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Old 2019-04-16, 08:34 AM   #16
Eric aus Chemnitz
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So you have the rotor on the hub (inside the frame) but on the right side of you uni? So you brake points to the front?

The caliper must always be on the back side of the frame and on the right side of the d'brake. Therefore, internal (on the hub) disc brakes are always on the left side of the uni, external (on the crank) always on the right side.


I fear, that you run your brake backwards
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Old 2019-04-20, 03:51 PM   #17
SanJoseUnicyclist
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Eric, my apologies if I described the setup wrong. Your picture is exactly what I have set up. The disk is mounted internal to the frame. It is mounted on the left side. So, the D-bracket holds the calipers behind the disk (in back of the rider).
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Old 2019-04-23, 09:12 PM   #18
bristlecone
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I've used disc brakes on very long descents without noticing a problem. I haven't checked the temperature, because there was no problem and I assumed it would be too hot to touch. Hot is not a problem on its own; it's just friction. So my point here is that a disc brake should work for very long steep descents.

So if your brake is getting wobbly, there is probably something wrong with your setup, somehow.

My first suggestion is to ignore it. It's not a wise suggestion, but one that is wrong less than it is right.

I don't have a next suggestion. I can say that there should be no noise when you hold the wheel in the air and spin it, and the wheel should not slow and suddenly stop on its own after a few revolutions. If those things do happen, it might be because the brake pads are passively in contact with the rotor. Try loosening the bolts on the brake (not the bolts to the frame, but the bolts connecting the brake housing itself to the adaptor which connects to the frame), then pull and hold the brake lever, then re-tighten the bolts. This aligns the brake to the rotor. This can reduce or eliminate any rotor-brake pad contact when you are just riding. If this had been happening, fixing it could help with downhill performance problems.
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Old 2019-04-23, 10:08 PM   #19
finnspin
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Quote:
Originally Posted by bristlecone View Post
I've used disc brakes on very long descents without noticing a problem. I haven't checked the temperature, because there was no problem and I assumed it would be too hot to touch. Hot is not a problem on its own; it's just friction.
Sorry, that's just blatantly wrong. Excessive heat is a problem with brakes.

It causes:
- Brake fade from pads getting too hot
- boiling brake fluid, leading to spongy brakes
- Seals in the brake starting to leak quickly
- Brake disks overheating and changing their material properties leading to rust
- as mentioned in this thread: brake disks deforming. The material expands, and since it has nowhere to go radially, it will become wavy.

If you are not experiencing problems, it's because you are not going fast enough to get the brake to it's limit. It's simple physics: when you go down a hill at constant speed, you are converting potential energy from height into heat by using your brakes (and some rolling resistance, leg muscles and wind resistance.) The faster you go, the faster you produce heat, and the hotter your brake gets, since it can't transfer the heat to the atmosphere fast enough.

Quote:
So my point here is that a disc brake should work for very long steep descents.
"a disk brake". Look up some tests, and you will find that different models of brakes have very different capabilties, especially when it comes to when they start fading from heat.

Quote:
Originally Posted by bristlecone View Post
I don't have a next suggestion. I can say that there should be no noise when you hold the wheel in the air and spin it, and the wheel should not slow and suddenly stop on its own after a few revolutions. If those things do happen, it might be because the brake pads are passively in contact with the rotor. Try loosening the bolts on the brake (not the bolts to the frame, but the bolts connecting the brake housing itself to the adaptor which connects to the frame), then pull and hold the brake lever, then re-tighten the bolts. This aligns the brake to the rotor. This can reduce or eliminate any rotor-brake pad contact when you are just riding. If this had been happening, fixing it could help with downhill performance problems.
That could be a problem, and should definetely be done. But the problem of a disk getting wavy is a real one, and while readjusting the brake may reduce it, it will remain a problem.
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Old 2019-04-25, 03:58 AM   #20
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Thanks very much, Bristlecone and Finnspin! I appreciate your help.

I'll double check tomorrow, but I'm pretty sure that my disk is not warped and that my pads are not touching the disk when disengaged (maybe there is just a tiny bit of rub, but it’s imperceptible and it’s #$%&@ hard to adjust to the point that there is zero rubbing).

I think I’m going to simply take the muni to a quality mountain bike shop in San Jose and have them double check the setup and the durability/quality of the brake system that I have relative to better options that may be out there.

