I know there was a thread about this recently but my question wasn't really answered by it.
I've got on old Orange E8 frame / Rock Shox Duke with Hope mini IS mount front & rear, running 180mm rotor front & 160mm rear.
New bike has post mount Rock Shox Reba & IS rear. The rear brake has an IS to post mount adaptor fitted already to fit the existing Elixir R
So my question is, what do I need to transfer the brakes to the new bike? I assume a post to IS adaptor for the front? New disc (most of the adaptor's seem to increase disc size by 20mm)? So I guess a 200 / 203 mm front rotor?
Is there a mount adaptor that does IS to post mount but doesn't increase by 20mm? Forks are OK with rotor up to 205mm so I shouldn't have an issue there,
For the rear, should I be able to fit my Hope 160mm IS to the IS mount that's already on the frame?
Confused from Central Scotland needs your help,,,
The rear will just bolt on without an adaptor, so yes.
The front was covered in that other thread, I though someone did post up an adaptor that didn't have the 20mm increase.
You can't engineer a 180mm is calliper into the space on a post mount without having to move it out a bit hence the extra 20mm: you'd have to go up a rotor size. If you like a bodge you can space the post mount adapter out from the fork slightly with washers to fit a 203mm rotor in it, as 200mm is herder to come by. Formula do one but the rrp is frankly ridiculous.
Or if you are confident (really confident!) with brakes, try buying an old 160mm mini and either use the whole caliper or dismantle your brake and use just the half with the mount on it, plus the is to post mount adapter and keep you 180mm rotor. You used to be able to buy half a calliper for changing rotor sizes.
Rear
Caliper will bolt straight to the frame, no adapter needed.
Front
IIRC With the minis, to change disc size you had to un-bolt the two halves of the caliper and swap the half with the mounting bolts for a new caliper half to get the different mounting positions (then refill and bleed!). Think you are stuck with the Hope adapter to convert IS to post mount, but as you say that also comes with the +20mm issue. May have to swap the caliper half to a 160mm, to give 180mm when you add the Hope Post to IS adapter. It could be easier and no more expensive to buy a post mount brake from the classifieds online margins. I was completely underwelmed with my first disc brakes (Hope Minis), whereas Hayes 9, Avid Juicy, v cheap now and night and day difference in power compared to the original Minis.
Thanks for the suggestions so far,
I've found this old thread [url= http://www.singletrackworld.com/forum/topic/hope-post-mount-to-is-fork-adapter-sanity-check-please ]about the same issue[/url]
Any thoughts on Stato's suggestion re a rear adaptor?
G
Didn't we establish on one of the other threads that you need one of these ?
https://clee-cycles.co.uk/cc/catalog/product_info.php/cPath/21_123/products_id/989?osCsid=8nmp2rm7o3n5iv33teveoskte2
Disc calliper adapter to mount a 160mm IS calliper on a post mount fork with a 160mm disc.It may not fit all callipers to all forks as there is very little clearance on some designs! If it does not fit - it can be returned.
Will also fit a 180mm IS calliper to a post mount fork with a 180mm disc, or a 200mm IS calliper to a post mount fork with a 200mm disc. You do not have to go up a disc size.
Didn't we establish on one of the other threads that you need one of these ?
https://clee-cycles.co.uk/cc/catalog/product_info.php/cPath/21_123/products_id/989?osCsid=8nmp2rm7o3n5iv33teveoskte2
Just got one of these today and it certainly seems to work fitting an IS XTR caliper to a Post Mount (Fox) fork without changing the 160mm rotor size..
[img] 
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(sorry about the image quality.. only had my phone to hand)
Many thanks to Ant at XC Racer for confirming it was what I wanted and ordering it in even though they don't do them any more..
Apparently the ones for larger discs just use spacers to pad it out.
Frogstomp, I bought the same one and the adaptor fouls the fork leg on my Revelations, so I had to use the spacers. It's the spacers that add the extra 20mm, not the adaptor itself!
I was wondering if I could file it down a bit so it would fit like that, but I wasn't sure it would work. Thanks for the pic, I think I'll give it a go now!
PeterPoddy.. I can see how that would be - it was very tight on the Foxes..
Could you not just put a very thin washer between the fork post mount and the adapter? It may push it out enough to get clearance and hopefully the fractional movement of the caliper won't be too detrimental..?