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  1. #1
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    Which front fork brake mount is better - Post or IS?

    Hi everyone.

    I just wondered what your opinion is on brake mounting standards.
    Which front fork brake mount is better - Post or IS?

    My reason for asking is that I may buy a 2008 Fox Talas front fork with IS mounts.
    My brakes will fit with the correct IS or post adaptors, but it seems that all the new forks are post mount.

    What are your experiences with the different mounts, any pros / cons...?

    Thanks for your advice.

    tBike

  2. #2
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    You probably won't notice much difference. In theory is mounts are weaker because they introduce shear to the bolts.

    Post mount brakes are much more common and you can obviously get a post mount to is adaptor.

    You might run into trouble with an is brake onto a post mount fork.

  3. #3
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    Quote Originally Posted by photosheikh View Post
    Hi everyone.

    I just wondered what your opinion is on brake mounting standards.
    Which front fork brake mount is better - Post or IS?

    My reason for asking is that I may buy a 2008 Fox Talas front fork with IS mounts.
    My brakes will fit with the correct IS or post adaptors, but it seems that all the new forks are post mount.

    What are your experiences with the different mounts, any pros / cons...?

    Thanks for your advice.

    tBike
    Both designs are flawed because they are lateral mounts. But if you are using mechanical brakes you are better off using a "post fork" with a "post caliper" because there will be less outward pressure on the caliper and rotor. Mechanical brakes force pressure to weakest point of the caliper, the outside edge, (further away from caliper mount), whereas a good hydro caliper with two or more pistons will force pressure to the center of caliper, (closer to the caliper mount). But overall post is a much stronger mount and allows for a much truer, (less lateral) braking surface.

  4. #4
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    Thankyou khskenny and fataqui. Your comments have helped me.

    I was concerned about the torque forces in comparison between the two mounts.
    Thank goodness for adaptors!

  5. #5
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    If "IS" in so inferior, then why are cars and motorcycles still using that style mount? That's what I don't get.

  6. #6
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    Post mounts are easier to set up but IS mounts make brake pad swaps easier since you can just pull the mount and pull the pads out. At least this is the case with bottom loading brake pad designs. Top-loading calipers would be just as easy for both mounts.

  7. #7
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    IS (51mm)nicely fit to the fork or rear mount and it looks pretty clean, however it takes longer to setup properly. Check out these beauty Blue 29er.

    PM (74mm) are very practical, super easy to set up. Probably stronger for the bigger size rotors as well.

  8. #8
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    Quote Originally Posted by the-one1 View Post
    If "IS" in so inferior, then why are cars and motorcycles still using that style mount? That's what I don't get.
    Most motorcycles use post mount style front brakes. I know my cbr does.

  9. #9
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    Quote Originally Posted by msrothwe View Post
    Most motorcycles use post mount style front brakes. I know my cbr does.
    I guess they're going that route too.

  10. #10
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    My preference is for IS since it's harder to strip the threads, and if you do strip the threads you're only out a brake caliper instead of an entire fork.

    Other than that I can't say I notice any difference between post and IS, I have the exact same brake mounted on a PM on one and IS on another of my bikes, they both work the same as far as I can tell. They both stay put and just work, no difference in maintenance, function, or anything other than the mounts.

  11. #11
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    Quote Originally Posted by aerius View Post
    My preference is for IS since it's harder to strip the threads, and if you do strip the threads you're only out a brake caliper instead of an entire fork.

    Other than that I can't say I notice any difference between post and IS, I have the exact same brake mounted on a PM on one and IS on another of my bikes, they both work the same as far as I can tell. They both stay put and just work, no difference in maintenance, function, or anything other than the mounts.
    Good point

  12. #12
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    Quote Originally Posted by aerius View Post
    My preference is for IS since it's harder to strip the threads, and if you do strip the threads you're only out a brake caliper instead of an entire fork.

    Other than that I can't say I notice any difference between post and IS, I have the exact same brake mounted on a PM on one and IS on another of my bikes, they both work the same as far as I can tell. They both stay put and just work, no difference in maintenance, function, or anything other than the mounts.
    Just to correct, if you happen to strip the threads of a IS mounted brake caliper, you'll simply wreck the adaptor and not the frame or brake caliper. Which means you just need another adaptor.

    I guess using a PM fork when running a 160mm front rotor is pretty good on saving the weight (and possible cost) of a IS to PM adaptor in between. Beside this, what I'm really wondering is why they make the calipers PM mount and the frame/fork IS ?? just make all frames PM instead... No point in making them IS anymore since you still have to get a PM adaptor to mount the caliper...

    One reason I'd guess would be the bigger margin of facing the pads perfectly to the rotor by having the opportunity to position the caliper in 3 different axis whereas PM mounts only allow for 1 axis... Which helps correct manufacturing alignment defaults.
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  13. #13
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    Quote Originally Posted by GTscoob View Post
    Post mounts are easier to set up ....
    Quote Originally Posted by mimi1885 View Post
    ...PM (74mm) are very practical, super easy to set up. ...
    I service and setup my hydraulic brakes for many many years and went through IS to PM. I absolutely disagree, that PM is easier to setup unless the setup is done by pressing the brake lever and tightening the bolts, that leads to non-parallel brake setup and squealing (e.g. how to force the pistons to pop up evenly, especially if there are 4 of them?; during tightening of the bolts caliper tends to twist). In IS system you need only to choose the right sized shims (thickness) and tighten the bolts, it can be done in 2 - 3 attempts or using the slide caliper even on the second attempt. Done. You can take off the caliper any time and keep the shims and mount it back in seconds, still parallel well. On the other hand proper setting of PM takes me at least 3 - 4 times longer playing with the caliper w/o pads and setting the gap evenly across the disc with "gap calipers" (translation only, I don't know the right english word, see the picture below) while alternately tightening the bolts a little and checking again. Pain in the ass. Once you take off the caliper, you can setup it again. I think the worst are Avids with dome-shaped spacers below and above the caliper, so the caliper can be tilted in 2 planes - virtually impossible to set up properly.
    Attached Thumbnails Attached Thumbnails Which front fork brake mount is better - Post or IS?-gap-calipers.jpg  


