I am thinking about adding disc brakes to my 24" muni, and I am curious as to what the advantages/disadvantages are to hub disc vs crank disc brakes.
Any help is appreciated, thanks!
-Dane
In my opinion the most important reason for outboard discs is Schlumpf compatibility, otherwise I would use inboard discs which allow for a variety of different cranks, easier swapping of cranks and better protection for the disc.
I have the QX Series Zero-Q cranks on my 24 inch muni and prefer them over the Spirits on my 26 Guni.
I’m hoping that in the future the Schlumpf hub will include an option for inboard disc like the 14-geared Rohloff speedhub or the JR Drift Trikes 3.8:1 hub.
The outboard allows you to keep a maintenance friendly and stronger undished wheel. As much as you think you might hit your ankle with the disc, you would have to be mid UPD to do so and then inboard/outboard wouldnt matter. It kinda works with the schlumpf hub (if you like loctite and precise torque settings) however the next generation of schlumpf will likely be redesigned to work with disc brakes. Swapping to different length cranks isnt that bad as long as the cranks have a rotor attached already.
The inboard allows you to choose different crank arms (other than spirit or sinz), has more width for callipers (width is a massive factor in calliper choice) and keeps the brake slightly further away from your feet.
If you want an inboard brake, you really need to buy with one… the hubs are pricy and the wheel would need to be rebuilt completely including new spokes. Outboards are much more friendly for retrofitting down the line.
When taking the wheel off a uni with disc brakes, loosen the calliper from the standoff slightly. When putting it back in put the bearing housings on, squeeze the brake lever to centre the calliper over the rotor and then tighten the calliper onto the standoff. It helps to have a long T head 5mm hex key for outboard brakes as a regular key cant reach in to loosen the beaing housing.
Can you use the d-brake nimbus clamp with KH spirit DH cranks? Or do you need a frame with welded mounts for spirit DH cranks?
Thanks for all the great info guys.
d-brake works just fine with any frame and spirits
Sure!
I think the biggest reason to go with inboard over outboard is crank choice. It could be very annoying to be stuck with only being able to buy KH spirits (or sinz).
On the other side of the coin, outboard is much simpler to set up as it doesn’t require a new hub/spokes/wheelbuild. Also, non symmetrical wheels are weaker and more difficult to build.
Does the placement of the caliper make much difference? nimbus bearing mount vs a frame welded mount? Wondering if you’re more prone to ankle smack the caliper with the nimbus mount. Or if smacking a caliper with your ankle is better than smacking the (possibly sharp) disc, ouch!
So the list so far:
Inboard Disc Brake
Pros:
-Disc is more protected from damage
-Rider is more protected from ankle strikes
-More crank choices
Cons:
-Requires asymmetrical wheel build, which is weaker than a symmetrical wheel build
-More difficult wheel build
-Requires special hub with disc attachments
-Not compatible with schlumpf geared hub
Outboard Disc Brake
Pros:
-Simple Setup
-Maintenance friendly
Cons:
-Restricted to KH spirit or sinz cranks
-Rider is more prone to ankle strikes
-Disc is more prone to taking damage
Wheel dishing is one of the reasons that I don’t build my own wheels (that and pre built, ‘package’ unis are much cheaper). As for strength, however, you’d be surprised at how strong a dished wheel can be. That said, I’m not a very hard rider, but I’m still pretty rough with my 29er and despite numerous bad landings it’s stayed true (although I did once have to tighten a couple of spokes).
I’m not that convinced how major those issues are. Of course both are more likely with an outboard disc, but are either actually all that likely to happen even with one of those?
as soon as you put disc brakes on your uni your life will change in two ways. You will love riding when everything works. When there is something wrong with the brakes you will hate life.
Out vs inside brakes are just a preference besides to those who use a geared hub. Id personally use a disc hub so I can change cranks out faster and easier. Kris makes the toughest unicycle products on the market, they withstand the trails he test them on. Those trails are the meanest trails I have ever ridden. Both internal and external disc do totally fine.
