Discs aren’t my stoppers of choice and I’m as technically gifted as my tortoise but I’m fitting Hope mono mini brakes on my new Karate Monkey frame. That has 51mm IS disc mounts front and rear, the front went straight on but the rear the caliper fouls the frame. If you click on the link and enlarge the bottom right pic the body of the caliper fouls the bar between the holes? Does that mean I need an adapter or will it never fit?
http://surlybikes.com/bikes/karate_monkey

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Looks like you’ll need an adaptor and the next size up disc.

What sort of adapter. I know nothing…………….

If you already have a 160mm disc you will need a 180mm disc and 180mm IS to Post Mount adaptor.
Another possible fix would be to add a link to the chain and run the rear wheel further back in the drop outs and the caliper further back in the mounting slots.

The problem is I can’t fit both bolts, no matter where the wheel sits. I have a 140mm rear.

Substitute the 180s in my last post for 160s. 140mm is smaller than most folks use these days, particularly on a 29er.

As above 140 is too small

You need an IS to IS +20mm adapter and a 160mm disk

Just checked your first post and I could be wrong about the adaptor. The Mono Mini is an early brake and most likely IS mount. If so you will need a +10mm IS to IS adaptor, although this may also foul the frame mount. In that case you will need a new caliper for the brake.

Right, thanks guys. I have a borrowed IS to IS adaptor on the way and I’m just off to buy a disc.
I have the physique of a racing snake, I can stop dead on V brakes…so any disc is overkill for me………