What size discs for brakes?

My daughter, 9, and I have been doing a lot of unicycling lately. I had an old 24" Miyata unicycle in the garage and she found it and wanted to learn to ride. Given the lack of activities for kids during the pandemic she put a lot of effort into it and has become quite good. I told her that if she learned how to ride I’d get one myself and ride along with her, so I ordered a Nimbus Nightfox and then proceeded to blow out my knee before it arrived. While I was recovering I bought her a new 24" muni for her 9th birthday and then handlebars for Christmas, (which she said was the best present ever).

So the way things stand right now, I’m struggling to learn to ride a 36er and am up to riding about 1 1/4 miles a day. Muscle fatigue in my legs and lower back stops me after that. I used to ride a lot back when I was a kid, but the combination of that 36" wheel and 52 y.o. body made it a lot harder to pick up than I had anticipated. I remembered riding 5 miles at a time and hopping up curbs as a teen and just assumed I’d hop right back on. 36ers are challenging and fat old men don’t bounce back when they fall.

My daughter on the other hand can ride ten miles at a time and has no problem on the easier mountain bike trails. We go out for my unicycle ride, then come back and I switch to a bike and we ride another 4 miles or so.

So back to the original topic, I’m looking at getting brakes for her unicycle in the near future and for mine sometime down the road. She’s 9, about 4’2" tall and 60 lbs, (127 cm, 27 kg). I’m thinking a 150mm disc is probably about right for her, but I really have no experience regarding brakes on unicycles. I’m thinking the smaller disc should weigh less and give less braking force making it easier for her to master.

For me, I’m 6’1", 250 lbs, (185 cm, 114 kg), and I’m thinking a 180 or 203 mm disc would be better.

I’ve had good luck with Shimano Deore hydraulic brakes on bikes and figured I’d use them on the unicycles as well.

Thanks for reading my long first post and any advice you can give me. I’ll probably be ordering brakes in the next month for her and I might just get mine at the same time, although I don’t think I’m really ready for them yet.

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For you 180mm or 203mm disk may be best. With some frames (the QX rgb for example) it’s not recommended to use 203mm disks, as they can put a lot of forces on the frame. Really depends on your terrain if you need the extra heat capacity of a larger disk.
For her, 160mm disk will probably be good - but I don’t see much disadvantage to going slightly overkill.
Deore brakes are great, I run a xt 2 caliper brake and 180mm rotor on my Muni, and it works well. (I’m a lightweight at just over 60 kg though)

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My thoughts are she probably doesn’t need a brake on her 24 I or for that matter a handle bar. If she moves up to a 29 or larger wheel and is doing a lot of hills of down hill muni then go for a brake and handle bar.
As for you my friend and your pains and stamina issues, this is coming from another 52 year old rider. Cross Train, practice riding as much as you can, exercise your core and drop some weight if you can. you will be riding longer distances than you ever though possible. Take this winter to prepare for spring riding. I always stretch before a ride, a little ibuprofen definItely helps, try taking some before you ride.

Well, I can only share my own limited experience on unicycles, but I have quite some experience with brakes on bikes.
I can tell you what my setup is (I weigh around 200lbs): Shimano Zee 4 piston brakes on a 180mm rotor and a 27.5" wheel.
As the torque drastically increases with the wheelsize, you will need more power to slow down a bigger wheel than to slow down a smaller wheel.
What I understood from other riders is that you don’t need to be able to block the whole wheel with your brake, but I prefer to have that power, hence the 4 piston brake (deore won’t cut it).
Since you weigh already a bit heavier than me, and @finnspin states that 203mm might not be the best choice, I would recommend going for a 4-piston brake on 180mm since it’s the best you can do and a 36-er with a heavier rider definitely requires some serious stopping power.
Of course if you have long cranks you could use your legs as well, but the idea behind the 36-er is to make speed (shorter cranks) right?
Then you definitely need a reliable brake :wink:

The 4-piston XT brake should be sufficient as well, and if you can find it second-handed, $40 might be a good price already (I bought a set for 50 euro a few months back).

Your daughter sounds pretty amazing :slight_smile:
I don’t think discs come in 150mm size, or if they do, its very uncommon. I’d go 160mm which is a standard size.

As for you, maybe also get a smaller (midsize) uni. Your daughter will never keep up at the same speed (and her legs are too short), and a 36er is not suitable for technical trails really.

I always found a 36er too hard to mount, and not so maneuverable. Good if you are trying to go somewhere with bike riders though.

Splitting hairs about the brake rotor size.

Skip it on her 24" and order one on her 29" where she needs it.
She won’t be staying on that 24" for very long either.