I've been starting to ride down more and more hills, and it's only this one really steep hill that gives me problems. But, it gives me problems every time and I'm starting to ride down this hill three times a week.
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Old 2019-04-27, 05:18 PM   #21
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OK, went to La Dolce Velo in San Jose. This bike shop has great reviews and the mt bike guy that helped me really new his stuff.

He suggested a 203-mm disk. I’m going to get the Shimano XT RT86L 6-Bolt Ice Tech Disk ($56 US). I really stressed how important it was for the break to be forgiving (can’t be jerky). He suggested the TRP Slate T4 Brake ($120 US). These brakes have 4 pistons rather than two, and the guy said that this was an important improvement given that I said control and not overheating were my two big needs. I’m a bit nervous because reviews online say the brake does not have as much braking power as more extreme downhill mt bike brakes. However, all reviews talk about how good the control is with these brakes: “The modulation is incredible, with a smooth and linear power curve that is highly predictable. If TRP could somehow retain the G-Spec Slate’s class-leading modulation while offering a little more ramp-up in power, I could see these going to the next level. As it stands though, these are a reliable and well-priced trail brake for those who value feel over outright stopping power.”

All my fingers are crossed on how well all this stuff will fit... It was all ordered online (but I just put a bit down)... I’m going to have the bike shop install the brake. So, I need to wait until mid-May to get them on the muni…

I’ll report back in!

Oh, one more question, the guy also suggested metal pads over ceramic. He said that the metal may be noisy, but will be better. Does anyone know how noisy metal pads are?

Last edited by SanJoseUnicyclist; 2019-04-27 at 05:26 PM.
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Old 2019-04-27, 06:16 PM   #22
JimT
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The larger 203mm disk makes sense because of the larger area to dissipate heat and the Ice Tech disks seem to have good reviews.
I changed my metallic/sintered pads for organic/resin to get much smoother and easier to modulate braking action. The organic will not last as long but are easier on the disk (less disk heat build up). They may fade more then other pads but for me I don't go down hills more then about 1/4 mile or so anyway.
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Old 2019-04-27, 07:54 PM   #23
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Some disk brakes squeel. I've had organic disk brake pads that did it, and metallic ones. It usually dissappears with either material after bedding them in for a while.

I don't think the reduced power they talk about in the reviews will be an issue for you. 1: it's probably stronger than your current one. 2: I found that the tire is the limiting factor in most conditions, not the brake. You can't brake more than your tire, and for unicycling, when you need the most braking power is for very steep sections. For Mountainbikers that slow down from 50 km/h, the limit may be the brake sometimes, as they have to use them to slow down quickly for turns.
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Old 2019-04-29, 06:35 AM   #24
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The brake will be fine. As said the 203mm rotor will take a lot of heat. One thing to consider is the D´brake adapter. Due to it´s construction it is by far not as stable as a welded brake mount. It tends to vibrate which you will recognize as noice (must not be, but likely, especially with the large rotor using another adapter for the brake-caliper). If you recognize this, it is most likely not your pads and you should consider this easy fix:

post #57:
http://www.unicyclist.com/forums/sho...+strebe&page=4
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Old 2019-04-29, 07:14 AM   #25
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From my experience, "noise" isn't the best description for what can happen with a flexing D-Brake. Massive vibration under my butt, and not in a pleasant way is what I had, before I made up a "Hugo strut" as kunstrasen linked to. But not everyone has that problem, it's highly dependant on your brakes, pad material, frame stiffness, riding technique etc.
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Old 2019-04-30, 02:58 PM   #26
SanJoseUnicyclist
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Does anyone know of a good torque requirement when tightening the bearing housing screws on the KH frame? On the KH website, the only guidance given is:

"... tighten the bolts with slight hand pressure. To test whether the bearing housing bolts are too tight, give the wheel a spin. The wheel should spin freely. If it does not turn perfectly freely, the bearing housings are too tight, and should be loosened slightly. Overly tight bearing housings will damage the bearings, and will not be covered by warranty."

Since I'm going to have a bike shop install the disk brake, I know that most of the mountain bike components provide torque requirements and the tech's are used to tightening screws to a required torque. Without a torque requirement, I could imagine the tech being ignorant about uni's and cranking on the screw to the point of damaging the bearing.

(I searched the forum, but could not find a discussion about torque requirements.)

