclature) of the old chain, which may have been sized by one of the following.
Suddenly I can hardly wait for the next chain to stretch beyond spec!!! So far I think we have the following methods:
1. Match the number of links/full links/half links/rivets (whatever your nomenclature) of the old chain, which may have been sized by one of the following.
2. Big-big plus two links/two half links/one full link/one inch/two rivets (again, whatever your nomenclature) with chain NOT routed through rear derailleur.
3. Small-small, chain routed through derailleurs, with enough tension on derailleur cage to take it off its maximum take up.
One caveat: The large/large method with the 46 and 48 tooth can result in a slack chain for the small/small combination.
4. Big chainring-small cassette cog, chain routed through derailleurs, rear derailleur cage pulled to vertical position.
5. Mathematical formula which I'm too lazy to recite and is my least favorite right now. So concrete. Where's the art?
I believe the caveat for at least some of these methods is that the largest cassette cog cannot be more than 36? And of course I have a number of RD manuals to read to see if Shimano has been consistent in their methods. I'm totally Shimano except for a couple of old Suntours. I wonder if they had manuals?
By the way, SRAM’s rear derailer manual provides the same advice as their chain manual does for sizing the chain.
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Stuart Black
Plan Epsilon Around Lake Michigan in the era of Covid
Old School…When It Wasn’t Ancient bikepacking
Gold Fever Three days of dirt in Colorado
Pokin' around the Poconos A cold ride around Lake Erie
Dinosaurs in Colorado A mountain bike guide to the Purgatory Canyon dinosaur trackway
Solo Without Pie. The search for pie in the Midwest.
Picking the Scablands. Washington and Oregon, 2005. Pie and spiders on the Columbia River!
#53
Mad bike riding scientist
Join Date: Nov 2004
Location: Denver, CO
Posts: 27,369
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Chain sizing isn't in the derailleur manuals? Then what's this? I especially like that part that is titled "Chain Length."
Dura Ace Rear Derailleur Manual
Dura Ace Rear Derailleur Manual
The CN-7700 instructions don't address chain length. That's what the RD-7700 manual linked above is for. Nowhere in that manual is there any mention big/big plus 2 rivets.
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Stuart Black
Plan Epsilon Around Lake Michigan in the era of Covid
Old School…When It Wasn’t Ancient bikepacking
Gold Fever Three days of dirt in Colorado
Pokin' around the Poconos A cold ride around Lake Erie
Dinosaurs in Colorado A mountain bike guide to the Purgatory Canyon dinosaur trackway
Solo Without Pie. The search for pie in the Midwest.
Picking the Scablands. Washington and Oregon, 2005. Pie and spiders on the Columbia River!
Stuart Black
Plan Epsilon Around Lake Michigan in the era of Covid
Old School…When It Wasn’t Ancient bikepacking
Gold Fever Three days of dirt in Colorado
Pokin' around the Poconos A cold ride around Lake Erie
Dinosaurs in Colorado A mountain bike guide to the Purgatory Canyon dinosaur trackway
Solo Without Pie. The search for pie in the Midwest.
Picking the Scablands. Washington and Oregon, 2005. Pie and spiders on the Columbia River!
#54
Full Member
Cyccommute: I looked up the manual for the XTR M972 and shimano recommended the big-big plus 2 back then: https://si.shimano.com/en/pdfs/si/5W...0B-001-ENG.pdf . But that was for mountain bikes. Shimano still recommends the big-small with derailleur cage vertical for newer road derailleurs up to certain max cog sizes (27 for double; 30 for triple): https://si.shimano.com/en/pdfs/dm/RD...003-09-ENG.pdf .
Likes For mitchmellow62:
#56
Newbie
Here are the criteria I start with:
A. The chain must be long enough for big/big with rear derailleur capacity to spare.
B. The chain should be short enough to maintain acceptable slop in small/small.
There may be multiple workable chain lengths that meet the two criteria above, depending on your combination of frame, rear derailleur, chainrings, and cogs. A longer chain weighs more, insignificantly extends drivetrain lifespan, and may enable swapping in a larger cog or chainring. A shorter chain weighs less, insignificantly reduces drivetrain lifespan, and may enable swapping in a smaller cog or chainring.
There are drivetrain configurations where the shortest possible chain for criteria A above will still be too long for criteria B. Avoid small/small selections in that case or revisit drivetrain component selection.
Last week I installed a new 12-36 cassette and new chain on my size 57 Jamis aurora touring bike with 26-36-48 crankset and mountain long cage derailleur. I installed the chain full length routed though the derailleur normally, carefully confirmed it worked in big/big, then checked for acceptable slop in small/small. It met both criteria so I left it uncut. 114 links.
Last time I sized a chain I used the big/big+2rivets park/sheldon method, and maybe if I was a bike mechanic in a hurry that's what I'd do, but since I have the time to screw around, I like my iterative approach.
A. The chain must be long enough for big/big with rear derailleur capacity to spare.
B. The chain should be short enough to maintain acceptable slop in small/small.
There may be multiple workable chain lengths that meet the two criteria above, depending on your combination of frame, rear derailleur, chainrings, and cogs. A longer chain weighs more, insignificantly extends drivetrain lifespan, and may enable swapping in a larger cog or chainring. A shorter chain weighs less, insignificantly reduces drivetrain lifespan, and may enable swapping in a smaller cog or chainring.
There are drivetrain configurations where the shortest possible chain for criteria A above will still be too long for criteria B. Avoid small/small selections in that case or revisit drivetrain component selection.
Last week I installed a new 12-36 cassette and new chain on my size 57 Jamis aurora touring bike with 26-36-48 crankset and mountain long cage derailleur. I installed the chain full length routed though the derailleur normally, carefully confirmed it worked in big/big, then checked for acceptable slop in small/small. It met both criteria so I left it uncut. 114 links.
Last time I sized a chain I used the big/big+2rivets park/sheldon method, and maybe if I was a bike mechanic in a hurry that's what I'd do, but since I have the time to screw around, I like my iterative approach.