When she starts borrowing your 36", then order your new 36" with a disc brake. :wink:

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Keep in mind that stopping g a unicycle and stopping a bicycle are two completely different actions. Brakes on a unicycle are for down hill control and sudden stopping to navigate an obstacle. I have bmx brakes on my 29 and 32 wheels and have them adjusted so a can ride through as I’m pulling on them. This is to keep control and save my knees on a down hill, I have no need for sudden stops… I Have a shamano discs on my 26 muni, I have had a lot of trouble getting used to the super sensitive nature of the disc and question my decision on installing it on my 26.

As for the riding advise have in my previous posy, that was a reflection on what I did to improve my riding. I was not trying to be a know it all and tell you what you need to do. When I started riding again three years ago I was 225 pounds, over weight and out of breath. I dropped down to 185 through unicycling exercising and dietary improvement. After a few rounds of broken toes early in the spring i put back on 15 pounds. At 200 lbs my stamina was greatly affected and I was having trouble free mounting my 29er. I have dropped that weight and my riding and mounting has improved.

Maybe there’s a difference between you and me. I come from a street trial and mountainbike background where I’m used to one-finger brakes to either feather for things like nose manuals and full stops for things like back hops and up to backs.
Therefore I have absolutely no issue using a very strong brake on my muni, although I’ve only been riding a unicycle for 32 days now…
And I already found some uses for it, which are a lot harder if you cannot block the wheel with your brake (try hopping your uni in any other foot position than level, especially if you are forward on a slope.)

But if you want more modulation, take a look at the Magura brakes. Especially the MT7 is famous in the street trial world for it’s strong stopping power and excellent modulation. It makes some sensitive moves so much easier than with other brands.

I have a brake on my KH24, and I use it on downhills. It’s not completely useless.


I definitely say there is a difference in our riding styles.based on what you just mentioned. The beauty of unicycling is there are so many styles of riding and our experiences are all
Different. The long and short of it is we have to find out what techniques and equipment work for each of us individualy. We get there by trial and error and seeking the advise if other riders

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Thanks for all the replies. The main reason for the handlebars on my daughter’s uni was that she was so jealous of the ones on mine. She really, really wanted handlebars, so for Christmas I gave her some.

Currently she has no problem keeping up with me. A 24" wheel with a 3" tire is actually really big for someone who is 4’2" so I don’t think she’ll be moving up to a bigger one for awhile. I actually had to cut down the frame about 3" and cut a new slot for the seat post clamp in order to make it fit her. She rides down some steep terrain on it and I think she probably could benefit from a brake. I know she had trouble controlling her descent on one particularly long and steep hill.

I’m currently using 170mm cranks on mine, but intend on switching to 150mm once I get better. What I’ve been doing is trying to ride every day and adding a little extra distance and difficulty to my ride every week or so. I’ve kind of figured out now that I’ll probably have to switch to a smaller unicycle for muni, but I’m going to wait until I get good with the one I’ve got now and get my back muscles in shape before I start buying a stable of them.

Share a video of you two riding!! :slight_smile:
I want to see it!

Also, my legs are on the shorter side too. On a 36er my legs only just managed with 150mm cranks. I found 125mm cranks good to ride with. Didn’t do any rough terrain with it though.

I think, you’ll find a 27.5" muni fun. I do :slight_smile:

I’ll try to get some video up tonight.

Curious if duff is short for something. My last name is Duffus.

No deeper meaning. I used the screen name Elmer Fudd for the longest time because I liked to hunt rabbits. These days Elmer Fudd is usually not available, so I just reversed it. Also, I like the Simpsons reference to Duff Beer.

Video of my daughter descending a hill about three months ago. This is on her old unicycle. She’s gotten considerably better since.


To use brake on downhill means to improve your skills and use a new way to keep front/back balance.
As soon she learn to use the brake as she will trust this new techniques.
She will ride faster and safer.

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Wow impressive I can see the brake helping her. Honestly I wasn’t expecting her to be doing that kind of riding. Best of luck to both of you., It looks like you’ll have loads of fun riding together.

Welcome here!
It’s impressive that your daughter can ride with those crazy long cranks! You said you used to ride back in the days, well if there is one thing that has changed is the relation to crank length. Your daughter would have more control with 137 or 125 cranks, and would probably enjoy even more - and yes that’s where the brake comes in handy.
I’d say same for you. If you’re exhausted after one mile, you must be too tense. And spinning huge 170mm cranks doesn’t help with the legs doing so much movement. Why don’t you switch to 150 asap, as it might be the thing that makes you better!

Very good! I think handlebars will help her too. And that wheel looks massive on her! Like me on my 36er :slight_smile:

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