Inconsistent chain length calculations
05-05-22, 08:02 AM
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Inconsistent chain length calculations
I updated my recently acquired size 54 2010 Roubaix Comp's rear drive train to be a little more climbing friendly. The original rear drive train consisted of a rd-5600 derailleur with a 12-27 cassette, 27 teeth being listed as the max for that derailleur. I switched to a rd-5701-gs derailleur along with a 11-32 cassette which is spec'd to work with the 50-34 front chainring set. I was planning on using the chain length equation L = 2 × C + F/4 + R/4 + 1, which when I applied it to the original setup gave 105 for the number of links This matched the chain on the bike before I swapped the rear cassette from a 27T to 32T on the largest cog. Applying the equation to the new setup I get 107 links. Instead of just cutting 9 links off of my new KMC X10 that came with 116 links (including the "missing link") to get it down to 107, I tried to use the Park Tool Largest to Largest method. When I did this I ended up only cutting 6 links out so I end up with 110 links which is 3 links longer than the equation. I finished adjusting the H/L limits and the indexing and shifting is perfect both on the stand and on the road. So my question is should I leave it as is or trust the 107 number and remove 3 links? I did see other sizing advice that says a chain is too long if when on the derailleur and on the largest chain ring and cog, you can "fold" a link over. I can definitely fold a link when in this state, but probably not more than 1 link. Any other advice?
05-05-22, 08:11 AM
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05-05-22, 08:13 AM
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I've never used an equation to put a chain on a bike. It's either too loose or too tight...just go by feel and add or remove links as necessary.
Sometimes people over complicate this stuff...
Sometimes people over complicate this stuff...
Last edited by prj71; 05-05-22 at 09:58 AM.
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05-05-22, 08:24 AM
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This is why I don't follow the "repair by numbers" methods as the sole way to determine stuff. You test fitted the chain on the stand, confirmed that the length was not too short (the "dangerous" length
) and then test rode on the road. Exactly what I was referring to in this recent thread Is My Chain The Right Length? - Bike Forums I will; say you did the right thing. Andy
) and then test rode on the road. Exactly what I was referring to in this recent thread Is My Chain The Right Length? - Bike Forums I will; say you did the right thing. Andy
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05-05-22, 08:59 AM
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Page 28 of this .pdf
https://si.shimano.com/api/publish/s...001-26-ENG.pdf
Note that when you have bigger than a 27 toot cog on the rear you do not run the chain through the DR while determining it's proper length.
Big thing is just that after putting the chain back through the DR cage, when in the big big combo that the DR cage not be stretched to the it's absolute limit for forward travel. And when in the small small combo that your chain not go slack and droop.
Other methods for sizing chains work too.
https://si.shimano.com/api/publish/s...001-26-ENG.pdf
Note that when you have bigger than a 27 toot cog on the rear you do not run the chain through the DR while determining it's proper length.
Big thing is just that after putting the chain back through the DR cage, when in the big big combo that the DR cage not be stretched to the it's absolute limit for forward travel. And when in the small small combo that your chain not go slack and droop.
Other methods for sizing chains work too.
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05-05-22, 09:39 AM
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Does the chain smack the chain stay when in the lowest cassette tooth & smallest front ring?
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05-05-22, 09:42 AM
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05-05-22, 11:38 AM
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As long as the chain is not too tight in the big/big combo and not too loose in the small/small combo, you're fine. Some gear combinations allow you a range of acceptable chain lengths, and if anything I'd rather have the longer of those options just in case I want to get an even larger cog in the future.
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05-05-22, 12:27 PM
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Looks OK to me. Is there still tension on the rear derailleur? How's it look in big-big?
05-05-22, 01:09 PM
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without putting hands on it & going by the picture, I'd shorten it a link.
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05-05-22, 01:35 PM
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Thanks all! I think I am going to stick with what I have for now. I just realized I would need to remove 2 links one inner and one outer to shorten it with the missing link (unless I am missing something), and I think that would be too tight. If I hear any chain slap, start noticing any more droop, or start dropping the chain, I will re-consider.
05-05-22, 01:38 PM
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yes there is still tension on the rear derailleur, big big looks good, tho I might be able to fold one link.
05-05-22, 01:40 PM
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what does it look like when the chain is on the Big & Big?
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05-05-22, 01:48 PM
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I wouldn't remove any links. But that's just me.
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05-05-22, 02:05 PM
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Yeah, unless it's not running smoothly in small/small (which you shouldn't be using anyway), leave it be.
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05-05-22, 02:16 PM
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fwiw I like small/small sizing works vintage and modern
no calculations
no calculations
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05-15-22, 12:22 AM
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Thanks all! I think I am going to stick with what I have for now. I just realized I would need to remove 2 links one inner and one outer to shorten it with the missing link (unless I am missing something), and I think that would be too tight. If I hear any chain slap, start noticing any more droop, or start dropping the chain, I will re-consider.
05-15-22, 01:10 AM
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Her already did, look at post 17 of this thread
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05-15-22, 08:03 PM
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You want 1-2" of slack.
You want 1-2" of slack.
