Disk Brake mount questions

Few questions real quick.

I’ve used both the Nimbus D-brake as well as frame mounted tab’s in the past. All on the right side of the frame (I.E. external disk).

With the Nimbus, you are using the D-brake technically ‘backwards’ and clearance can be tightish with a Spyre. However, with rotor shims it’s fairly simple to set up.

With a frame mounted tab, I’ve found clearances to be far tighter however, and have had to Loctite the crank bolt since I’ve been unable to fully engage the crank on the ISIS interface.

For my next build, I’m torn between using an adapter or actual frame mounted tab. Which is where my questions come in…

For those using an INTERNAL rotor with a disk specific hub, is the tab spacing identical to that on a bicycle fork?

I’m aware that these hubs come without the disk side bearing mounted. Do these still need to be driven on like regular hub bearings (hammer and a pipe) or will they more or less slide/push on by hand?

Now if I decide to use an adapter, I’m seriously considering the Mountain Uni UCM. But I have a couple questions about that…

Is the UCM steel or aluminum?

It is designed to be used on either side so I think clearance would actually be even better than with the D-brake.

The Mountain Uni site says that they require a Shimano 180 ‘standoff mount’. (seen here: http://mountainuni.com/products/shimano-180mm-standoff-mount)

Is this really required or can I use the adapters provided with my TRP Spyre calipers?

Also, I use 160 mm rotors. This adapter is for 180 mm but Mountain Uni claims it will also work with 160. Can anyone confirm this?

Thanks all!

IS-to-PM adapter

I can’t say too much about the other stuff, as I’ve only used the D’Brake (both external and internal).

However, to me the “Shimano 180mm Standoff mount” looks like a standard IS-to-PM adapter (International Standard to Post Mount). They make these in all kinds of sizes so you just have to get the right one. You do have to be careful as they are different for front rear (a 180 front is a 160 rear) and these days the IS-PM is more common on the rear of a bike (this is detailed in another thread somewhere).

If this is right, then you just buy the appropriate adapter for 160mm rotors (don’t know it, but the yours for the “TRP Spyre calipers” is likely the same, as almost all calipers take post mount). Also for lateral brake placement to match the rotor, you should be able to shim or grind the IS-to-PM mount a little bit (shim should be up to 5-6mm, grind probably only 1-2mm).


On their website is says:

so aluminum.

Missed the whole 6061 thing on the website. Thanks for pointing that out.

Figured as much on the IS-PM adapter but wanted to be sure.


You’re probably aware of this already but the other difference between the UCM and D’Brake is how they mount. The UCM floats on both bearing cap bolts while the D’Brake is tightened hard against the rear bolt ear. You can see how the D’Brake is offset to allow for this in the pictures in this thread.

I’m not sure whether it makes a difference in practice, but the UCM might be slightly less forgiving of poor setup when it comes to vibration.

I’ve used the UCM and d’Brake (both external)

They both work almost exactly the same. I started a thread on it quite a while back. Post # 14 might be of interest to you.

I now use UCM with Schlumpf, and d’Brake on the other unicycles. They both work great.

EDIT: I forgot about the adaptor thing. The UCM uses front spacing so if you want to use a 180 disk you need the 180 front or 160 rear adaptor, for a 160mm disk you would need the 160 front adaptor. I believe it’s the same with the d’Brake but I would have to double check.

Eric, thanks for the link. I’ve seen the thread but missed that post. Very much what I was looking for (I think).

FWIW, with D’brakes I’ve always just used the 160mm adapter supplied with my brake caliper/rotor. I only asked the question because MountainUNI specifically sells a Shimano 180mm adapter. Sounds like it’s a non-issue to keep doing what I’ve been doing.

Gonna let this marinate for a bit… Need to figure out what’s going to be easier.

160mm front adapter is quite rare I think, so I would expect that the 160mm adapters you got with brake is actually 160mm rear adapter which is exactly same as 180mm front adapter provided by MountainUNI.

My setup is d’brake with 160mm IS-PM front Adapter for 160mm rotor.