Hi there, I tried with the search function but was unlucky 
Anyone tried to mount a 140mm disc rotor on the KH Spirit Cranks?
I’d like to build a 29" (and maybe a 36") with Spirit Cranks and external disc and I wonder if a 140mm will fit or not…
Hi Mutaito,
the official documentation for KH Spirit cranks refers to 160 or 180mm rotor. I know that NurseBen was running 200mm rotor on some of his unis.
You can try and check the disc brakes thread. However, 140mm doesn’t ring a bell.
You will also need to have the proper IS adapter to be sure your caliper seats close enough to grab the braking area properly 
I scrolled the disc brake tread with no result…
My suspect is that using a 140mm rotor, the caliper will hit the crank, but I’d like to be sure about it
Which doesn’t exist. The positioning of the IS holes on both KH frames and D-brake adapters conforms to the front brake standard, adapters for which will only allow a 160 disc at smallest. You can run a 140 disc using the same adapter on rear mounts which are 10mm closer to the axle (as I do on my bike, which has 160 front, 140 rear with the same adapters both ends), but that’s not what we have on a uni.
I’m actually using an IS mount caliper on my uni, so no adapter, with a 160 disc - it would be impossible to fit a caliper closer in than that, with or without an adapter.
Not that I’m sure what the advantage of a 140 disc is - despite clearly being a fan of having parts as small as possible (very few people even run a rear 140 disc on a bike) I seriously considered going 180 on the uni as the way we use discs tends to dump a lot of heat in them - mine certainly make noises which suggest they’re getting pretty hot and start to fade on occasion.
Thanks very much Aracer! This clear everything 
Advantage of a 140mm disc? Smaller rotor is less exposed to damages on UPDs and (very slightly) less rotating mass weight.
140mm disk can only be used on rear, dimensions of a disk brake tab on a rear and front brake are different. Unless you make your own disk brake tab, you will not be able to fit a 140mm disk. KH frames and Nimbus D-brake adapter are made to be used with a front brake.
Maybe when using a bunch of spacers but it will be a pain.
Edit: I didn’t see Aracer’s reply. He’s right!
Don’t worry about hitting the rotor, it won’t happen, I have had too many UPD’s to count, and my rotors are straight.
With a 140mm rotor, assuming you can find a high quality one, you will save at best 5-10gms, so not exactly a significant weight savings, esp since it’s so close to the hub that it really won’t contribute anything to rotational weight.
And like Jacob suggested, I don’t think you can get an IS adaptor that’ll work for a 140mm caliper setting.
Also, I think you’ll have clearance issues between caliper and crank, it’s close enough with a 160mm; crank spacers and caliper brand will make a difference.
If anything, I’d say stay with a 160mm or even get a 180mm.
There’s no need for a 203mm, though I have three 203mm rotors if someone wants one 
If you’re concerned about cutting rotational weight, you’d better get a TI hub: http://www.unicycle.com/unicycle-hardware/hubs-and-hub-assemblies/impact-exceed-titanium-hub.html.
Bad fall during a technical DH, the rider hit the rotor on a northshore, bend it 90° and we had to break it so we could continue riding…
thats a floating disc and must have been a big hit and unluckily at a bad angle to pop it out. Doesnt appear to be a Hope so quality is questionable. The clarks ones are terrible imo
Re: 203mm
I run 203 on 36er touring 29er Xc and 26 Muni. I find it gives a nicer feel with hydro’s because the brakes work too efficiently for one wheel.
Recently did a XC half marathon and some stupid descents!!! massively long and steep. One guy cooked a bikes brakes and crashed out at the bottom.
My 203mm Xt ice rotor and xt front brake worked perfect. Zero fade and runs true. Dry or wet never a sound. Simply great brakes from Shimano
140mm? there are some amazingly light one piece ss 160mm rotors pretty cheap. I have never hit a rotor yet. Being outboard doesnt really make it much more exposed than a bike disc. likewise for example i have never hit the front rotor on my bike far as i can recall.
all the best. Happy trails
I’m not as lucky as you are: my magura 160 and 203 storm rotor (2mm plain steel) aren’t straight anymore since first or second ride…
Had chosen 203mm for mad4one inboard mount caliper clearance issue in my 24".
I have a 180mm disk on my Muni, on Spirit cranks. My disk is really out of true, but it’s easy to pull back. I’m probably going to change my disk(s) on all my setups for fancy floating disks, hopefully they’ll stay straight for longer.