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Changing Cassette Size Without Chaning Chain

Old 03-17-14, 08:07 AM
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flats
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Changing Cassette Size Without Chaning Chain

I'm about to put a new chain on my road bike. I have 50/34 chainrings and an 11-23 cassette. I like the 11-23 for racing but I'm planning to do some very steep climbing (sustained grades over 20%) later this year, and would like to put on an 11-28t cassette for those rides.

Is there a way to size the chain so that it can accommodate both cassettes?

Thanks!
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Old 03-17-14, 08:13 AM
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Derailer Adjustment

Big-big +1, based on the bigger cassette.
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Old 03-17-14, 08:55 AM
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If the chain is long enough for the 28T cog it will be fine for a smaller one. The 11T small cog is the same in either case. Another question is whether the rear derailleur will handle the larger 28T cog. Many will but since you have not specified anything other than "road bike" it is kind of hard to know for sure. A "B" screw adjustment will probably be needed in any case.
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Old 03-17-14, 09:51 AM
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Sram Force 10spd rear derailleur. Specs say it will take a 28 tooth cog.

What I'm confused about is if I use big-big +1 on the 28 tooth cog, won't the chain be too loose for the 11-23t cluster?
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Old 03-17-14, 10:03 AM
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Originally Posted by flats View Post
Sram Force 10spd rear derailleur. Specs say it will take a 28 tooth cog.

What I'm confused about is if I use big-big +1 on the 28 tooth cog, won't the chain be too loose for the 11-23t cluster?
Someone correct me if I'm wrong, but too loose would be a potential issue only with the 34x11 or maybe 12 combination, small-small. It's better in principle to have everything exactly right and qualified mechanics won't say this but I think we can usually get away with a link off in either direction.
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Old 03-17-14, 10:09 AM
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Set up the new chain for the 11-28 and make sure your derailleur will handle it, most modern road derailleurs have a rating for 27 teeth and this is often conservative.
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Old 03-17-14, 11:49 AM
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Originally Posted by flats View Post
Sram Force 10spd rear derailleur. Specs say it will take a 28 tooth cog.

What I'm confused about is if I use big-big +1 on the 28 tooth cog, won't the chain be too loose for the 11-23t cluster?
You are good for the 28T cog. Doesn't the 11x28 cassette have a 23T cog? Does it work there? Then the 11x23 will work too. As noted your small-small (34x11) is the same for both cassettes so the same chain will work for both.

The only potential problem is if you use the chain on the 11x23 for many miles and then install a new 11x28, the worn chain may skip on the new cogs. You might want to use both cassettes about equally to mate them to the same chain
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Old 03-17-14, 12:11 PM
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Originally Posted by wphamilton View Post
Someone correct me if I'm wrong, but too loose would be a potential issue only with the 34x11 or maybe 12 combination, small-small. It's better in principle to have everything exactly right and qualified mechanics won't say this but I think we can usually get away with a link off in either direction.
Maybe I can clarify.

The minimum chain length is based on big/big + 1" (pr. of links). (Sram method)
the maximum chain length is based on what can loop small/small without slack (Campagnolo method)
The correct chain is anything between these (inclusive) See Shimano tech for a guideline based on RD cage angle.

If the RD has enough capacity the minimum will be less than the maximum and all is good. If the RD lacks capacity, ie. short cage with wide range combination, the user has to make a choice; either change the gearing, change the RD, or possibly cut the chain based on minimum length, and not use the small combinations that cause the chain to sag.

Hope this helps.
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Old 03-17-14, 12:26 PM
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wear in the chain is a factor too ..
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Old 03-17-14, 12:50 PM
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But it's more critical to be above the minimum right? I mean if you have to have the same chain for both cassettes, it's easier to deal with a little slack in the small-small than to be too small for the big-big.

In other words I'd be inclined to set the chain for the 28 tooth erring on the side of shorter if it's in-between, and just be conscious of cross-chaining the small combo when using the other cassette, and that probably works adequately. If he has a medium or long cage.
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Old 03-17-14, 01:03 PM
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Originally Posted by wphamilton View Post
But it's more critical to be above the minimum right? I mean if you have to have the same chain for both cassettes, it's easier to deal with a little slack in the small-small than to be too small for the big-big.

In other words I'd be inclined to set the chain for the 28 tooth erring on the side of shorter if it's in-between, and just be conscious of cross-chaining the small combo when using the other cassette, and that probably works adequately. If he has a medium or long cage.
Yes, I lost the reference to the minimum being absolute when I edited the post. The final paragraph was basically what you said here. OK to fudge long, zero fudge room to the short side.

I know too many people who fudged short figuring they'd never shift to the big/big combination. Well never is a long time and stuff happens. Shifting to a combination the chain cannot loop, will bend the axle, break off the derailleur, fold the chainrings, or crack the dropout or chainstay. Any or any combination of these can and will happen, so you never fudge short no matter how good you think you are.
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Old 03-17-14, 02:29 PM
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Footnote to the minimum chain length question.

Many older derailleurs (pre-slant pantograph) such as Campagnolo, Huret and Simplex, have idler pulleys which cannot rise high enough to clear the straight line from the bottom of the largest sprocket to the bottom of the chainring (single speed chain path) and therefore the Sram big/big +1 method will produce a chain too short. Measuring this way and shifting to low will rip the derailleur apart.

So before measuring, bring the lower pulley up as high as possible and see where the stop is. Or measure the chain through the derailleur based on not hitting the stop limit when in big/big.
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Old 03-17-14, 02:31 PM
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if the chain is optimum length for 11x23 it may be too short for an 11x28.

if the chain is optimum length for 11x28 it may be too loose for an 11x23.

i can't define "too loose" or "too short" for the OP though.
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Old 03-17-14, 03:00 PM
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Originally Posted by hueyhoolihan View Post
if the chain is optimum length for 11x23 it may be too short for an 11x28.

if the chain is optimum length for 11x28 it may be too loose for an 11x23.

i can't define "too loose" or "too short" for the OP though.
The first depends on which method was used to set the "optimum" length. The Campagnolo method would most likely leave the chain long enough.

OTOH, any chain that is the right length for an 11-28 cassette is also fine for an 11-23, since the second is fully included within the first. Think of it this way, what if you kept the 11-28 and simply didn't use the 28t sprocket?
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