I inherited my brothers Inbred and I've decided to fit discs front and rear. On the back is an IS disc mount but because it has sliding mounts, it needs special drop-outs to fit the calliper properly. Trouble is, it seems I can only mount the calliper inside the rear triangle instead of on the mounts, according to On-One. Has anyone got one of these and managed to sort this problem out?
What brake? Some can be problematic due to restricted clearance. I presume you've got the "slot dropout" back end like this [img] 
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No, mine (I think) is the earlier type, it has bolt-on drop-outs on either inside to take a standard axle, but the IS mounts are on the frame
[img][url= http://farm6.static.flickr.com/5079/5908275216_65142955d6.jp g" target="_blank">
So that's much more like a "standard" IS mount, although with that adaptor you'll be needing a dinner plate for a rotor! Unless it's a tandem or you're VERY heavy, then a 160 rear brake should be fine.
With your frame the brake goes outside the rear triangle, not inside it as per the photo I posted... Not sure what your problem is, sorry!
On this photo you can see the actual hangers which take a standard 135mm axle, on the inside of the frame. The gap you see between the calliper and frame is the difference in frame width and axle width, about 5mm.
[img][url= http://farm6.static.flickr.com/5073/5907871799_5fbcbb9c45.jp g" target="_blank">
My problem is that, from the factory, you cannot just bolt on an IS calliper, you need a spacer. I had an email from On-One this morning telling me that is how it is, so I either have to fabricate a bracket to fill the gap or mount the calliper in the frame, which I don't particularly want to do.
Oh, at the moment it has 203's but I've got stuff coming to fit a 180 I already have.
The "spacers" were 6mm thick aluminium washers.
Some regular M6 washers (three or four of them) will do just the same job, or a drilled out M6 nut.
That's what I thought of doing, niggling doubt about any flex through the spacer.
You could use two adapters, & just get one machined down to the thickness of the gap, but I'd go with a 160mm disc & pack it out with washers. I've done simillar in the past without any issues.
spacing it in 6 mm will be no great issue.
You can also get spacers to space the disc out should you prefer
Managed to get 10 M6 washers and 4 M6*25mm bolts from a hardware shop for only a quid! All built up, not impressed with the cobbled together look but I'm back in work next week so I'll knock up some proper spacers.
Not pretty but does the job:
[img][url= http://farm7.static.flickr.com/6042/5908628330_862b94c4fe.jp g" target="_blank">
[/url] by [url= http://www.flickr.com/people/8129237@N02/ ]supervee_2000[/url], on Flickr[/img]
Will sort out something a little neater next week.
Well done - happy skidding 🙂