Chain Capacity Issue - What's Your Opinion

Discuss light weight issues concerning road bikes & parts.
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Catagory6
Posts: 399
Joined: Thu Feb 09, 2017 2:36 am

by Catagory6

i am going to run a cassette which has sprockets slightly beyond the capabilities of the rear derailleur, along with the chain rings i'm using.

these facts are immutable. what's done is done. i've signed the contract in my own blood, and put up my soul as collateral.

here's the question for you:

do you size the chain so that the RD can safely shift into big-sprocket/big-chainring, and have excess chain sagging in the small/small combo?

or, do you size the chain for proper small/small specifications, and pay extra special attention when slogging through the mud, blood, sweat and beer to never shift into the big/big combo?

my feeling is the first setup, for the most obvious reason of not having to worry about ripping out a RD and hanger. what are your professional opinions?

mattr
Posts: 4673
Joined: Fri May 25, 2007 6:43 pm
Location: The Grim North.

by mattr

You are far more likely to accidentally go into Big Big than Small Small.

The consequences are also far more serious, clattering noise of a too long chain Vs the horrendous crack of a rear mech launching itself off the dropout into the rear wheel, under load.

Size it for Big Big.

BTW, if it's shimano they are notoriously stingy with capacities, i've run systems well outside the official spec that have worked flawlessly for extended periods.

by Weenie


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Lewn777
Posts: 832
Joined: Thu Mar 09, 2017 5:35 am

by Lewn777

big--big +1
Often Shimano can comfortably go much bigger, some long cages can comfortably go to 36 like Tiagra other 11speed a bit less, some people use a wolf tooth extender, but I find they make shifting poorer.
Ideally change your front sprokets to a smaller size rather than screwing about at the back end, because it can be sensitive to change.
I love my SRAM stuff but I wouldn't trust it outside of manufacturer approved tolerances.

Catagory6
Posts: 399
Joined: Thu Feb 09, 2017 2:36 am

by Catagory6

Campy, and i've already measured out the chain length for both combos, and its outside campy's stingy specs as well.
its a 12-32, 34/50 and small-cage RD

thanks for the confirmation

mattr
Posts: 4673
Joined: Fri May 25, 2007 6:43 pm
Location: The Grim North.

by mattr

There have been a couple of threads on out of spec campag set ups lately. Might be worth having a look at them.
And changing the thread title so you get some more hits.

alcatraz
Posts: 2202
Joined: Mon Aug 29, 2016 11:19 am

by alcatraz

Depends on what direction your cage is pointing in big-big. 5 o' clock is safe but if you are desperate you could (with some risk) push it to 4 o' clock.

You can also increase capacity by simply oversizing pulley wheels. This needs to be done before sizing the chain though.

I even undersized the upper pulley wheel to 10t and run a 16t bottom on a 36t medium cage setup. This way the B-screw can be a bit more relaxed (less strain) and you don't tension the chain like crazy in big/big which wll be noisy as hell.

Depending on the design of your derailleur cage you will be limited to 14t or in rare occasions 12t (short cage with tabs running closer to the wheels. Remember the chain and wheel needs to fit inside the tabs.

Running even toothed pulley wheels allows you to run wide/narrow tooth profiles. This helps shifting performance in the small cogs by reducing increased chain deflection that occurs with the larger pulley/cog distance there. You only benefit of wide/narrow profile on the upper pulley. Some have a break in period before they become silent. Stay away from cheap ceramic pulley wheels = huge chain deflection = crap shifting on big distance pulley/cog gears. Aluminum pulleys are noisier and heavier than plastic.

TobinHatesYou
Posts: 4160
Joined: Mon Jul 24, 2017 12:02 pm

by TobinHatesYou

Yep keep in mind the cage needs to bend more than when it's sitting happily in the big-big combo. When shifting to the big ring, the chain will briefly "float" above the teeth for example.

pooka
Posts: 5
Joined: Fri Feb 16, 2018 10:16 am

by pooka

I faced the same choice with an Ultegra 6800 groupset and R8000 medium cage derailleur, 50/34 rings paired with 11-32 cassette. If I cut the chain to allow big/big the chain slack was not just bad for small/small (the chain rubbed on the lower part of the upper pulley wheel) but I wasn't happy with it in the next gear up either (and possibly the next 2 gears up, I can't recall for sure now).

I went with the shorter chain. It was my wife's bike, so I made her aware of the risks, but you can obviously never rule out a moment of forgetfulness. She rides long distance, including multi-day events, the accumulated fatigue of such events adds to the risk of making a bad gearing choice, but after several months of use so far so good.

I'm not looking forwarded to revisiting this though when looking at a 11-34 cassette in the near future.

by Weenie


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