Nimbus 36 Oracle frame

Overall I’m very happy with my new frame. Mine came from UDC-US without the stickers on it (they came separately in a baggie), which is great. Nice clean black paint (I would have removed the stickers anyhow, and now I have them to stick on mugs and whatnot). The braze-ons for leading the disc brake line are a really nice feature. And the frame came with a new double quick release clamp (review in separate thread).

However, I do have one gripe. After installing the brake’s disc, and using the bearing spacers supplied with the hub, the screws for the disc rubbed against the weld on the frame. My options were to return the frame [PITA], pull the bearing and grind the screws [PITA + risk of having the screw heads break off], or grind the frame. I decided to grind the frame, because it was least inconvenient, and very little material needed to be removed so it was less risky than grinding the screws. It only took about the width of the paint + 1/2mm, and now I have clearance that a piece of paper will barely slide through. Screws were as supplied by Magura with a new MT2 brake and Magura Storm rotor.

This wasn’t a huge deal, but I would have had to return the frame if I didn’t have a dremel, and now I’ve probably voided my warranty just to make the thing rideable. Seems to me the clearance tolerances need to be a little bit larger.

Picture of frame after screws rubbed, and before I otherwise did any grinding:

Are you going to touch up the paint, or just leave it? Sounds like you’d have to take more metal off in order to touch it up.

I’m just going to leave it bare aluminum - you can’t see it without a very close inspection, because it’s on the inside of the frame right up against the disc brake.

Also, I should have noted that I’m using a Nimbus Oregon hub, in a wheel built by Josh at UDC-US.

It’s not like it’s going to rust! :wink:

I suppose the aluminum could oxidize given enough time and moisture :roll_eyes: , but I was thinking more of whether the surrounding paint might flake or peel off. I bet the quality of the paint is such that it won’t do that either. Besides, grinding off metal so you can add paint, even when it is so little metal, seems kind of silly.

That is pretty damn tight to have that happen :astonished: does it look like it is just due to bigger welds than normal?

On my Triton / Spirit setup I have got some countersunk bolts coming and will countersink the rotor holes accordingly to help avoid any possible issues, for the cost of £1.99 for the bolts it seems a no brainer,

The welds look normal, nice and smooth, and about the same on both legs. The welds do protrude from the tubing a little, but I consider that to be normal. My grinding only took off a little of the weld material.

I’d be nervous about trying to countersink the holes on the rotor - not much material there.

I intend to abuse the uni enough that it will lose more paint in other places from UPD’s in any case. :slight_smile:

Countersinking the bolts on the rotor is actually a good solution… The main problem is with the clearance on the KH cranks and their frames. If you countersink the disc you can use countersink M5x10 bolts. This changes the bolt height from 3.5mm to 1.5mm. This means that you don’t need to file the frame down to make them fit. It is also in engineering terms a good solution.


Roger, are you indicating that these frames will typically rub against standard disc bolts?

No, this is the first time I have heard of a oracle with this problem.

Granted, using a disc brake on a unicycle, with the cranks and caliper having to exist in the same place, there is not much wiggle room. Even on my Steel Impulse frame the 200mm rotor is only a couple millimaters from the frame.

James, can you tell whether it’s just an “off frame” or is it possible the 2mm spacer was left out; this is the spacer that goes between the disc side bearing and the disc side hub flange?

Some bolts are thicker, but not enough to make or break frame clearance.

A thicker spacer between the bearing and flange would be the easiest, and the frame will flex fine, might have to recenter the rim…

OK, thanks. It’s probably just a slightly over-thick weld. Anyhow, it was a quick and easy fix, didn’t remove enough material to be concerned about strength, and I’m loving the uni.

The frame appears to be even, although I have not taken calipers to it to measure the welds. Yes, I did install the spacers. Anyhow, it’s fixed now, point of the thread was to post my overall positive review, but objectively, so I noted the issue. Honestly, without this thread I probably would have forgotten about it by now. I also have no doubt that UDC would have replaced the frame if I had asked.