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Thread: Post Mount

  1. #1
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    Folks interested in steel/ti post-mount hardware?

    So as a bit of background, I really like post-mount brake mounting setups. They work great, they're simpler and lighter than ISO, etc, etc.

    For several years I've been bugging Mark at Paragon to make (at the very least) a nice relieved post-mount fork tab in steel. I'd also like to see a version of his sliding dropouts with a PM tab on the disc side, or even (gasp!) a version of the low-mount disc dropout with one.

    He has been very resistant to the idea, partly because he's a very busy guy, and partly (I think) because he doesn't think the demand exists for the part.

    And yes, I am aware that I could spend a bunch of effort drawing something up and sending it out for bid to machine shops and so on. I still might end up doing that. But Mark is a much better part designer and machinist than me, and I don't really want the hassle - so I'm hoping to convince him to do it.

    So if you're interested in having something like this available, please post a response and say something about what material(s) you'd like to see and how many you might use in a year. I'm hoping that Mark is wrong and that there are actually a lot of us that want this.

    -Walt

  2. #2
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    we'd use steel ones, don't know how many though

  3. #3
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    It's not like I'm going to buy 50 of them, but yeah, if they were readily available I would buy a post-mount ready dropout instead of the current standard.

  4. #4
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    Post Mount

    I need education on the technical, not just perceived advantages to post mount, Walt has a thread up about having some parts made and I'm all for it, but why exactly. Lighter and simpler have been tossed around( today) but its the etc.etc. I am interested in. From a strength POV the PM eliminates a single shear attach for brakes but I have never seen a broken ISO attachment bolt. Lets hear some of you smart cats convince me. I'm not into gross overstatement but by I do think that the ISO mount is an easier fab at this point, and based on the lack of interest by one of the main parts suppliers there must be something going on here.

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    Great thread, can't wait to hear.....expiring minds want to know.

    -Schmitty-

  6. #6
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    I have little experience with pm. Are you locked into a given rotor size when using pm? Maybe on larger rotos sizes the posts get fragile? Why bother?

    -Schmitty-

  7. #7
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    My perceptions

    Here are my thoughts (as someone who likes post mount stuff and has built with it in the past):

    Good:
    -Fewer bolts and less mounting/adapting hardware = simpler and lighter attachment of caliper to fork/frame/dropout.
    -No shear forces on mounting bolts, though as Wade points out, it's not like they ever break with ISO.
    -Changing rotor sizes requires a relatively simple/cheap adapter (see http://www.probikekit.com/iframe.php?code=NP09461 for a picture of a 160/180 adapter) that isn't any more complicated than an ISO adapter for different rotor sizes.

    Neutral/bad:
    -Suspension forks are almost universally post-mount now, which means more and more customers are asking me fork post-mount rigid forks to match. I would assume ISO disc calipers will eventually go the way of the Dodo, at least for the front. Could be a while before that happens, though.
    -Some caliper designs don't allow much adjustability, no facing/alignment tools exist to my knowledge. So the mount needs to be pretty accurately attached - you can't face it and fix problems after the fact.
    -Probably a pain with some traditional steel fork configurations, due to the location of the dropout/fork blade vs disc mount. Then again, this is already the case for ISO sometimes.

    -Walt

  8. #8
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    Along the lines of what Walt said, when someone is using a hub that doesn't have the rotor in the correct location (e.g., Chris King hubs), you may severly run out of room within the caliper's range of adjustment.
    May the air be filled with tires!

  9. #9

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    Hi Walt,

    there is a facing tool available - look here
    I havent used it until now. It is designed for facing fork-postmounts - I dont know if it is useful for rear-pm.

    Ulrich

  10. #10
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    I just don't see the point of welding something that is obsolete to a bike frame really. That's the biggest problem I've got with ISO. PM is all that's left in new forks, new brakes, etc., so why prolong ISO?

    PM looks cleaner, is cleaner, requires half the hardware, is lighter, is the "current standard".

    I'd like to see a GA PM that could be welded to a frame/fork. I'd use 1/yr currently and for the next few years probably.

    So that's my opinion, and we all know what that's worth.

  11. #11
    pvd
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    There are post/post adapters for larger rotors.

