Magura rim brake fit issue on QU-AX

So, I just got all the pieces to put a Magura HS11 rim brake on my aluminum QU-AX 27.5" unicycle frame which has a 27.5" rim, the only problem is that the brake doesn’t get close enough to the rim no matter how I adjust the fit of the rim brakes in the mounting assembly. I thought perhaps I could get a wider rim for that, but the other perhaps more unsettling part is that even if I could get the rim brake close enough to actually contact the rim, it seems like the brake shoe would only contact about 3/4 of the rim; the brake shoe is too close towards the hub. It is almost as though I would need a 26" rim or so. It doesn’t make sense to me, this unicycle has the mounts for the Magura brake, and it is billed as for a 27.5" rim. When you look at the picture without the rim brakes on the centre of the magura braze-on mounts is not in the centre of the rim - was my unicycle made with the mounts in the wrong place? Has anyone else run into this before? Any ideas of what I could do besides putting on a smaller diameter rim?

That looks like a 26" frame.

26" is these days a BSD of 559mm, with 27.5" being 584mm

I dare say that 12.5mm difference would put the rim in the correct place for those brake mounts.

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Also the very limited clearance between the top of the tire and the frame could indicate a 26" frame. It looks like a regular width tire (2.3"?) and not a particular large tire.
I have one of those frame in 24" and it fits plus size tires and with a regular tire there is quite a lot of clearance between the top of the tire and the frame.

I’m only aware of special magura mounts that can change the distance between the rim and tire needed if you have a very narrow or wide rim. I’m not aware of any that can chance the up/down positioning.

I also suspect that it is a 26" fork, because the inner height of the QX26 fork was very generous, so that with a 3" tire there was still room for an SKS mudguard. Therefore, your 27.5" tire will also fit in well

I guess an easy solution would be to make a pair of adapters which would move the caliper up a bit.
I had a similar situation (the rim was too far from the pads) and made a pair of adapters:

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Thank you. I have begun to wonder that I may have gotten a 26" frame afterall. The reason I thought I had a 27.5" frame was that the company I bought it off gave me a great discount when I tried to buy a 27.5" steel framed QU-AX uni and they had none in stock anymore. I think the shop owner was confused about what size it was as it also was on display. So, I just took him at his word that it was a 27.5" uni. So, I’ll probably disassemble my 27.5 wheel and use a wider 26" rim I have in the garage and rebuild the original wheel I had made for this uni, also get a wider tire.

Thanks again.

You are correct, this tire is about a 2.25" Hans Dampf tire. I think the shop owner - of a circus company just didn’t know his sizes when he sold me this uni frame that was on display. It seems that this really is a 26" frame, so I should build a wheel based on a 26" rim. Thanks.


Thanks, I think you are right (and a number of others have thought this also), that I actually have a 26" frame. I am disappointed because I believed that it was a 27.5" frame, and I had originally build a 26" wheel because that was the only rim I had available at the time, then when I got my hands on a 27.5" rim I took that one apart to build the 27.5". Ok, wheel building time again. I am glad that I could get a wider tire on, like about 3". I am hoping to get into Muni a bit more … I am still very much more a commuter at this point. Maybe the brakes and a wider tire will help encourage me to skill up to be able to handle rougher trails and manage drops better. Thanks, Dawson

I guess the 27.5 size became mainstream when disc brakes ruled vs 26" that is older and rim brakes were standard.

Thanks, I think that I have the 26" frame even though the frame works fine with a 27.5" rim, but to add the rim brake requires going back to the 26" rim. Wheel building time again.


I’m not even sure if a rim brake version of these frames existed in 27.5". As I built my G27.5er years ago and wanted a QX-frame with magura mounts for the Hugo-strut, I had to take a 29" frame as all 27.5" QX-frames only had disc tabs on.

There was a 27.5" version with a Magura mount

Yes, that is what I thought I had. I am now almost sure that I have the 26" one.

Quick update: I disassembled my 27.5" wheel, and built another wheel with a 26" x 38mm steel rim (sigh, heavier, but really solid), so this is a wider rim than the 27.5er … that should deal with the rim width issue I mentioned earlier. So, now I just have to true the wheel, make sure it isn’t dishing, or out of round. It’s not out of round now, and I don’t believe it dishes, but I haven’t had time to check that. I did a quick check to see if the magura brakes would cover the surface of the rim … shouldn’t be a problem. But, wow, that rim looks so small in the frame.

Thanks everyone for your help and suggestions.

I’ll post again after I assemble the brake and shorten the brake cable.

Should look more proportional with a big meaty tire in there, but maybe it’s just a big frame.

yes, it worked great with a 27.5" tire in there, and I figured I could even get a road bike width 29" in there, but the thing is I want to use the rim brake, so I think I’ll be looking for a 3" tire or around that, and it should fill things in nicely, and give me a reasonable diameter wheel to work with.

FWIW, here is what my unicycle looks like after truing the wheel I built, putting it all back together again, and installing the brake and handle and shortening the brake hose (it was about 2m long to start with). Yet to do is remount the brake handle so that the brake hose goes to the other side of the saddle post, tie it down a bit with a ziptie.

Then, learn how to ride better holding the saddle, and using the brake. An obvious upgrade is to find a beefier tire as well, but it is what I had in 26" size in the garage.

Here are the pictures:

And, thanks again to everyone who chimed in. Thanks to my son who gave me the idea to check with you all, and also gave me a hand with putting the brake together and holding things after I cut the brake hose to shorten it.

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Try rotating the saddle 360 degrees. Then your line is better managed

Ok, thanks for the tip that is a great idea. Never thought about that. I left a bit of slack because I wanted to ensure I could raise the seat a bit more depending upon crank length and if other taller riders wanted to use it.