Strange rim problem

[geomannie]

Hi Folks,

I have a strange but thankfully not too serious problem with the front rim of my bike. The rear rim while notionally the same model apart from being asymmetric, is fine.

The front rim is a silver Kinlin XC-279 and the problem is that is keeps picking up fragments of metal that weld themselves to the braking surface. The metal fragments are small, <1mm long & perhaps 0.5mm high.

The problem is that on braking you get a very irritating constant ticking (especially if more than one present) as the fragments pass under the brake block. The fragments do not appear to be bits of rim surface & I think are picked up from the road. The rim can "develop" several small metal adhesions in the course of a day's riding, especially if wet. The adhesions can be removed by scraping with a blade but they are well attached.

I am puzzled as to what is going on as this has never happened to me before on any other rim, and I have had many. And why the front rim only? Questions, questions.

The Forums hive mind appreciated. Here is a picture of the latest.

[geocycle]

Have you checked the brake blocks? I once had a batch of shimano blocks that collected shards and scratched the rim. Swapped to something softer and all was well.

[geomannie]

Yes, I have tried various brake blocks.

[axel_knutt]

I think you'll find that there are small pieces of grit getting on the brake blocks which scrape the surface of the rim, then the swarf either gets embedded in the blocks too, or stuck to the rim. I've had odd occasions when mine suddenly starts doing it for no apparent reason, then stops again a while later. There isn't much you can do other than keep up with the chore of picking the debris out of the brake blocks until they decide to stop doing it.

[PT1029]

The lumps on the rim are probably bits of grit embedded in the pad acting as a chisel on the rim. In general though, at work I see the lumps embedded in the pads - occasionally quite big ones.
The lumps on the rim can be filed off/flat. Even if the filed finish isn't perfect, it will be a lot better than the lump, and soon wear smooth.

Agree on trying different types of pads. Also worth trying to regularly clean the rim and pads.