    Shimano F180P/P & F203P/P will adapt a 160mm PM to other rotor sizes, but you can get cleaner looks if you place things more specifically.

    I'd love some nice parts and tools for doing PM front and rear.

    One important issue is facing the surface square. Tricky tooling.

  12. #12
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    Quote Originally Posted by vulture
    I need education on the technical, not just perceived advantages to post mount, Walt has a thread up about having some parts made and I'm all for it, but why exactly. Lighter and simpler have been tossed around( today) but its the etc.etc. I am interested in. From a strength POV the PM eliminates a single shear attach for brakes but I have never seen a broken ISO attachment bolt. Lets hear some of you smart cats convince me. I'm not into gross overstatement but by I do think that the ISO mount is an easier fab at this point, and based on the lack of interest by one of the main parts suppliers there must be something going on here.
    One of the nice things about PM is the same bracket is used F&R for larger rotors.

    Can not use a 140mm rotor with PM.

    Functionally I find little difference between PM and IS. I have built a few forks and a frame with PM and it was fairly easy. Used canti bosses for the forks.
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  13. #13
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    Is there such a thing as pm integrated dropouts?

    -Schmitty-

  14. #14
    pvd
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    Quote Originally Posted by shiggy
    Can not use a 140mm rotor with PM.
    How's that? Sure, standard parts are not available for front as for rear, but I had no problem putting a 140mm rotor on a fork I made using PM caliper on an IS adapter. If this can be done, it should be easy with a direct PM mount.

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    I think it would be easy to make a tool to face these. All it takes is a dummy axle and a flat piece of angle iron welded on in the proper orientation to use as a file guide. You shouldn't need to shave more than .005" if you put it on straight, and a sharp file will take care of that easily.

    Yea, it's not a fancy solution, but how much time would really be saved with something fancier? You could always add a hardened face plate to the angle iron as well.
    Too many bikes, not enough time.

  16. #16
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    There are at least two I know of...

    Quote Originally Posted by Schmitty
    Is there such a thing as pm integrated dropouts?

    -Schmitty-
    DWL Turner Sultan and Salsa Mamasita....probably many more.
    "I can only assume chan slap is what happens when you get assaulted by Jackie Chan. I don't think anybody can prevent that."

  17. #17
    meh....
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    as a user, PM is easier to set up. No shims needed for side to side, and you can fine tune the effective caliper contact diameter with washers/shims, as long as you need to make it bigger. Though I suppose you could remove a bit of material if the PM was "too big".

  18. #18
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    Isn't there another thread about this from mid this year?

    Anyway, I'm running constant diameter 22.2 stays on our Arete and Arete Ti, and I'd love some post mounts like these [attached]....

    But yeah Walt, I'd love to see post mounts across the board, but I can see why Mark doesn't want to do them. It's an extra set-up and a complicated one at that.

    But hey, money talks and all that.
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  19. #19
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    Quote Originally Posted by pvd
    How's that? Sure, standard parts are not available for front as for rear, but I had no problem putting a 140mm rotor on a fork I made using PM caliper on an IS adapter. If this can be done, it should be easy with a direct PM mount.
    Sure, you can make one, but it will be a non-standard PM.

    I have a bike with a front 140mm rotor, too. Rigid fork with rear IS tabs. The caliper is "post mount" with an IS bracket but once the bracket goes on I consider it an IS caliper.

    If you use the published PM spec, the mounting face to axle distance is the same front and rear, unlike the IS spec. Smallest possible rotor size with this spec is 160mm.
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  20. #20
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    Quote Originally Posted by Schmitty
    Is there such a thing as pm integrated dropouts?

    -Schmitty-
    None for use by framebuilders AFAIK.

    The Salsa Fargo has sweet cast/forged? PM front and rear, and chainstay mounted. I asked about availability for framebuilders, since some of their other dropouts are sold individually. No-Go.
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  21. #21
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    Quote Originally Posted by Thylacine
    Isn't there another thread about this from mid this year?

    Anyway, I'm running constant diameter 22.2 stays on our Arete and Arete Ti, and I'd love some post mounts like these [attached]....

