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Will changing cassette effect chain length

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Will changing cassette effect chain length

Old 02-15-15, 03:49 AM
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Will changing cassette effect chain length

I have a Domane with 10 speed Tiagra (triple) groupset. It is time for me to change the chain and I was considering on changing the rear cassette due to the area I ride in. I was hoping to install a Shimano 105 with 11-28 gears along with a Shimano 105 chain. My current rear Tiagra set up is a 12-30. I know the tools I would need but I was trying to figure out how I would set the chain up for 11-28 gears. Any help would be greatly appreciated.
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Old 02-15-15, 04:00 AM
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The difference is only 1 link shorter (diff between 12 & 11), no need to do anything. But just a comment, the difference between those two cassettes is small. You might consider an 11-25 for smaller steps between gears, using the 11-25 for flatter rides and the 12-30 for hills Depends on the terrain where you live of course.
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Old 02-15-15, 04:33 AM
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Two links shorter (28-30). You go by the largest cog size, not the smallest.

Park Tool Co. » ParkTool Blog » Chain Length Sizing
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Old 02-15-15, 04:41 AM
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Originally Posted by Lazyass
Two links shorter (28-30). You go by the largest cog size, not the smallest.

Park Tool Co. » ParkTool Blog » Chain Length Sizing
If you need to lengthen the chain you would go by the large-large combination. If you need to shorten the chain you would of course consider smallest-smallest, and since most cyclists have multiple cassettes, you only consider if you are outside the range of what the derailleur will handle, and in this case it would be IF the chain is already on the border of being too long, and one link would put it over the edge.
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Old 02-15-15, 04:56 AM
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Originally Posted by kingfishr
If you need to lengthen the chain you would go by the large-large combination. If you need to shorten the chain you would of course consider smallest-smallest, and since most cyclists have multiple cassettes, you only consider if you are outside the range of what the derailleur will handle, and in this case it would be IF the chain is already on the border of being too long, and one link would put it over the edge.

That's incorrect. Chain length is always measured in the big/big. If it's too short you can destroy the rear derailleur shifting into the large sprocket. Not something I would roll the dice on. And I've never seen a chain length calculator that asks for the small cog size. I don't think the average cyclist has multiple sized cassettes that they're switching back and forth, but if so all they need to do is add or remove links during installation.
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Old 02-15-15, 05:54 AM
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Originally Posted by Lazyass
That's incorrect. Chain length is always measured in the big/big. If it's too short you can destroy the rear derailleur shifting into the large sprocket. Not something I would roll the dice on. And I've never seen a chain length calculator that asks for the small cog size. I don't think the average cyclist has multiple sized cassettes that they're switching back and forth, but if so all they need to do is add or remove links during installation.
Strange because even the link you provided says to check small-small:

"Shift bike to smallest chainring in front and smallest cog in back. Inspect the section of chain between lower derailleur pulley wheel and bottom of smallest chainring. There should not be an obvious sag in the chain. Check also that the lower section of chain does not rub chain at upper pulley. It is normal for there be low chain tension in this position, but the chain should not sag. Sagging in this position indicates a chain that is too long."

in the OP's question he is going from a 30 to a 28 tooth max so there is no risk that the chain is going to be too short.
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Old 02-15-15, 06:09 AM
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Good question and discussion. Big picture I don't think a link or two one way or another will matter, but I honestly don't know what the "truth" is.

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Old 02-15-15, 07:29 AM
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This is what SRAM recommends (clipped from their 2015 cassettes & chains tech doc):



The PowerLink is then used to tie the chain together.

Always works for me.
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Old 02-15-15, 10:16 AM
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What I've learned with help from many on the mechanics forum is a good amount of room for error as long as the chain is too long and not too short. I went from standard 53/39 cranks to compact without touching my chain and have had no problems. But if you plan on swapping cassette and chain why is this a question? Swap the cassette and size the new chain appropriately.
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Old 02-15-15, 10:35 AM
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When changing cassettes, you need to take more than one thing into consideration. If the largest rear cog is smaller, no problem. If the smallest rear cog is no smaller, no problem. If the smallest rear cog is smaller, you have to take into consideration whether the derailleur can take up the extra chain. Likewise, if the largest rear cog is larger, you need to know if the derailler is capable of utilizing that big gear, and if you have enough chain to function.

Lots more than just worrying about the big/big.
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Old 02-15-15, 02:28 PM
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This is what happens when a chain is not long enough to run Big Big.

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Old 02-16-15, 09:18 AM
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All this applied to the OP's situation.

The existing chain length will be fine. The big big combination is 2 fewer links, so the chain is long enough.

The small small is one link smaller, so there's one more link for the derailleur to wrap, but it should easily have the capacity for that.

Theoretically, you could run the chain two links shorter, but it would make sense to keep the same lenght you have if you want to put the 12-30 back on at some point.
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Old 02-16-15, 09:36 AM
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I've sized chains both using big-big and small-small. My question is: How different is the final chain length using the two methods? It would be funny if with all this hand-wringing they yield the same result.
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Old 02-16-15, 09:42 AM
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Originally Posted by dstrong
I've sized chains both using big-big and small-small. My question is: How different is the final chain length using the two methods? It would be funny if with all this hand-wringing they yield the same result.
The answer is "it depends". Small-small on an 11-xx will always result in the same size. Big-big on an 11-23, 11-25, 11-28, and 11-30 will all result in different lengths. Which one if any will be the same as small-small? Who knows.

You can definitely say if big-big sizing results in a chain too long for small-small, and small-small sizing results in a chain to short for big-big, then you have the wrong rear derailleur for your drivetrain.

I use the small-small method so that I don't need to keep different chains for different cassettes.
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