Picked up an old Trek 9.8 carbon mtb yesterday, it has V brakes currently but thinking of putting on some nice disc brakes and wheels I have. The front SID forks have disc mounts too so that's okay but looking at the rear of the frame, it has hose guides but not an obvious mounting place. There's two lower down holes by the rear dropout (as well as rack eyelet), so I'm presuming there must be some kind of weird size mounting bracket you could get that would do the job? Anyone know for sure, size and where from? Cheers
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You can get disc mounts for non disc bikes (wiggle have one, do a search). They generally don’t work very well (forces applied by the disc are stronger than the grip on the frame), so generally pretty poor. I wouldn’t bother.
The A2Z disc mount isn't great as it doesn't have a torque arm so isn't great against the twisting forces. I've got annon disc frame I've been running with an aftermarket disc mount that has worked well so far. I'm selling it shortly as I wanted a disc frame that I could run a kids trailer with and it wouldn't fit with the disc adapter.
https://www.tensile.net/tensile-disc-brake-converter.html
If you're interested I'll probably sell it for £20 delivered UK. But, I'm not sure if I'd use it on a carbon frame as it needs at the minimum the grub screw up tight against the frame itself to brace the lower part of it. Ideally you also tap a hole in your dropout (I didn't do this and it worked fine without - it's the torque arm to the brake boss that does most of the bracing)
http://forums.mtbr.com/trek/need-advice-trek-9-8-disc-brake-mount-863826.html
Looks like trek make a mount that uses the large holes either side of the rack mount
Thanks for lead orangeboy - found one here https://www.tritoncycles.co.uk/components-c9/disc-brakes-c58/trek-fisher-01-new-intl-disc-mount-p12568
cheers!