    But yeah Walt, I'd love to see post mounts across the board, but I can see why Mark doesn't want to do them. It's an extra set-up and a complicated one at that.

    But hey, money talks and all that.
    I like it!
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  22. #22
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    My Aunt owns a machine shop, if anybody has drawings with dimensions I can get them machined up, of course the more that are ordered the cheaper they will get.
    Quote Originally Posted by thefuzzbl
    aluminium has a tendency to fail when you need it most. i.e. you end up with a bad day.

  23. #23
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    Quote Originally Posted by Thylacine
    Isn't there another thread about this from mid this year?

    Anyway, I'm running constant diameter 22.2 stays on our Arete and Arete Ti, and I'd love some post mounts like these [attached]....

    But yeah Walt, I'd love to see post mounts across the board, but I can see why Mark doesn't want to do them. It's an extra set-up and a complicated one at that.

    But hey, money talks and all that.
    Warwick,
    Got a link to post mount geometry? I've got dropouts in the works...

    I could take a look at your weld on bit too.

  24. #24
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    From the Hayes site:

    For those who are curious:
    http://www.hayesdiscbrake.com/support_downloads.shtml

    Scroll most of the way down the page to "Industry Standard Mounts" and download it.

    I'll see if I can post it, but it's a .pdf... not sure if that will work.

    _Walt

    Quote Originally Posted by Kavik
    Warwick,
    Got a link to post mount geometry? I've got dropouts in the works...

    I could take a look at your weld on bit too.
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  25. #25
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    Quote Originally Posted by Kavik
    Warwick,
    Got a link to post mount geometry? I've got dropouts in the works...

    I could take a look at your weld on bit too.
    I've blown all my spare cash for this year Brian so the post mounts will have to wait.....unless you want to make them yourself Just don't show them to Felt, m'kay.
    No longer member of the bike industry nor society, so don't hassle me.

  26. #26
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    Walt,
    I asked you about a PM rear option a while ago. I undersatnd why ISO prevails, easier to make, no tapped holes, easier to fix/locate, easier to face.

    As a user though I am done with ISO. I agree with the obsolete comment. Every disc brake in my household is PM so an adapter feels like a halfa ss way at doing things. ISO brakes and Shims are a major pain especially if you take your wheels off all the time. I want my next bike to be all PM front and rear.

    Keep hammering PMW.

  27. #27
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    Food for thought...
    "IS" mounts are just holes, and the caliper mounting bolts thread into the adaptor.
    If you strip one out, you can replace a cheap part.

    "PM" tabs are threaded, so if they strip the fork or frame is damaged.
    Heliocoil thingys are a halfassed fix.

    The new DW Turners have post mounts with replacable inserts.
    This sounds like the best of both worlds.
    On a nice handmade frame, i would want to see the most longevity possible.

  28. #28
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    It would be pretty freaking hard....

    ... to strip M6 threaded steel. I don't think that's really a concern. I mean, you don't worry about stripping a canti/v-brake boss much, right? Heck, how many times has anyone managed to strip an aluminum Avid ISO adapter? I've *never* heard of it happening. M6 is a pretty big bolt.

    I'm sure someone could do it, but I don't think it's something you would ever see on a steel bike. Just IMO, of course.

    -Walt

    Quote Originally Posted by erosive
    Food for thought...
    "IS" mounts are just holes, and the caliper mounting bolts thread into the adaptor.
    If you strip one out, you can replace a cheap part.

    "PM" tabs are threaded, so if they strip the fork or frame is damaged.
    Heliocoil thingys are a halfassed fix.

    The new DW Turners have post mounts with replacable inserts.
    This sounds like the best of both worlds.
    On a nice handmade frame, i would want to see the most longevity possible.

  29. #29
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    Quote Originally Posted by Walt

    I'm sure someone could do it, but I don't think it's something you would ever see on a steel bike. Just IMO, of course.
    t
    Yeah, I was wondering about this. I'd never strip one in a custom frame. I'd be thinking about how long I waited, the scrilla dropped, etc. and would do it right and think about it when putting a brake on. In other words, I'd think the customer that was interested in a custom frame would have enough sense not to overly crank down a bolt. Now the regular idiot could probably do it. Good point though, erosive, it is a check for "negative". I'd still rather not have an obsolete boss welded on my bike if I didn't have to because it is so ugly. I'd take the chance.

