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  1. #1
    mtbr member
    Join Date
    Sep 2011

    IS to Post Mount adaptor help?

    Dear forum members,

    About a week ago someone gave me 2 wheels, including a 160mm Shimano rotor and Shimano Deore BR-M515 brake. I still have crappy v-brakes on my MTB so this would be a good step forward I think.

    Anyway, I found out I need a new fork. On the internet I saw a RockShox Dart 2 suspension fork, which looks good enough for my needs. But after some research I found out that my M515 brake still has the old 51mm IS (International Standard) mount instead of the newer 74mm Post Mount, and most suspension forks (including the Dart 2) got the Post Mount.
    So I started searching for a adaptor for IS to Post Mount, which I found a lot, like this one: Click!

    But now the problem: how should this thing be mounted? It can't be mounted on the sides of the brake pads, but on the other side of the brake pads it can't be mounted too as there's a bump for a screw comming through there. Too clear it up I took some pictures:

    Orginally the brake should be mounted like this on a IS mount:

    Oh, btw, the brake has already some sort of adaptor on it. At least it looks like one...

    It's hard to explain but I hope someone could help me with my problem.

    Thank you,


  2. #2
    B A N N E D
    Join Date
    Apr 2007
    You have a Post Mount brake that has a IS adapter on it, remove the black IS adapter and the brake caliper will bolt straight onto a PM fork when using a 160mm rotor.

    BR-M515 without the adapter.

  3. #3
    mtbr member
    Join Date
    Sep 2011
    Are you sure about that Cobba? Without the adapter the mount dimension is about 55mm, whereas I read on different sites that the dimension of a post mount is 74mm. Is this correct?

  4. #4
    B A N N E D
    Join Date
    Apr 2007
    Looks like I was wrong about it being a Post Mount caliper.
    You're right about Post Mount being 74mm.

    Shimano for some strange reason decided to make two different models of this brake, the BR-M515-LA and the BR-M515-LA-M

    The BR-M515-LA must be what you have, it looks like a Post Mount caliper but it's bolt holes are spaced at 55mm instead of the 74mm of a Post Mount, this brake and it's strange IS adapter can only be fitted to a IS mount fork.

    The BR-M515-LA-M is an actual 74mm Post Mount caliper that will bolt straight onto a Post Mount fork, this brake can be also fitted to a IS fork with the following adapter.
    Shimano Adaptor SM-MA-F160P-S Front PM to IS 160mm

    There is adapters for fitting IS calipers to Post Mounts but some will require up sizing the 160mm rotor by 20mm to a 180mm rotor.
    Hope Mount Adaptor Front IS to PM + 20mm (180mm rotor)
    Shimano Adapter SM-MA-F180S/P Front IS to PM 180mm (+ 20mm)
    A2Z Adapter IS To PM + 20mm (180mm rotor)
    KCNC Adapter IS to PM 160mm
    KCNC Adapter IS to PM 180mm (+ 20mm)

    * Looking at the shape of your current adapter and the clearances which would also be needed to fit your brake on one of the above IS to PM adapters, I'd say that it probably wouldn't work.
    * These adapters don't work with all IS mount brakes, clearance can be a issue.
    * I've seen photos where the 160mm adapter didn't have enough clearance to fit on a Post Mount fork. A fork with large diameter lowers will have shorter Post Mounts then a fork with smaller diameter lowers and the position of the fork ends / dropouts in relation to the lowers can also affect the length of the Post Mounts.

    I think that you basically only have 2 options:

    1) If you get a new Post Mount fork you will also have to get a new Post Mount brake to fit it.
    2) If you want to keep your current IS mount brake you will need to get a IS mount fork.

    Last edited by cobba; 09-29-2011 at 11:34 PM.

  5. #5
    mtbr member
    Join Date
    Sep 2011
    Cobba, thanks a lot for your answer. This definitely helps me. I will buy a post mount fork with a new post mount brake.

    Thanks A LOT!

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