Chain Length calculation?
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Chain Length calculation?
Thought it would be interesting in using the chain length calculation and compare to sizing the chain using Largest cog and largest chainring method.
The calculation is:L = 2 (C) + (F/4 + R/4 + 1)
The calculation is:L = 2 (C) + (F/4 + R/4 + 1)
- L = Chain length in inches
- C = Chain stay length in inches
- F= Number of teeth on biggest front chainring
- R= Number of teeth on biggest back cog.
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Yes, a master link is included in the chain length. Without a master link the chain would be joined by reusing a standard pin (older 5/6-speed) or a special joining pin (7+ speed). The "+1" accounts for the extra chain length required to allow the chain to clear the cog or chainring teeth height while shifting.
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I never calculate.... what works well for me for both modern and vintage (friction) setups is small/small sizing
and of course Big/Big combo has to work
and of course Big/Big combo has to work
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Yup. No need for a calculator, and the numbers put into the calculation are subject to operator error in measurement. Small/small gives the right length and if you are cheating by needing more chain wrap than the derailleur can handle then you need to double check with a big/big confirmation and expect the chain to hang slack in the small/small.
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Calculating chain length is about the most stupid way to figure it out. Put the chain on the bike and use the recommended method for the particular drivetrain you have.
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No need to overthink this-
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Yes, a master link is included in the chain length. Without a master link the chain would be joined by reusing a standard pin (older 5/6-speed) or a special joining pin (7+ speed). The "+1" accounts for the extra chain length required to allow the chain to clear the cog or chainring teeth height while shifting.
thankx for the heads up on this.
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The master link is 0.5 in the +1 of the calculation. All the above approaches work but testing big-big in the stand is critical.
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I almost think such posts which use math instead of simply measuring stuff are intended to be ironic?
Last edited by Camilo; 06-29-22 at 02:18 PM.
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aaah ok then my chain is a bit long. I wasn't sure if the master link was part of the calculation so i didn't cut the chain and added the master link. So, I will attached one side of the master link, and re-measure the chain from end to end.
thankx for the heads up on this.
thankx for the heads up on this.
Yeah, this sounds critical, but maybe there's a good reason to use a calculation that I don't understand? Can you explain if so.
Last edited by Camilo; 06-29-22 at 02:20 PM.
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Exactly @Camilo, this is why not any drivetrain manufacturer uses a formula of any kind.
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Formulas tend to be very exact and don't take into account every possible component group, cassette range or chain ring difference.
In reality there isn't an exact number of links your chain must be and one more or less might do better or might perform the same for a particular bike.
The big thing in sizing a chain is just knowing what to look for. If your chain sags when in the small/small then it might be too long. If the rear DR cage is stretched to it's forward limit when in the big/big then your chain might be too short.
In reality there isn't an exact number of links your chain must be and one more or less might do better or might perform the same for a particular bike.
The big thing in sizing a chain is just knowing what to look for. If your chain sags when in the small/small then it might be too long. If the rear DR cage is stretched to it's forward limit when in the big/big then your chain might be too short.
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Formulas tend to be very exact and don't take into account every possible component group, cassette range or chain ring difference.
In reality there isn't an exact number of links your chain must be and one more or less might do better or might perform the same for a particular bike.
The big thing in sizing a chain is just knowing what to look for. If your chain sags when in the small/small then it might be too long. If the rear DR cage is stretched to it's forward limit when in the big/big then your chain might be too short.
In reality there isn't an exact number of links your chain must be and one more or less might do better or might perform the same for a particular bike.
The big thing in sizing a chain is just knowing what to look for. If your chain sags when in the small/small then it might be too long. If the rear DR cage is stretched to it's forward limit when in the big/big then your chain might be too short.
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Formulas tend to be very exact and don't take into account every possible component group, cassette range or chain ring difference.
In reality there isn't an exact number of links your chain must be and one more or less might do better or might perform the same for a particular bike.
The big thing in sizing a chain is just knowing what to look for. If your chain sags when in the small/small then it might be too long. If the rear DR cage is stretched to it's forward limit when in the big/big then your chain might be too short.
In reality there isn't an exact number of links your chain must be and one more or less might do better or might perform the same for a particular bike.
The big thing in sizing a chain is just knowing what to look for. If your chain sags when in the small/small then it might be too long. If the rear DR cage is stretched to it's forward limit when in the big/big then your chain might be too short.
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Here's how you determine chain length for my DA 7700 derailleur: With the chain on the smallest cog and the largest chainring, the two pulleys on the rear derailleur should be perfectly vertical--90 degrees perpendicular to the ground. Straight from the manual.
Works every time for me.
Works every time for me.
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So you actually size the chain based on the calculation rather than just sizing it the way it's supposed to according to every authoritative source? (derailleur manufacturers, professional shops, etc.) Wouldn't you actually test the chain length after cutting it according to the calculation, and if so, why would you not do it the easy/correct way first?
Yeah, this sounds critical, but maybe there's a good reason to use a calculation that I don't understand? Can you explain if so.
Yeah, this sounds critical, but maybe there's a good reason to use a calculation that I don't understand? Can you explain if so.
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About the only use for doing the calculation in advance rather than actually fitting the chain would be to see if the chain you want to buy will be long enough. New chains come in different lengths, 112, 114, 116, etc links. If your calculation says you need 114 links you would want to avoid buying a chain 112 links long.
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Totally depends on how far forward you pull the derailleur cage.That's why you should follow the drivetrain manufactures recommendations. On older road bikes and mtbs that are completely within capacity spec you can use small/small and you'll get the longest chain possible, which is a good thing. Big/big is totally dependent on the chain installers preference.
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Here's how you determine chain length for my DA 7700 derailleur: With the chain on the smallest cog and the largest chainring, the two pulleys on the rear derailleur should be perfectly vertical--90 degrees perpendicular to the ground. Straight from the manual.
Works every time for me.
Works every time for me.
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Feel free to argue with Shimano if you must:
RD-7700
God, for some reason you guys make sizing a chain the most complicated thing about bikes.
Last edited by smd4; 07-01-22 at 07:59 AM.
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