  30. #30
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    What is the best way to correct alignment on a post mount on a frame? Facing the post mount doesn't change the angle of the threaded hole, so if you did face it then the bolt head wouldn't tighten flush against the top of the caliper, right? Is that too theoretical and it actually doesn't have much effect in practice? In my mind the truly ideal way would be to bend the whole mount back into alignment

  31. #31
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    Quote Originally Posted by erosive
    Heliocoil thingys are a halfassed fix.
    Helicoils are a great fix and can sometimes be stronger than the threads that they replaced. Some applications even use helicoils on purpose for thread engagement (not as a fix), instead of the base material. Porsche commonly did this on magnesium engine and transmission parts, and some WWII airplanes also used them for fasteners that were regularly removed and retorqued for maintenance.
    Too many bikes, not enough time.

  32. #32
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    Quote Originally Posted by boomn
    What is the best way to correct alignment on a post mount on a frame? Facing the post mount doesn't change the angle of the threaded hole, so if you did face it then the bolt head wouldn't tighten flush against the top of the caliper, right? Is that too theoretical and it actually doesn't have much effect in practice? In my mind the truly ideal way would be to bend the whole mount back into alignment

    Maybe run a set of the Avid cocave/convex washers and take their additional stack height into account when setting the post length?


    -Schmitty-

  33. #33
    pvd
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    Quote Originally Posted by shiggy
    Sure, you can make one, but it will be a non-standard PM.
    ...
    If you use the published PM spec, the mounting face to axle distance is the same front and rear, unlike the IS spec. Smallest possible rotor size with this spec is 160mm.

    That's exactly what I do. I make things. I know the rules and I know how to break them. 140mm PM is no problem.

    I have the Shimano Spec at home. I keep forgeting to scan it in. I'll try to remember.

  34. #34
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    Quote Originally Posted by boomn
    What is the best way to correct alignment on a post mount on a frame? Facing the post mount doesn't change the angle of the threaded hole, so if you did face it then the bolt head wouldn't tighten flush against the top of the caliper, right? Is that too theoretical and it actually doesn't have much effect in practice? In my mind the truly ideal way would be to bend the whole mount back into alignment
    if the PM was off and facing the posts made them 'correct' but the bolt holes were still off, tightening the caliper down would make it reference to the faces on the posts, not the off kilter bolt heads. if the bolt holes were far enough off you might have a problem, but most likely you could add a couple washers and they would take the bearing pressure of the bolt head and spread it out into the caliper.

  35. #35
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    Quote Originally Posted by Schmitty
    Maybe run a set of the Avid cocave/convex washers and take their additional stack height into account when setting the post length?


    -Schmitty-
    Or just run Avid brakes. The CPS washers are already accounted for.

    I used an old BB7 as my "jig" for post mounts.
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  36. #36
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    Quote Originally Posted by Walt
    For those who are curious:
    http://www.hayesdiscbrake.com/support_downloads.shtml

    Scroll most of the way down the page to "Industry Standard Mounts" and download it.

    I'll see if I can post it, but it's a .pdf... not sure if that will work.

    _Walt
    That is for front 100mm QR, of course. The only difference for rear or front 110mm 20mm TA is the lateral spacing, which can be adjusted using the numbers from the IS specs.
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  37. #37
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    Don't forget the bolts are not in sheer like they are with ISO.

    Seriously, alignment and thread 'issues' are non-issues in steel.

    The only hurdle is the extra setup required to machine the damn things on three different sides, so you could expect the cost of a part with post mount to be at least a third more expensive.
    Last edited by Thylacine; 10-30-2009 at 04:46 PM.
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  38. #38
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    Quote Originally Posted by Thylacine
    Don't forget the bolts are not in sheer like they are with ISO.

    Seriously, alignment and thread 'issues' are non-issues in steel.
    Seems like bolt sheer is a non issue in a bike app.

