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Chainring differential question

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  • 20-02-2020 2:18pm
    #1
    MojoMaker
    Registered Users Posts: 4,686 ✭✭✭


    Hi all,

    I want to run a 52/34 setup. I have the rings assembled to do it but an open question around whether e.g. a standard 6800 FD can work with this combo out of the box?

    Any potential issues elsewhere in the drive train? I'm not so sensitive to gaps or jumps, just mechanical performance.


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    #2
    Mefistofelino
    Registered Users Posts: 1,852 ✭✭✭Mefistofelino


    MojoMaker wrote: »
    Hi all,

    I want to run a 52/34 setup. I have the rings assembled to do it but an open question around whether e.g. a standard 6800 FD can work with this combo out of the box?

    Any potential issues elsewhere in the drive train? I'm not so sensitive to gaps or jumps, just mechanical performance.

    Shimano quote a capacity of 16T for the FD6800, whereas you'll need 18T (52-34). However I've always found that Shimano are quite conservative in the specifications, so it would be worth a try.

    Just bear in mind that there may be an issue with the rear derailleur. The RD6800 standard short cage has a 33T capacity. If you've used 18T for the front, then (in theory anyway) you're only left with 15T available for the range on the rear cassette (eg 11-26). Again, you could push this a bit but if you are planning to run a 11-28 or 11-30 at the back, you might find yourself in a bit of trouble overall with the chain too slack or too tight.


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    #3
    Everything Italian
    Registered Users Posts: 25 ✭Everything Italian


    Mefistofelino wrote: »
    Shimano quote a capacity of 16T for the FD6800, whereas you'll need 18T (52-34). However I've always found that Shimano are quite conservative in the specifications, so it would be worth a try.

    Just bear in mind that there may be an issue with the rear derailleur. The RD6800 standard short cage has a 33T capacity. If you've used 18T for the front, then (in theory anyway) you're only left with 15T available for the range on the rear cassette (eg 11-26). Again, you could push this a bit but if you are planning to run a 11-28 or 11-30 at the back, you might find yourself in a bit of trouble overall with the chain too slack or too tight.

    Related to this, and depending on the cassette you want to use, chain slack could be an issue as it has to be loose enough to manage the 52T with say 23T on the cassette (assuming here that you dont max out the cross-chaining thing..) but still tight enough not to slop about where you are in the 34-12/11. A clutch based RD is supposed to assist here, but I dont know much about them.

    All in all, I'd suggest it may be OK, if sub-optimal...


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