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XTR Front Caliper: ISIS to Post Adaptor

Titanium Rocket

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Difficult to keep this one simple, but here goes:


1.  My old Fox fork had the ISIS mount, so I have an ISIS mount XTR caliper which fitted and worked perfectly.

2.  Recently acquired a new Fox fork, but with a Post mount for the brake caliper (apparently the more popular system these days). The LBS gave me the appropriate XTR adaptor for a 120 mm rotor; with a few shims, I got it all fitted fine.

3.  Now after 6 months of use, and I see that the pads are only making +/- 80% contact with the rotor; the outer 20% of the pad is totally un-touched.

4.  The adaptor is obviously setting the caliper too far away to make full contact with the rotor. I have checked: it is the right adaptor for a 120 mm rotor. Also, there are no superfluous washers setting it too far out.


I can actually feel that my front brake power is poor. Does anyone have any ideas how I can claim my un-used 20% of potential stopping power:

1.  I could file down the post mounts on the fork (obviously highly dangerous).

2.  My LBS says "...just buy a new XTR post-mount caliper..." (easy for them to say).

3.  Or I could go to an engineering shop and get them to make a precision adaptor (will be costly).


Has anyone experienced this problem? JB - any ideas?
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I take it you mean 160mm rotor? First question; it shouldn't matter but, is the adapter a genuine shimano adapter or a 3rd party adapter? In my experience some cheap 3rd party adapters etc are seldom manufactured to IS specs.

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You do not get a 160mm to 160mm IS to mount adapter. You will have to get a A2Z adapter that will make you use a 180 front rotor.

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I recently changed from a Suntour fork to a Fox and had to get an adaptor to fit the XTR caliper. Shimano had none in stock and aparently don't make an adaptor for a 160mm rotor (that may have changed). You have to change to a 180mm rotor and I managed to get a Hope adaptor and 180mm rotor which solved my problem. But the excersice was not cheap.

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Thanks for the contributions. Summary:


1. I did mean 160 mm rotor...nit.

2. Have been told by our local Shimano agent that Shimano don't make a 160 mm adaptor for this. Believe I have a generic one.

3. Appears the only way is to change to a 180 mm rotor, and shift the caliper outwards by adding washers / spacers, until it matches the diamter of the rotor.

4.  Am a very fussy fellow...possibly rather just buy the correct Post-mount caliper....and do the job properly.  
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CRC have a special on a XT caliper for R630, post mount. I bought a XTR caliper from them for only R370...

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  • 2 weeks later...

I have the exact same problem - KNC & A2Z Adapter were supposed to work with a 160mm rotor, I can confirm that it does not work.

Adapter and 180mm rotor the only way to solve the problem!

On my way now to buy a 180mm XTR Rotor (R600) eish....

You also cannot seem to get postmount XTR break system from Shimano, you have to wait 6 weeks!!!


sharkysa2009-06-05 04:28:00
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Sharkysa, you are on the money. Neither th A2Z or KCNC adaptors align the XTR 160 mm rotor properly, you must increase to a 180 mm rotor.


I have decided to go the other way because I want to eliminate the chance of a misfit forever: I have bought a XT post mount calliper. Only R200 more than an XTR 180 mm rotor you are talking about. Post calliper for Post fork - no more incompatibility, end of story, sleep tight.
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That's the best solution! But I will now have some serious breaking capability on the front.....plus some extra grams!

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