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  1. #1
    Senior Member bellweatherman's Avatar
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    Post-mount disc brakes: changing from 160mm to 140mm?

    Is it possible to change from 160mm to 140mm disc brakes and rotors if your frame has post-mount (not ISO) disc tabs? Do frames welded with post-mount tabs allow adjustability when changing to different rotor diameters?
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    Senior Member mechBgon's Avatar
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    Interesting question. As you probably noticed, post-mount rear disc setups aren't common. If your caliper jives with a 160 when not using an adapter, then it's safe to say 160 is your effective minimum size. If your caliper lines up to a 160 with an adapter, then a 140 may work with the adapter left out. Consult the frame manufacturer if it's unclear whether it'll work or not.

  3. #3
    Senior Member bellweatherman's Avatar
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    Quote Originally Posted by mechBgon View Post
    Interesting question. As you probably noticed, post-mount rear disc setups aren't common. If your caliper jives with a 160 when not using an adapter, then it's safe to say 160 is your effective minimum size. If your caliper lines up to a 160 with an adapter, then a 140 may work with the adapter left out. Consult the frame manufacturer if it's unclear whether it'll work or not.


    This is specifically why I posed the original question as there is no manufacturer that i am aware of that even offers a manual about the braze-ons and other fittings on a frame.

    Plus, AFAIK, there is no such thing as an adapter for changing to different diameter disc brakes and rotor size.
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  4. #4
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    I thought there were ISO to post mount adapters to change disc sizes?
    I've never seen a post to post mount adapter that allows different sizes, however.
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    you can upsize but not downsize unless an adapter is already on. most specialized mtb with post mount will fit a 140. my crux disc is 140 rear with no frame clearance for bigger rotors.

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    Senior Member bellweatherman's Avatar
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    The original poster (i.e., me) stated that the frame in question has post-mount disc tabs, not ISO. Sorry, that was not clear.

    Anybody ever seen a post-mount adapter? I don't believe they exist.
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  7. #7
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    +20 and +40 adapters are readily available http://www.artscyclery.com/descpage-AVAPA185.html

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    It's much easier to go larger than smaller, if the frame / forks have a post mount, you are most likely limited to 160mm smallest, 203mm largest via Post to Post adaptor.

    Post mount is becoming the standard mount, it already is for forks, and is slowly going that way for frames, all disc calipers are now post mount, and use adaptors to go IS.

    What is the need for going down to 140mm? this is almost a dead size, Shimano only ever did it in XTR, and Avid still persist with the BB series, but road disc when they come out will most likly be F180mm/R160 for modulation, killing 140mm forever.

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    Quote Originally Posted by jimc101 View Post
    It's much easier to go larger than smaller, if the frame / forks have a post mount, you are most likely limited to 160mm smallest, 203mm largest via Post to Post adaptor.

    Post mount is becoming the standard mount, it already is for forks, and is slowly going that way for frames, all disc calipers are now post mount, and use adaptors to go IS.

    What is the need for going down to 140mm? this is almost a dead size, Shimano only ever did it in XTR, and Avid still persist with the BB series, but road disc when they come out will most likly be F180mm/R160 for modulation, killing 140mm forever.
    i just got my crux with 140mm rotor on the rear the other day. already dislike it. not enough power combined with the long full length housing run. frame has no clearance for 160mm. the front 160mm is fine for road duty. i like my brakes powerful with low hand effort

  10. #10
    Senior Member mechBgon's Avatar
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    Quote Originally Posted by bellweatherman View Post
    Anybody ever seen a post-mount adapter? I don't believe they exist.
    Yeah, they're commonplace actually.

  11. #11
    Senior Member bellweatherman's Avatar
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    Quote Originally Posted by mechBgon View Post
    Yeah, they're commonplace actually.


    Link?
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    Try Googling! there are lots available, here are a couple for you to start with

    http://techdocs.shimano.com/media/te...9830667774.PDF

    http://www.chainreactioncycles.com/M...?ModelID=13729

  13. #13
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    Why smaller?? If I may ask. I've always liked my brakes as big as possible....

  14. #14
    Senior Member mechBgon's Avatar
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    Quote Originally Posted by bellweatherman View Post
    Link?
    Well, I could walk up and down my showroom and point some out on Trek Fuel EX's, they're stock equipment. Anywhere you can buy a disc adapter, there should be post-mount models for rotor size changes.

    Why smaller?? If I may ask. I've always liked my brakes as big as possible....
    Weight. Big rotors are heavy, and how much brake power do you actually need on a rear brake (barring tandems)?

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