Rhythmic noise when braking

Albi

Not a nice rhythm like some trance(?), but more of a clunk on each revolution.

As far as I can tell, it appears to occur where the brake pads come in to contact with a very tiny metal mark on the wheel rim. The mark is about 0.5mm in height, and 1.5mm in length. I've attached an image with the mark highlighted.

I am rather new to this biking malarky, so am not sure what this is. It doesn't look like rim failure pictures I've seen online, but is this the first step towards that? Can I just sand this mark down?

keef66

What wheels / rims?

Hard to tell from such a tiny photo, but that looks more like a small hole than something a brake block would catch on. If it's sticking out then by all means sand it off.

My Shimano wheels have wear indicators in the brake tracks; tiny dimples milled into the surface which when they disappear mean the rim's reached the end of it's life. More or less on the opposite side of the wheel from the valve hole. Can be hard to spot until you really clean the rims.

In my experience what you describe is most commonly caused by either:

1) imperfection in the rim joint
2) ding in the rim after a pothole incident

Albi

thanks for the reply,

they're bontrager race lite (clincher) wheels.
it's sticking out, rather than being a hole.

just had a look online, and it seems that most rims have a shallow groove all around the rim as a wear indicator. This is pretty much flat - I guess means the rims are worn?
Is it really bad to ride with worn rims?

does this mean I need new wheels?! if so, any tips on where to get wheels and how to choose them?

Albi

...although it seems that not all wheels have wear indicators.
The surface is very flat, so it's not bending out of shape at all. I might measure the rim thickness, and/or take it to a shop to check it out...

keef66

Many wheels have no wear indicators. You'd have noticed if they had the groove all the way round from new presumably?

If they aren't obviously concave they are probably OK

Albi

thanks for letting me know!
i picked it up second hand, so no idea if they should have had a wear indicator.
They aren't concave at all, so i guess they're ok for wear. No idea what the little bumps/marks are so gonna head to a bike shop and see if they know....

Albi

apparently, it's likely to have been caused by something like a stone in the pads. I can just use a mavic abrasive rim cleaner if i want to smoothen it, although it should happen just by using the brakes.