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Discussion Starter · #1 ·
Hi guys, first time posting though I've been using this forum as a great resource for years!

I need some help on finding a specific product for a specific use. Basically I'm looking for a brake caliper that would be very narrow on its right side (PM or IS mount) as I don't have a lot of space between the disc and the spokes. Regular two pots calipers are too thick (they're usually 16 or 17mm wide from the disc to their outer right edge), but I was told that some 4 pots (Hope brand?) are narrower due to smaller pistons. Also, I heard that Clarks Exo (?) are very thin but couldn't find any data on their actual size.

My plan B would be to use a second hand Magura Louise single piston as they are only 10mm on the side which is between the disc and the spoke. But going back to such an old tech is not exactly exciting...

Anyway, here is where it will be installed:
 

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Discussion Starter · #3 ·
I don't know anything about unicycles it looks like the caliper mount is on the opposite side of the disc in the pic?
You're right, sorry I didn't give all the info. This is still at prototype stage, and the frame that I'll be using for the final build has the caliper mount on the left leg.

This frame is meant to have an outboard disc, mounted on the right crank directly. But that cannot work with a geared hub.
 

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You might find a mechanical disc caliper that's thinner on the inside... They can approach hydro feel with a good cable and Jagwire or Yokozuna compressionless brake housing.
 

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Discussion Starter · #5 ·
You might find a mechanical disc caliper that's thinner on the inside... They can approach hydro feel with a good cable and Jagwire or Yokozuna compressionless brake housing.
Thanks that's an idea. I've never actually tried a mechanical disc! Are they that good? Any particular model I should look into?
 

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You might find a mechanical disc caliper that's thinner on the inside... They can approach hydro feel with a good cable and Jagwire or Yokozuna compressionless brake housing.
Thanks that's an idea. I've never actually tried a mechanical disc! Are they that good? Any particular model I should look into?
Maybe BB7 for road bikes, or other road caliper?

-F
 

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TRP Spyre SLC is impressive on my daughters CX bike.

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TRP may be too thick, the arm goes on both sides, taking up space

then again, it isn't that thick

https://images.immediate.co.uk/prod...019/03/1386017556068-4ahsd4k1xily-fa61cc4.jpg

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Avid BB is going to be ....

https://i.ytimg.com/vi/Ch0OlelgFaA/maxresdefault.jpg

apparently shimano xt hydros are the best at spoke clearance
https://forums.mtbr.com/brake-time/what-hydraulic-caliper-has-most-spoke-clearance-275286.html
 

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Discussion Starter · #9 ·
Did some research and indeed the TRP Spyre seems amazing, but it's got a two piston thing so it's probably too thick on the spoke side. Now if you have one at hand, would love some dimensions as that's been really hard to find any data!

Read that the Avid BB7 is rather bulky. Found an out of production Shimano CX77 which could fit neatly. Looks like they still make a slightly cheaper version of it, name I forget right now.

Don't know about the XT Hydros, would have to find one to be able to measure it. Magura made a Louise and a Clara which, apparently, were about 10mm thick on the spoke side - they only have one piston, on the outer side. Most 2 pistons are more in the 17mm region. I think I should be able to squeeze a 14mm caliper, max. It would be nice to fit dual pistons if possible.
 

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see post #3
I should of read all the posts before I hit reply.

I think I should be able to squeeze a 14mm caliper, max.
Is that the minimum clearances between the spokes and the rotor?

What's the clearance between the crank arm and the rotor?

How much clearance is there between the inside of the current IS mount and the rotor if you put the rotor on the other side?

What type of brake mounts are you looking at putting on the fork?

Have you looked at any flat mount road calipers?

Some of them look narrow but I don't know if they're any narrower than any post mount calipers or old IS mount calipers you've looked at.
 

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Discussion Starter · #13 ·
There is about 11mm between the spokes and the rotor, so not much. I can probably offset the disc by 3mm, bringing it very close to the left leg of the frame. That's still not enough for most rotors.
Today I went to a bike shop with quite some choice. We measured a lot of calipers. Shimano XT are the thinest, in the 15mm region. And they're round, so that could almost work. The guy said: "why don't you put the spokes inboard?". Well for me it was a no-no, but I started to google that and apparently it's possible. Yet I have to find a proper way to do it (the one link I found is dead), and I don't want to lace the wheel radial. But that would give me way more space!