    -Schmitty-

  39. #39
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    Depends on how tightly you screw them in
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  40. #40
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    Quote Originally Posted by Walt
    ... to strip M6 threaded steel. I don't think that's really a concern. I mean, you don't worry about stripping a canti/v-brake boss much, right? Heck, how many times has anyone managed to strip an aluminum Avid ISO adapter? I've *never* heard of it happening. M6 is a pretty big bolt.

    I'm sure someone could do it, but I don't think it's something you would ever see on a steel bike. Just IMO, of course.

    -Walt
    I have heard of people stripping the PM threads in forks, usually because they used a too-short bolt.
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  41. #41
    pvd
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    Hey guys. Here's the Shimano spec for PM that I promised. I belive that it is much nicer than the Hayes spec.



    https://www.pvdwiki.com/index.php?ti...mebuilder_Info

  42. #42
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    The only issue that I really have with post mounts is this - as a mechanic, working on a fork for rebuild/fluid replacement/etc... you have to remove the caliper from the fork in most cases. This is a very simple thing to do with the I.S. mount - you unscrew 2 bolts, remove the caliper, let it hang below the lever somewhere when you store the H/bar and then when you are done with the fork, you put it back on with the same 2 screws - no alignment or resetting is required 90+% of the time, and if you keep the caliper below the lever there should be no issues with some "hidden" bubble in the brake system finding it's way into the line. (though of course, if there is that bubble the brakes will need work anyway...). For most jobs involving the brake caliper, I.S. mounts make it much easier to remove/affix the caliper without having to reset the caliper in relation to the disc. Post mounts are clean and light, but I am not sure I think that they are better... Just my .02
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  43. #43
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    The biggest problem I have with Post Mount is that it lacks significant lateral adjustability without end user mods. Makes you more reliant on hub, rotor, and caliper mfr's all playing nice with each other. This is currently a problem with some part combinations. Also note that in the four different specs I have for Post Mount, they all vary in their callout dimensions as there is no ISO standard. Not by huge margins, but it greatly increases the tolerance stack. But hey, it's the bike industry....
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  44. #44
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    Hey, the bike industry has standards. They're just very.....low.
    No longer member of the bike industry nor society, so don't hassle me.

  45. #45
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    Hi Walt,
    I would also be interested by a version of the Paragon low-mount disc dropout with PM.
    In fact I've drawn my own version that I plan to have laser or water-jet cut soon (they will require brazing too little turned parts for the attachment itself).
    BTW, did you try asking Kirk Pacenti ?

  46. #46
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    Quote Originally Posted by DWF
    The biggest problem I have with Post Mount is that it lacks significant lateral adjustability without end user mods.
    Please don’t interpret this as being belligerent but am I missing something here? How would a PM caliper on a PM frame have any less adjustability than a PM caliper on an IS adapter on an IS frame?
    Regarding PM caliper to IS frame: How would adding an adapter with its own tolerance stack plus the added effect of hole location and flatness of the IS side and perpendicularity or the PM threads be less tolerance stack than straight PM to PM?

    It seems so much better to run a set up with out an adapter.
    IS to IS is simple but requires shims and makes any trail side adjustment a bit of a pain. PM to PM is better assuming everything is square. If you need to adjust all you need is a 5mm hex instead a bag of shims and some time for experimenting.

  47. #47
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    Quote Originally Posted by gte819s
    Please donít interpret this as being belligerent but am I missing something here? How would a PM caliper on a PM frame have any less adjustability than a PM caliper on an IS adapter on an IS frame?
    Regarding PM caliper to IS frame: How would adding an adapter with its own tolerance stack plus the added effect of hole location and flatness of the IS side and perpendicularity or the PM threads be less tolerance stack than straight PM to PM?

    It seems so much better to run a set up with out an adapter.
    IS to IS is simple but requires shims and makes any trail side adjustment a bit of a pain. PM to PM is better assuming everything is square. If you need to adjust all you need is a 5mm hex instead a bag of shims and some time for experimenting.
    with PM to IS you can shave down the IS mount and the adapter to move further outboard. With PM on PM you can only go so far before you have to start filing out the caliper itself

  48. #48
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    Ah Right

    More material can be removed from the IS tab than can be removed from the PM caliper to move the caliper outward.

