Machined brake surface on rims

I’ve read in a number of threads about the need to have a bare metal surface on the rim for the brake pads to rub against. It’s pretty obvious in theory why this would be. However, I just noticed for the first time, kind of by accident, that my Nimbus 26" with Magura brakes has a completely black wheel, with no machined brake surface. I’ve been riding this for the better part of a year now (I bought it used from another forum member), and never noticed it until today. I looked pretty close, and there are no indications of the brake area being scratched, bunged up, or messed with at all. It’s just black all over. (Presumably powdercoated.)
So my question is, what are other people’s actual experience (not theory)? If you have ridden on powdercoated rims with no machined brake surface, what has happened?
I’m wondering this because I’m shortly going to be building up a new uni using the Kent 32" wheel, which happens to be black (looks like regular paint), that has no machined brake surface. I’m planning on changing the color (stripping and powdercoating), and I’m planning on running Magura rim brakes, so I’m wondering if I really need to keep the sides of the rim bare metal. I would prefer to powdercoat the whole thing without masking or post-process machining. Particularly since unicycle brakes are not typically as critical as on a regular bicycle. (I find it convenient to slow long downhill descents and when coming up to a quick stop, but a lot of folks never use them at all.)
Thanks for your comments.

I imagine the paint will wear off pretty promptly, and then you’ll have your bare aluminum sidewall anyway. The important thing is probably that the rim shape has straight vertical sides that make good braking surfaces.

“Machined” isn’t the same thing as bare aluminum, by the way - somewhere along the line rim manufacturers started machining the raw rim sidewall to make it flatter and remove any side-to-side irregularities, which gave modestly better braking at the cost of rim life (because the rim material is removed unevenly, making for thin spots). Curmudgeonly riders like me, who wore through rims all the time, preferred the old unmachined rims.

If your rims are in fact powder coated you will notice a great improvement once the powder is worn off. My guess is that it is black anodized, which is essentially a dyed rim. Anodized rims work with brake pads just as well as machined rims with the exception of “hard anodized/Ceramic” rims.

Machining sidewalls was started due to the fact that hard anodizing became popular, but the braking quality suffered. They came up with all sorts of different rubber compounds to try to correct the problem, but in the end taking the anodizing off of the sidewall was the real solution.

I have powder coated rims on my tandem, and only now after a few hundred miles is the powder wearing off enough to quiet the braking a bit. We nick named the bike “the Honking Goose” due to the sound it makes when braking.

I’ve ridden both. My anodized rims seem to do worse when wet then the machined ones do when wet, but the difference is mostly negligible.

My next rim is going to be fully powder coated for asthetic since I’ll be running a disc brake.

Vee brakes combined with the powder coated rims on my coker we’re not usable, IMO - no matter how I adjusted the pads the action was on/off. I’d bet it would have worked better if I had sanded the powder coating off, but I went disc instead. It was the right choice for me.


I had painted (powder coated) sidewalls on my first 36er rim. I was getting that awful wwwwwWWWWWWWWWWWAAAAAAAaaaaaaaa noise after a while and it didn’t take me very long before I sanded clean the braking surfaces. It wasn’t all that bad with the painted brake surface but braking performance increased in almost every way with the bare aluminum braking surface.

Quieter, more consistant, less affected by moisture, and better modulation.

Thanks for the input, everybody. I’m building the wheel (a 32") with a Schlumpf hub, and although people have successfully run discs with Schlumpfs, it seems like rim brakes are a safer bet, so I’m inclined to use them. My 26 and 36 have Maguras, and I like them, so I’ll probably go with them again on this one. This will be strictly a road uni, so the brake will get light use (judging from the use it gets on my 36").
Based on the above experiences, I think I’ll just go ahead and powdercoat the whole wheel, and if I don’t like how the brake works later, just sand the braking surface.
Interestingly, there is an inscribed groove on the Kent 32" rim, inset from the edge by about .30", that looks like it would make a good line of demarcation between the bare and painted surfaces.

udc titan on US site had option of u-brake
but the rim doesnt have a machined surface :thinking:

My s2 rim has a machined surface.

okay! i guess the picture on the website isn’t accurate :slight_smile:

I went and looked at it, that’s weird. Maybe they make a special rim version for the titan. Killian, or someone else with a titan, could you shed some light on this?

My S2 doesn’t have the machined surface. Nurse Ben’s does. Of course, Nurse Ben’s isn’t on a titan. Perhaps they did that to keep cost down. :thinking:

I have no idea why they are different… After 6 months of riding though, the anodizing is starting wo wear off though.