Hydraulics are skinny, most are 20-25mm from disc centerline to the outside. Mechanicals are wide in order to incorporate a pivot.
Oh, I know, just felt like adding something to the thread when really I had nothing to add.
Just humour me and we’ll both feel better 
I just ordered a set of Tektro Aquila from Crow Cycles, they’ll be here in a couple days, I’ll test fit them on my Oregon.
I got both a front and rear so I can see which adaptor works best.
Cross your fingers!
Ben, thanks for taking that risk. Aquila is the one I was going to try if nobody else had, but even better to get your report first!
-James
The Aquila is a No Go, it wasn’t even close, five millimeters of caliper hit the crank and that doesn’t allow for any free space, they are far wider than my Shimano hydraulic.
This is my last caliper experiment, I am not convinced that any mechanicals will fit, so far I have tried four different brands and they all fit just about the same, so I’ll let you all test out the other mechanical brakes.
Now if Roger can remember which mechanicals he tried that fit, well then…belly up to the bar, otherwise I am buying a set of hydraulics.
KH or Venture cranks?
KH Moments 150
I did a side by comparo with a KH frame and the spacing was the same. I also took a look at how a bigger disc (185mm) might work and the additional spacing from being set out 20mm further from the spindle only added a few millimeters.
You’d need a 200mm disc to even come close and then you’re talking about some ankle/foot strikes on the caliper. Maybe there is a mechanical caliper that is low profile, the QMD or whatever, but I’ve played with enough mechanical calipers at this point to know when I’m beat.
For sure a mechanical caliper could be designed to work, but I don’t think that is going to happen, hydraulics dominate the market, they work better than mechanicals, and they’re not expensive. The Tektro Aquila was nearly the same price as a set of Tektro Aruiga. And, the Aquila is really heavy!!
Oh, and in case you’re thinking: “why not flip it around and have the cable pull on the inside?” That clearance is already tight, 5mm between the spokes and the caliper.
Pics:
I have just been and checked. The model I tested with is a Miranda. This was the biggest of the 2 models I picked up (I don’t have the other one here so I can not tell you model or make on that one). It is 39mm from disc to back of calliper and it is 41 from disc to the back of the venture cranks.
I can see why you can not get yours to fit with the KH cranks on.
Roger
Ben, are you using spacers on the cranks? If so what size?
Hmm, bummer. I don’t see how spacers could fix that, it’s just too much overlap, spacing out the crank far enough would lead to slop at the crank splines.
Hydraulic disk brake choice?
OK, so having basically ruled out mechanicals, what’s the best reasonably affordable hydro caliper?
I think they are 2mm, might be 4mm, same on my KH 29er, but even if you used a 6mm spacer the caliper would still not clear. The mechanical calipers are so much wider than hydraulics, it’s not even close in comparison.
Best bet on inexpensive hydraulics is Tektro or Magura, that way you can use mineral oil and they both allow easy bleading so shortening the hose is no problem. I have the Bengals that came with my Oregon, I’ll sell it cheap if someone wants it. It is brand new, I’m just not into white 
I’m using a Shimano SLX, works very good (with MountainUni external disk and now with my custom internal one).
Only thing i changed: the brake pads. Im now using Koolstop (better lifetime and brake power than the original Shimanos)
I have been looking at disc brake options, something inexpensive, mineral oil, easy to bleed/shorten lines, durable, aluminum lever:
This one is on sale, I just bought two sets, comes with the rotor (rotors are not cheap), but needs an IS adaptor (I had a couple adaptors sitting around):
Here’s an inexpensive IS adaptor for the above:
Or get it complete and spend more:
Or get it in white and be “the boss”:
Chain Reaction Cycles only has ten pairs left of the 2009 Tektro Aruiga, so order soon if you want a set. You do need a 160mm IS adaptor, but they’re cheap, most LBS should have spares and might even give them to you for free!
If you order a disc brake, keep in mind that some don’t come with a rotor, so add that cost…
The Aruiga comes with a rotor for $50 plus ~$8 shipping, add another $6 for the adaptor if you need it, still a whole lot less than $98 for a complete 2010 Aruiga, and a whole lots less than other choices.
You don’t need much brake to stop a uni, even a wimpy disc brake is stronger than a Magura on it’s best day. Disc brakes don’t get overheated like they do on bikes, so a small disc is both lighter and more durable plus it places the caliper further from the ground and your feet.
I run an inexpensive Shimano M535 160mm on my Oregon and it’s more than enough.
Also, when ordering a disc brake, look at the angle of the line as it leaves the reservoir, some angle down steeply which could complicated cable wrapping/routing.
I am so ready for disc brakes on my 29 and 26, it has been rainy and slimey here for months!
Ben, thanks for all the info you add to these threads, I for one really appreciate it.
So, when we’re looking for a disc brake, is there a consensus on whether we should be going for front or rear, or does it not really matter?
FYI, the 2010 (but not 2011) Magura Marta disk brake is compatible with the Spooner. This is the only Spooner-compatible disk brake that I know of. I’ve been running this brake as one of my disk brake options for about a year and it works well. May be hard to find, though.
Kris
For other disk brakes, a universal KH brake lever extension will be available by June.
Good to know Kris about a somewhat universal handle mod for spooners. I’ve been lopping off the nub on many hydraulic handles, and have heard of very few where this isnt required. Im suggesting Shimano, Quad Dime, Gusset and Formula RX, and Hope for those wanting brake bling.
Sorry, I meant to post that info. So you are looking for a front brake for two reason, one is that the line is shorter so you probably won’t have to cut it, two you need the front brake I.S. adaptor to fit the D’Brake from Nimbus.
More info on disc brake standards: there are two standards, the 51mm IS and the 74mm post mount. All of the current disc brake calipers have the mounting holes spaced at 74mm, which works for direct mount to some mtb forks and frames. But, for the remainder, the calipers must be reduced to a 51mm I.S. (International Standard) us a caliper mounting adaptor.
If you see a brake advertised as “post mount” and it is not shown with an adaptor, then you need to buy one as an additional cost. There are also post mount adaptors, you don’t want those, you want the I.S. adaptors for the rotor size you choose, so 160mm, 185mm, 210mm, etc…
Disc brakes use two kinds of fluid, mineral oil and DOT. Mineral oil is oily, buy wpn’t eat your paint, whereas DOT is a solvent. I prefer mineral oil, but DOT is fine, esp since DOT is what is used in motorcyle and automobile brakes.
Hmm, what else, well, like Kris wrote, the sponner is not a great fit for all brake levers, so you can trim the lever, wrap the spooner in tape, or use a heat gun to distort the lever to fit. KH has a new universal spooner coming out, I’ll probably wait for those and make due with the others for now.
Avoid carbon brake levers as they are fragile, avoid ultralight brakes and custom machined brakes that would be expensive to fix if they broke. Simple is better when it comes to brakes.
Magura makes some decent disc brakes, Martas are often on sale and not too expensive, maybe $100 a set. Kris is using the Marta, so it must be worthy 