Wheel noise on downhill braking

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yinya
Posts: 158
Joined: Tue Aug 07, 2007 9:06 pm

by yinya

I had at the same time the bearings and the rim replaced in my rear wheel (dt240, cx ray, boyd altamont lite). But now under heavy downhill braking there is a “tk-tk-tk-tk” noise. The wheel itself feels smooth and fine - meaning I cannot feel it physically. Just noise.

Any ideas what could cause it and what I could ask the mechanic to double check?


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by Weenie


mattr
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Joined: Fri May 25, 2007 6:43 pm
Location: The Grim North.

by mattr

Rim join? Can only hear it when you are braking hard, braking gently doesn't open up a gap.

yinya
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Joined: Tue Aug 07, 2007 9:06 pm

by yinya

Thanks! Any tips on how to test?


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mattr
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Location: The Grim North.

by mattr

Visually.

alcatraz
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Joined: Mon Aug 29, 2016 11:19 am

by alcatraz

pad alignment?

pad/chainstay clearance?

debris in the pads/tire?

wheel out of true?

yinya
Posts: 158
Joined: Tue Aug 07, 2007 9:06 pm

by yinya

Pads are good and aligned. Wheel is very slightly out of true (visually detectable, again cannot feel it when riding), so whatever the cause is, could be amplified by that out of trueness.


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alcatraz
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by alcatraz

The caliper follows the wheel when braking. So it's moving left and right with the rim. It's supposed to do that a little bit by design but if the arms are gritty around the center axle it could be stiff and fight against the rim. Just because it looks clean doesn't mean it's nice and free moving around all of it's joints.

If the out of true spot it sharp enough, maybe it can cause the caliper to produce a noise when it swings back and forth.

If it isn't a spot but more a larger area, you'd have to ride quite fast to get the caliper to make a noise.

I know it doesn't feel safe but as long as you're careful you can place your hand on the caliper when braking and feel the vibration. Maybe it will give you an idea what direction the caliper is moving when you hear the noise.

Also the frequency is useful. If it's once per revolution and always in the same spot. You can try to see the valve and use it as a reference. If you hear the noise and see the valve near the road at the bottom you know the noise is coming from the opposite side somewhere, and so on.

/a

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Calnago
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by Calnago

mattr wrote:Rim join? Can only hear it when you are braking hard, braking gently doesn't open up a gap.
^This. Can you run your fingernail along the brake track at the rim seam and feel a tiny ridge? If so, that’s the likely source of the “tick”. If not then look elsewhere along the edge of the rim for nicks etc that the upper edge of the brake block might be passing over each revolution. Or even the lower edge of the brake track for the same, although it’s more likely at the top where your rim edge may have come into contact with something. Or conversely, perhaps there’s something embedded in your brake pad that is not really noticeable until it ticks across the rim seam.
An out of true rim by itself won’t be the cause of an audible tick, but it could mean that you have zero brake modulation, since the brakes will “grab”’the highspot each revolution rendering modulation a big fat zero. Grabby braking is the polar opposite of smooth modulation.
Colnago C64 - The Naked Build; Colnago C60 - PR99; Trek Koppenberg - Where Emonda and Domane Meet;
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Nejmann
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by Nejmann

QR can make weird noises too.

TheKaiser
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by TheKaiser

mattr wrote:
Fri Jan 25, 2019 3:55 pm
Rim join? Can only hear it when you are braking hard, braking gently doesn't open up a gap.
What do you mean by "open up a gap"? Like actually pull the rim seam apart slighly due to the circumferential tension applied by the pads?

Regarding the OP's question, I'm not familiar with your rims, but I agree that it is most likely rim seam related, although there may be exacerbating circumstances that make it more noticable. Rim irregularities can often be smoothed with a little emery cloth on a sanding block, but that assumes there are no other issues.

mattr
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Location: The Grim North.

by mattr

No.
Heavy braking, more pressure on the pads, makes the step in the braking surface large enough to catch on the pads. And click.

yinya
Posts: 158
Joined: Tue Aug 07, 2007 9:06 pm

by yinya

Thanks for all the input. I checked all visually, looks normal. I am also using rim plugs instead of tape, but doubt that has much to do with it? Quick release is same I use with other wheels, no noise there.

And yes, definitely can feel the up and down (to the side) of the rim when run finger on it on the ride. The faster the speed, the higher the frequency of clicking.

Next step I will try is to see if mechanic can get the rim to be more true.


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Calnago
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by Calnago

Should have said this at the beginning, but it might even just be the valve stem knocking against the valve hole in the rim. Try taping it down. Also, make sure the presta valve top is snug and not loosened off in the position to accept air.
Colnago C64 - The Naked Build; Colnago C60 - PR99; Trek Koppenberg - Where Emonda and Domane Meet;
Unlinked Builds (searchable): Colnago C59 - 5 Years Later; Trek Emonda SL Campagnolo SR; Special Colnago EPQ

yinya
Posts: 158
Joined: Tue Aug 07, 2007 9:06 pm

by yinya

Hah! Great point, the slight out of trueness could easily get the valve to bounce. Will try this next.


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Calnago
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by Calnago

A loose valve will click regardless of whether the wheel is perfectly true or not. Or simply a presta valve that’s been left open. If the latter, then simply screw down the cap and say, “boy, that was dumb”. If it’s closed, but the hole in the rim is large enough that the valve can be wiggled but hand enough to make it “tap” the sides, then just tape the valve down to the rim. The simplest thing here is just to take a 2” piece of electrical tape then put it over the valve and just push it on over till the valve pops through, then pull it down to the base and adhere each side of the tape to the rim.
Colnago C64 - The Naked Build; Colnago C60 - PR99; Trek Koppenberg - Where Emonda and Domane Meet;
Unlinked Builds (searchable): Colnago C59 - 5 Years Later; Trek Emonda SL Campagnolo SR; Special Colnago EPQ

by Weenie


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