    But modifications are still done to make it work outside of the 'standard'.

    I have not put enough bikes together to run into this issue but i can guess it happens more on zero dish SS wheels with a wide flange or shallow spoke angles on 29ers.

  49. #49
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    Quote Originally Posted by gte819s
    Ah Right

    More material can be removed from the IS tab than can be removed from the PM caliper to move the caliper outward.

    But modifications are still done to make it work outside of the 'standard'.

    I have not put enough bikes together to run into this issue but i can guess it happens more on zero dish SS wheels with a wide flange or shallow spoke angles on 29ers.
    most problems i've heard have been with fork and hub combos. For example the new PM thru axle Reba's seem to have more problems than other forks, especially with hubs like King which are on the outer end of the IS spec for their rotor mount

  50. #50
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    Quote Originally Posted by gte819s
    Ah Right

    More material can be removed from the IS tab than can be removed from the PM caliper to move the caliper outward.

    But modifications are still done to make it work outside of the 'standard'.

    I have not put enough bikes together to run into this issue but i can guess it happens more on zero dish SS wheels with a wide flange or shallow spoke angles on 29ers.
    Yep, PM has very little lateral adjustment either towards the rotor or away from it before you have to start hogging out the caliper holes. With IS, this isn't a problem, you can shim towards the rotor or you remove material from the adapter to move it away from the rotor. Neither affects the integrity of your caliper.
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  51. #51
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    Quote Originally Posted by DWF
    Yep, PM has very little lateral adjustment either towards the rotor or away from it before you have to start hogging out the caliper holes. With IS, this isn't a problem, you can shim towards the rotor or you remove material from the adapter to move it away from the rotor. Neither affects the integrity of your caliper.
    Most post mount calipers are already slotted for more lateral adjustment than need in most cases. The adjustment is much easier to make than when dealing with shims or milling.
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  52. #52
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    Quote Originally Posted by shiggy
    Most post mount calipers are already slotted for more lateral adjustment than need in most cases. The adjustment is much easier to make than when dealing with shims or milling.
    Most < all. ISO gives you the option.
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  53. #53
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    Personally, I loathe post mount.
    I was a mechanic in the early days of disc brakes when all Manitou forks came with post mount and everything else was ISO. I got tired of fixing stripped threads.

    I will never buy a frame or fork with post mount. Last year, I bought a new Rock Shox Lyric and bought a year old one (NOS) just so I could get the ISO mount.

    I may sound like a grumpy old man on this, but the weight savings are minimal and the downsides are significant.

  54. #54
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    Quote Originally Posted by DWF
    or you remove material from the adapter to move it away from the rotor. Neither affects the integrity of your caliper.
    Maybe not on the caliper but you are reducing the shear area and the thread engagement on the joint/adapter. Possibly this is negligible and really just being nit picky.
    If the situation were to exist where the hub was so far out what would you do with an IS to IS? Face off the tabs to get the exact lateral outward movement? If it was decided not to touch the frame/fork then what tooling exists to shave the caliper or adapter flat other than using a mill?

    The IS to IS leaves you with zero lateral adjustment other than shimming or removing material. The PM at least covers you for most lateral adjustments in both directions. Its not perfect for all combinations but possibly that can be improved by widening the tab and slot as a refined design.

    From this thread it is clear that it does come down to personal experience and preference. IS to IS, PM to adapter to IS, PM to PM. However frame options for PM is tiny and frame builders donít seem to be moving in the same direction as fork manufacturers.
    Im just hoping that demand will force PM sliders and PM dropouts.

  55. #55
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    The post mount on the new tunners are pretty sweet a removable steel stud with threading ...

    kinna handy "if" you do manage to strip it....

    I haven't run into to many issues with post mounts but i can see where you might run into em...
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  56. #56
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    Any updates with the steel post mount tab for adding to unicrown and segmented steel forks? Thylacine has the most promising and pleasing blueprints! Civia released a steel unicrown with a ISO tab Paragon-like PM mount, but it's lacking in a couple areas: 1) only one cable guide is needed 2) the PM mount could be cleaner.
    Creator Producer: Will of the Sun WoS, Author Platform Pedal Shootout 1M+ MTBR thread

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