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Shimano carbon rim clean coat bubbling up around nipples.

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Shimano carbon rim clean coat bubbling up around nipples.

Old 12-07-20, 01:29 PM
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purdyd
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Shimano carbon rim clear coat bubbling up around nipples.

I have a set of shimano wh r9170 c40 to r12 rims.

and the clear coat is coming off around the nipples.

this is actually the second set this has happened to me on.

I believe it is related to braking because I babied this set along for a year and after a technical descent with hard braking I noticed it started.

it is now quite severe looking. Worse on the front wheel than the back.

anyone seen something like this?





Last edited by purdyd; 12-07-20 at 01:39 PM.
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Old 12-07-20, 04:38 PM
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What is the spoke tension?
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Old 12-07-20, 06:17 PM
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Good question Iíve never adjusted the spokes as their has never been any need. They are disc brake wheels and they have always seemed true so spoke tension is straight from the factory.
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Old 12-07-20, 10:03 PM
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This looks much like the typical carbon frame joint/"braze on" bonding problem that plagued early carbon frames. Andy
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Old 12-07-20, 11:06 PM
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Originally Posted by Andrew R Stewart View Post
This looks much like the typical carbon frame joint/"braze on" bonding problem that plagued early carbon frames. Andy
Iím not sure what that means or how it applies to this.

itís interesting that there is a general diagonal shape to the clear coat crinkling. I suspect it is flexing in the carbon rim and the clear coat Is not flexible enough and cracks.

i donít know if this is just me and I can do something different or just an issue with this particular shimano wheelset

disc brake on right


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Old 12-09-20, 07:43 AM
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I have no experience with these, but is there anything applied around the tire that might be leaking through? What does it look like on the tire side of the wheel?
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Old 12-09-20, 08:46 AM
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As a LAST RESORT, you may use some ~1000grit sandpaper to wet-sand the affected area. While sanding, often check the dust you just sanded off:

1. If it's white, it means it's clearcoat. Keep sanding.
2. If it's black, you just hit carbon. STOP.

Now change to a finer sand paper like 3000. Carefully smooth out the area and inspect:

1. If there is no sign of cracking, fraying and/or softness when pressed hard with fingernail, it's probably fine. Clearcoat damage only.
2. If the carbon shows any damage, well, you are SOL I'm afraid.
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Old 12-09-20, 08:57 AM
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Originally Posted by Geepig View Post
I have no experience with these, but is there anything applied around the tire that might be leaking through? What does it look like on the tire side of the wheel?
the tire side is immaculate. I do use sealant and tubeless tires. But there is rim tape snd each spoke hole is also sealed with what looks like and aluminum tape. There is no sign of damage on the spoke bed inside.

you can scrape the clear coat off with a fingernail and the underlying carbon appears to be fine.

it appears there maybe a slight amount of galvanic corrosion on the side of the nipple where it contacts the side of the hole.
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Old 12-09-20, 09:34 AM
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Originally Posted by Dante49 View Post
As a LAST RESORT, you may use some ~1000grit sandpaper to wet-sand.
the clear coat just comes off with the scrape of a fingernail in the affected areas and you can even keep going with some more effort.

and there doesnít appear to be any underlying damage to the carbon

itís going to be warrantied so now I am trying to figure out how I can prevent this from happening again


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Old 12-09-20, 12:15 PM
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Titanium is less susceptible to galvanic corrosion with carbon. Maybe replace nipples with Ti nipples?
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Old 12-09-20, 12:17 PM
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I bet it's corrosion caused by sealantÖhere is my educated guess:

Some quick searches suggest that ammonia in the sealant will eat paint, which includes clear coat. The sealant somehow found its way out by passing the rim tape and some aluminum tape. The leakage just kept going and eating away clear coat near the places it came out: spoke holes.
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Old 12-09-20, 01:47 PM
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Originally Posted by Dante49 View Post
I bet it's corrosion caused by sealantÖhere is my educated guess:

Some quick searches suggest that ammonia in the sealant will eat paint, which includes clear coat. The sealant somehow found its way out by passing the rim tape and some aluminum tape. The leakage just kept going and eating away clear coat near the places it came out: spoke holes.
Maybe but it would have to get by the tape, and the stainless tape, apparently it isnít aluminum. I didnít see any evidence of sealant inside the wheel.

I see no other sign of corrosion including the surfaces that are in constant contact with the sealant. In fact it has been my experience carbon wheels do well with sealant, much better than aluminum rims.

but ammonia certainly could be part of the issue. I think we would see it on other carbon wheels? Anyone?
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Old 12-09-20, 01:56 PM
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Originally Posted by purdyd View Post
I suspect it is flexing in the carbon rim and the clear coat Is not flexible enough and cracks.
i donít know if this is just me and I can do something different or just an issue with this particular shimano wheelset
I think this is the issue. The asymmetric braking force from the disc is probably increasing the spoke tension, causing the nipple to flex. The clearcoat can't take it.

I think it's a fundamental issue with these wheels and you. My advice would be get the wheels warrantied, but immediately sell them (as new unmounted) and replace with something else. For whatever reason, you and these wheels don't mix.
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Old 12-09-20, 07:12 PM
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Originally Posted by gsa103 View Post
I think this is the issue. The asymmetric braking force from the disc is probably increasing the spoke tension, causing the nipple to flex. The clearcoat can't take it.

I think it's a fundamental issue with these wheels and you. My advice would be get the wheels warrantied, but immediately sell them (as new unmounted) and replace with something else. For whatever reason, you and these wheels don't mix.
that is some pretty solid and frank advice. Thanks.
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