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  1. #1
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    Use XTR 140mm discs in a 160mm setup (no adapters) - is it possible?

    My current setup is 160mm XT CenterLock discs, with BR-M765 calipers.
    Front is Postmount and rear is IS2000.

    Can I simply use XTR 140mm CenterLock discs with my current setup? What if I just put the discs in, without any adapter?
    Upon my calculations the braking surface (contact pads-disc) would be reduced to ~70%. Is there any drawback to this, except a decrease in braking force?

    I intend to build a second set of wheels, for road use only, and the XTR discs will allow me to loose some weight. And I wouldn't mind the lower braking force .

  2. #2
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    If I understand you correctly, then what I think will happen is you'll get an odd 'V' shaped wear pattern, which will develop rapidly, and quickly the "good" part of the pads -- the portions not contacting the disc surface -- will meet when the brake is actuated, eliminating any braking force.

    It'd be interesting to try if you have the rotors laying around, but I'm nearly certain you'll go through pads like mad and the braking action will start out poor, then turn non-existant.

    Please update this thread if you try it.
    speedub.nate
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  3. #3
    Nightriding rules SuperModerator
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    I agree with Nate... you will eat pads like there is no tomorrow.. and might get some squealing and other undesired behaviors.... the 140mm adapter for the rear is like 10 bucks (and you probably already have it as you run the front with no adapter )
    I would keep the front at 160mm...weight savings are small between 160 and 140..they exist but they are small..

  4. #4
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    Well I see your point here.

    Indeed the weight difference is quite small, 111g vs 156g per each rotor, so using an adapter would make no sense - it would simply add up to the same weight or even more.

    I don't have the 140mm discs so unfortunately there's no way to test before ordering.


    But then, there are a few things I don't get:
    - How do you run 140mm on front if the caliper uses no adapter? Is there a different caliper for 140?
    - Same question for rear: never seen an adapter IS2000 to Postmount 140mm for rear.
    - This puzzles me as I always was under the impression that there's one type of BR-M765 caliper - are there in fact different calipers for 140 and 160mm?



    Quote Originally Posted by crisillo
    [...]and you probably already have it as you run the front with no adapter [...]
    How's that?


    I was in fact looking for:
    - the ability to change from MTB wheels to road quick - no fiddling with adapters or anything else
    - shave off some weight. The smaller discs sounded like a good and simple idea. The price difference between the XT and XTR rotors was resonable, also.

  5. #5
    Nightriding rules SuperModerator
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    Quote Originally Posted by ovidiugm
    Well I see your point here.

    Indeed the weight difference is quite small, 111g vs 156g per each rotor, so using an adapter would make no sense - it would simply add up to the same weight or even more.

    I don't have the 140mm discs so unfortunately there's no way to test before ordering.


    But then, there are a few things I don't get:
    - How do you run 140mm on front if the caliper uses no adapter? Is there a different caliper for 140?
    - Same question for rear: never seen an adapter IS2000 to Postmount 140mm for rear.
    - This puzzles me as I always was under the impression that there's one type of BR-M765 caliper - are there in fact different calipers for 140 and 160mm?
    in the front I think there is no way of running a 140mm.. the PM is made for 160mm... if you look shimano specs the 140 as a rear rotor only....you are correct there is only one caliper (160mm postmount), see below on how to run 140mm in the rear...

    Quote Originally Posted by ovidiugm

    How's that?


    I was in fact looking for:
    - the ability to change from MTB wheels to road quick - no fiddling with adapters or anything else
    - shave off some weight. The smaller discs sounded like a good and simple idea. The price difference between the XT and XTR rotors was resonable, also.
    any IS to PM adapter will allow you to run a 20mm smaller rotor than in the front when used in the rear (and viceversa), so your 160mm front adapter...is also a 140mm rear...

    Last edited by crisillo; 05-16-2007 at 02:19 PM.

  6. #6
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    Quote Originally Posted by ovidiugm
    - How do you run 140mm on front if the caliper uses no adapter? Is there a different caliper for 140?
    - Same question for rear: never seen an adapter IS2000 to Postmount 140mm for rear.
    - This puzzles me as I always was under the impression that there's one type of BR-M765 caliper - are there in fact different calipers for 140 and 160mm?
    Here's the deal.

    The BR-M765 is, natively, a 74mm post mount caliper. It will bolt right up to a Manitou fork, for instance, and fit a 160mm rotor. Caliper and bolts, no added parts needed.

    To fit a 51mm IS fork, you'll need a front adapter. 160, 185, 203mm, etc.

    (It's worth noting that a front 160mm 51mm IS adapter duplicates a 74mm Post Mount fork. Post Mount fork = fork w/ IS tabs & Front 160mm adapter. Stick a caliper to it, it's done.)

    To fit a 51mm IS frame (rear), your need a rear adapter. 160, 185, 203mm, etc.

    To use a 140mm rotor on the REAR, you'll mount it up using a 160mm FRONT adaper. There is a 10mm offset between front and rear IS standards, half the difference between 160 and 140.

    (This is how Hope used to get away with making just one IS-mount Mini caliper, using 160mm rotors for front applications and 140mm rear applications.)

    speedub.nate
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  7. #7
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    Oh now you're talking! I start getting the hang of it
    --------- goes back and reads previous two posts again --------

    Well, seems that there's not much I can do. And because my fork is postmount too (Manitou, indeed ), I don't even have the 160 front ( = 140 rear) adapter referred above - this was confusing me.

    So no way to run 140 / 140. Hm. Maybe I'll just change the adapter in the rear and build both sets of wheels with 160 / 140...I just have to think about it...however, thanks all for your explanations!

  8. #8
    Nightriding rules SuperModerator
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    Quote Originally Posted by ovidiugm
    Oh now you're talking! I start getting the hang of it
    --------- goes back and reads previous two posts again --------

    Well, seems that there's not much I can do. And because my fork is postmount too (Manitou, indeed ), I don't even have the 160 front ( = 140 rear) adapter referred above - this was confusing me.

    So no way to run 140 / 140. Hm. Maybe I'll just change the adapter in the rear and build both sets of wheels with 160 / 140...I just have to think about it...however, thanks all for your explanations!
    glad you got it sorted... sorry about the confusion.. I assumed that your brakes came with both adapters (as when you buy them separately.. I suppose you got yours with the bike already, or your shop kept it )

    yeah.. going 160/140 is a very viable option (reducing expenses too )

  9. #9
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    Yeah my bike came stock with the brakes - therefore the missing adapter .

    I just posted to weight weenies section too - maybe someone over there would be able to recommend me some light 160mm rotor to really make a difference.

  10. #10
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    07 shimano makes 3 calipers in xtr 140r/160f, 160r/180f, and 160r
    they all work as listed without adaptors in IS. if you have IS on your fork I dont think there is any way to go 140

  11. #11
    Nightriding rules SuperModerator
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    Quote Originally Posted by ovidiugm
    Yeah my bike came stock with the brakes - therefore the missing adapter .

    I just posted to weight weenies section too - maybe someone over there would be able to recommend me some light 160mm rotor to really make a difference.

    You could go with Alligator/Ashima serrated rotors.. they are a bit lighter than "standard ones", the 160mm that I use in the rear came in at 96g, but I think you have centerlock hubs, so you would need to add the weight of the adapter..... an alternative can be something like Stans rotors...but performance won't be the same... I ahven't felt much difference in power with the serrated rotors

    this is a pic of my 203mm (155g)

    front serrated rotor

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