  14. #14
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    Quote Originally Posted by PeterG View Post
    I service and setup my hydraulic brakes for many many years and went through IS to PM. I absolutely disagree, that PM is easier to setup unless the setup is done by pressing the brake lever and tightening the bolts, that leads to non-parallel brake setup and squealing (e.g. how to force the pistons to pop up evenly, especially if there are 4 of them?; during tightening of the bolts caliper tends to twist). In IS system you need only to choose the right sized shims (thickness) and tighten the bolts, it can be done in 2 - 3 attempts or using the slide caliper even on the second attempt. Done. You can take off the caliper any time and keep the shims and mount it back in seconds, still parallel well. On the other hand proper setting of PM takes me at least 3 - 4 times longer playing with the caliper w/o pads and setting the gap evenly across the disc with "gap calipers" (translation only, I don't know the right english word, see the picture below) while alternately tightening the bolts a little and checking again. Pain in the ass. Once you take off the caliper, you can setup it again. I think the worst are Avids with dome-shaped spacers below and above the caliper, so the caliper can be tilted in 2 planes - virtually impossible to set up properly.
    While I understand where you're coming from in a mechanical sense of view, I've never had that problem with PM or IS. on both, I simply just squeeze the brake lever (I like to run 4 piston front and 2 piston rear), slowly tighten the bolts alternatively, and I usually have a near-perfect alignment, never had squealing or rubbing (unless the rotor is warped). For the record I have SAINT front brakes and XT or XTR rears, Fox post mount fork + IS rear.

  15. #15
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    Quote Originally Posted by David C View Post
    Just to correct, if you happen to strip the threads of a IS mounted brake caliper, you'll simply wreck the adaptor and not the frame or brake caliper. Which means you just need another adaptor.
    Well, that's true if you're putting a PM caliper on an IS fork using an adaptor. I kinda forget at times that nearly every caliper is PM these days. The brakes I have are IS mount on an IS fork on one bike and IS mount on a PM fork using an adaptor on my other bike. The latter is the worst of everything, it's possible to strip both the fork and the caliper if I do something stupid.

    Beside this, what I'm really wondering is why they make the calipers PM mount and the frame/fork IS ?? just make all frames PM instead... No point in making them IS anymore since you still have to get a PM adaptor to mount the caliper...
    I had a bike manufacturer rep tell me that they use IS mounts on their frames so that if someone Hulks outs while tightening the bolts they'll just kill a $15 adaptor instead of ruining the frame. It does add a bit of weight but it's cheap insurance to keep expensive parts from being ruined by heavy handed people.

  16. #16
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    can get all techy.. but all in all Post mount is going to give you a truer, quieter, lighter brake... If you over crank the bolts and strip the things you probably should have used a torque wrench...

    I've had both and will without a doubt say i can tell the diff between a post and IS mounting on the front... but as was mentioned I use Mech brakes which make the flexing more noticeable than a hydro brake will
    Going to try and bring Trail Tire TV back. go take a look... http://trailtiretv.blogspot.com/

  17. #17
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    Quote Originally Posted by aerius View Post
    Well, that's true if you're putting a PM caliper on an IS fork using an adaptor. I kinda forget at times that nearly every caliper is PM these days. The brakes I have are IS mount on an IS fork on one bike and IS mount on a PM fork using an adaptor on my other bike. The latter is the worst of everything, it's possible to strip both the fork and the caliper if I do something stupid.



    I had a bike manufacturer rep tell me that they use IS mounts on their frames so that if someone Hulks outs while tightening the bolts they'll just kill a $15 adaptor instead of ruining the frame. It does add a bit of weight but it's cheap insurance to keep expensive parts from being ruined by heavy handed people.
    Sounds like a good reason. I'm more afraid of cross-threading the bolt than over tighten them and strip the thread.
    Quote Originally Posted by NicoleB28 View Post
    topless. that's what all mtb girls do. we go ride, get topless, have pillow fights in the woods, scissor, then ride home!

  18. #18
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    Quote Originally Posted by GTscoob View Post
    Post mounts are easier to set up but IS mounts make brake pad swaps easier since you can just pull the mount and pull the pads out. At least this is the case with bottom loading brake pad designs. Top-loading calipers would be just as easy for both mounts.
    No need to take off the caliper to change pads. Just remove the wheel.
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  19. #19
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    Quote Originally Posted by photosheikh View Post
    Hi everyone.

    I just wondered what your opinion is on brake mounting standards.
    Which front fork brake mount is better - Post or IS?

    My reason for asking is that I may buy a 2008 Fox Talas front fork with IS mounts.
    My brakes will fit with the correct IS or post adaptors, but it seems that all the new forks are post mount.

    What are your experiences with the different mounts, any pros / cons...?

    Thanks for your advice.

    tBike
    Both IS and post mount work well.

    Which type a fork uses is low priority compared to most other features.
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