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?
Chain Capacity Issue - What's Your Opinion
Moderator: robbosmans
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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.
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.
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.
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.
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.
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.
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TobinHatesYou
- Posts: 12571
- Joined: Mon Jul 24, 2017 12:02 pm
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.
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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.
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.