Thank you!!
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Old 2019-04-30, 04:58 PM   #27
JimT
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Quote:
Originally Posted by SanJoseUnicyclist View Post
Does anyone know of a good torque requirement when tightening the bearing housing screws on the KH frame? On the KH website, the only guidance given is:

"... tighten the bolts with slight hand pressure. To test whether the bearing housing bolts are too tight, give the wheel a spin. The wheel should spin freely. If it does not turn perfectly freely, the bearing housings are too tight, and should be loosened slightly. Overly tight bearing housings will damage the bearings, and will not be covered by warranty."

Since I'm going to have a bike shop install the disk brake, I know that most of the mountain bike components provide torque requirements and the tech's are used to tightening screws to a required torque. Without a torque requirement, I could imagine the tech being ignorant about uni's and cranking on the screw to the point of damaging the bearing.

(I searched the forum, but could not find a discussion about torque requirements.)

Thank you!!
I think the spin free method is the best. Just direct anyone messing with it not to over tighten.
Unless you do like I did, then you can torque to the limit of the fastener.
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Old 2019-04-30, 04:59 PM   #28
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It's too little torque for most torque wrenches. So the KH instructions are the best guide there is. You should also make sure the D-Brake adapter is installed correctly. (Tighten the back bolt all the way down first, then snug up the front.)

With the amount of instruction you'll have to do for the uni specific parts, I'd just have them install the disk on the wheel, and shorten the lines, then do the rest myself.
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Old 2019-08-01, 04:17 AM   #29
SanJoseUnicyclist
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Ok, I finally have my new brake and have put a couple hundred miles on it.

Here is what I purchased:
- 4-Piston Caliper: TRP Slate T4 Four Piston Caliper (front) for $120 US
- 203-mm Rotor: SHIMANO XT SM-RT86 6 BOLT ICE-TECH ROTOR for $57 US
- Metal brake pads with cooling fins: Shimano H03C Metal Brake Pads with Cooling Fins for $30 US

Total was $210 + tax and $60 for install.

Am I happy? Yes and no. First, I figured that with 1) a 203-mm rotor, 2) a four-piston downhill mountain bike caliper, and 3) metal brake pads, that I’d notice a huge difference in braking power (by this I mean less force on the brake lever with my finger for more braking force). However, the braking power of this relatively expensive setup is very similar to my original Shimano BL-M445/7L Disc Brake from Unicycle.Com. As a matter of fact, after this first-hand comparison I’d highly recommend the Shimano BL-M445/7L Disc Brake from UDC for most riders.

The big difference is that my TRP/Shimano-Ice setup does not overheat at all. I have ridden these steep/rocky hills (>20% grades) 3 to 5 times per ride about 3 times a week with no overheating issues.

But, there is one huge caveat! The brake chatter that Kunstrasen and others mentioned is very real with the 203-mm rotor. If I had to do it all over, I’d stick with the smaller rotor. The brake chatter that I experienced with the 203-mm rotor was severe and I could not ride a couple of feet down the steep grades without being tossed. The only solution was to use Kunstrasen’s support bracket design. THANK YOU for the design tip!!!!!!!! I’d be out of luck without that bracket.

My big takeaways:
1) Don’t get a 203-mm rotor

2) The TRP Slate T4 has incredible modulation. So good that I can switch hands during the steepest parts of these declines. I feel modulation is extremely important for muni.

3) Don’t hesitate to get metal brake pads. I don’t think they are overly aggressive! I’m amazed that I can’t tell the difference between the original Unicycle.com brakes and these expensive brakes (other than the fact that the expensive brakes do not over heat!).
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Old 2019-08-01, 09:57 AM   #30
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Good to hear the overheating is solved!

Quote:
Originally Posted by SanJoseUnicyclist View Post

But, there is one huge caveat! The brake chatter that Kunstrasen and others mentioned is very real with the 203-mm rotor. If I had to do it all over, I’d stick with the smaller rotor. The brake chatter that I experienced with the 203-mm rotor was severe and I could not ride a couple of feet down the steep grades without being tossed. The only solution was to use Kunstrasen’s support bracket design. THANK YOU for the design tip!!!!!!!! I’d be out of luck without that bracket.
As I mentioned, I had that brake chatter with a 180mm rotor, so I'm not sure it depends on brake disk size alone, but probably more on pad compound, frame stiffness etc. The support bracket will also help the Adapter not break (which they sometimes do), so it's definetely worth it for anyone.

I'm in the market for a good 4 piston brake (well, that's when I have some money to spend), so I can add the slate t4 to the list of candidates now. How far away from the seat does the brake lever end up?
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