If I put the caliper on the right leg of the frame, then the caliper would have to be upside down, no?
 

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Discussion Starter · #16 ·
Is going to a larger rotor an option? The further away from the axle/center of the hub, the more clearance you get with the spokes.
I've had to size up on a couple frames to get clearance and never regretted it.

Love the project!
Thanks!
Unfortunately, it's already a 203mm, so the biggest rotor available!
I'm now looking into alternative spoke pattern, have some hope down that route. Oh and I also found a second hand Magura Clara caliper which should fit. But now I want to go the extra mile and fit a more modern brake. Single piston sounds like not the best tech when it comes to brakes...
 

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I only rode a unicycle a bit way back in my college days and was never very proficient so am only theorizing on what might be good or bad. I would not think that a unicycle would allow braking to the degree and duration that can be done on a two wheeled bike. And I'd guess that on a unicycle, the most important attribute of a brake would be modulation, the ability to easily and naturally exercise fine control over the amount of braking. I posit that a powerful brake, one that generates a lot of braking force with little lever effort would be difficult to adequately control and provide braking in well excess of what could be used. Given that, a single sided mech caliper might possibly be a better choice than the usual mtb hydro brakes.
 

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Discussion Starter · #19 ·
You should try getting back on the wheel! I did the same actually. It's a pretty fun workout, and a nice community.
You're correct, the brake is more used to help when going down a slope or a hill (or a mountain but not with this one), so the force exerted on the wheel is not massive. But it's nice to have control, and power since you can only put one finger on the lever. But I think you're probably right, a single piston is probably enough. It just bothers my OCD to do all this work and settle on a 15 years old tech for the caliper!
 

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Discussion Starter · #20 ·
It happened! Finally!

Took ages because I was not crazy about using a Magura Louise or Clara since those are essentially bending the disc towards the non-piston side of the caliper. I sourced a Magura Gustav brake on eBay - those are still popular among downhill MTB riders and are surprisingly expensive for a 10 years piece of kit. The Gustav is also a caliper with a non-piston side like its contemporary friends but it has two pistons on the other side. And the whole caliper is mounted on what Magura calls a 'hanger' on which it can slide sideways. Basically it's a floating caliper, a technology used in cars and motorbikes for decades before opposite pistons became the norm.

I learnt about the details of this brake the hard way: the one I bought was surprisingly cheap... because it didn't have the hanger. It took ages to source the right one (Magura offered 11 different models at one point!) and at a reasonable cost. Special thanks to Magura USA (not DE...) for pointing me in the right direction.

Here is the hanger - photos are sideways. I had to grind it a bit as it was too close to the rotor. The rotor is very close to the fork, more than usual.

Circle Bicycle accessory Synthetic rubber


The caliper in place - again, fork is upside-down:

Metal Iron Steel Aluminium Plastic


And with the wheel in place. You can see how narrow it is on the spoke side of the rotor. The nice thing is I could go back and re-lace the wheel with the spokes in a more usual 3 way crossing. I guess it's still popular with downhill riders as it lets you build a stronger wheel with not much dishing unlike modern calipers - Magura also offered a Gustav hub back in the days:

Bicycle wheel rim Bicycle tire Rim Bicycle accessory Spoke


Ok, all in place now:

Bicycle tire Tire Wheel Bicycle wheel rim Spoke


And the whole beast:

Bicycle tire Tire Bicycle wheel rim Wheel Bicycle wheel


I still have to optimise the angle the caliper makes with the rotor with .2mm washers which should arrive by the end of the week. Magura's literature claims there will be a constant rub noise but no actual rub: "the wheel can spin 10 rotations without stopping". In my case, the angle is partly due to the frame not being super straight. I check the wheel in a truing stand, and it's perfectly aligned...

This build went on for ages but I'm happy I took that challenge. I've been wanting to put the Schlumpf in a 32" wheel - except there is no way to have rim brakes on those - so now I know I can do it. And in theory, the 32" wheel will fit just perfectly in this Mad4one frame...

Thanks again for Lobbybopster on the US Unicycle forum for sending me down the rabbit hole of Schlumpf disc brakes! It's been fun and a learning experience.
(ok now I have to go try the thing, but the weather hasn't cooperated lately)
 
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