Good luck 
With me it’s likely! I seem to enjoy to smash my ankles around. I blame it on my bad shoe soles though 
Inboard, con
One more con to inboard (hub-mounted) disc is the bearing must be removed in order to replace a broken spoke on the disc side.
This is not necessary with outboard (crank-mounted) disc.
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How does the list look now?
Inboard Disc Brake
Pros:
-Disc is more protected from damage
-Rider is more protected from ankle strikes (minor)
-More crank choices
Cons:
-Requires asymmetrical wheel build, which is weaker than a symmetrical wheel build
-More difficult wheel build
-Requires special hub with disc attachments
-Not compatible with schlumpf geared hub
-Disc and bearing must be removed to replace broken spokes, disc side
Outboard Disc Brake
Pros:
-Simple Setup
-Maintenance friendly
Cons:
-Restricted to KH spirit or sinz cranks
-Rider is more prone to ankle strikes (minor)
-Disc is more prone to taking damage
I think you are giving too much value to the speculation of more ankle strikes. If this was a real problem on crank mounted discs it would be the same problem on every bicycle. People aren’t banging their ankles against their chanrings, and I suspect that the same is true for crank mounted discs.
If you are including the Sinz cranks, then you are also including every ISIS crank made that accepts a 110mm bcd chainring. The MountainUni disc will fit any 110mm bcd crank arm, including square taper. FMF made a junior crankset that can be had pretty cheap and had short lengths available.
If the inside disc is protected from damage at all it is only because it is closer to the center line of the wheel, and not because it has a bit of frame separating it from the rider. That little difference could be a factor, but I think a small one. The asymmetric wheel would have approximately twice as much tension on the disc side of the wheel, and that is significant. If you have the right spokes it is no harder to build a disc wheel than a symmetrical wheel.
Since you can use any rotor on an inside disc wheel or Spirit cranks you have the ability to move the caliper further from the spindle. This means that you can use a bigger variety of calipers to take advantage of the extra space available. It also means a bigger rotor which is more prone to hitting things. So nothing comes without some trade off.
So, in my opinion, your list would read more like:
Inboard Disc Brake
Pros:
-More crank choices
-More brake choices
Cons:
-Requires asymmetrical wheel build, which is weaker than a symmetrical wheel build
-Requires special hub with disc attachments
-Not compatible with schlumpf geared hub
-Disc and bearing must be removed to replace broken spokes, disc side
Outboard Disc Brake
Pros:
-Simple Setup
-Maintenance friendly
-Spirit cranks allow different rotors, and maybe more caliper choices
Cons:
-Restricted to KH spirit cranks w/ any 5 bolt standard rotor
-or MountainUni rotor w/sinz cranks, or any ISIS 110mm BCD crankset
The main advantage and why i only have inboards is crank choice. Though spirits are very good, i dont want to be limited to them.
Are the challenges when riding a bike similar enough to the challenges faced when riding a uni? I think the concern would be what happens during a UPD, not for general riding. After all, for general riding you’d strike your ankle on the crank long before you’d strike it against the outboard disc rotor.
Taking away the bike/uni comparison I’d make a slight modification… Are people banging their ankles or bending their rotors when riding unis with outboard rotors? So far I haven’t heard of (m)any cases and if it were a problem I’d like to think that I would be hearing all about it on this board.
i saw a picture of a smashed hope rotor somewhere here i think but that was bent against a rock and then brute force removed to continue a ride.
I’m sure that there have been bent rotors. That happens on mountain bikes too. The question is whether or not it is more likely with the disc mounted inside or outside. A question that will likely never be answered with data.
That little bit of rotor that might be covered by the frame tube isn’t very exposed anyway, and the bit hanging down below the frame is almost just as exposed inside or out.
Like many things this debate will come down to preference more than anything. I think there are real reasons to prefer one over the other, and the list that Dane started seems to be pointing to that.
It’s just a footnote to the topic of this thread but if you ride a freewheel unicycle your only choice is inboard, naturally.
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