Cracking carbon rims

[nick_the_wheelbuilder]

I just thought I'd share an experience with you.

 

I build a bunch of wheels and also do repairs and rebuilds.

A customer brought a wheel for repair - he was breaking nipples.

 

The rim is not branded and is laced to a Hope hub. 

 

On inspection I found that the rim was deforming and cracking at a few nipple holes. Upon even closer inspection, I found the spoke threads exposed, indicating that the spokes used in the original build are too short by a few mm. As the spokes were too short, the heads of the nipples were not properly supported and were popping off.

 

I measured the spoke tensions and they were all over the place, some tensions way too high, and some very low.  I had to decline to rebuild the wheel as I'm afraid the rebuild process, releasing all tension and then adding tension to the rim again will cause it to fail.

 

I'm interested in your thoughts.

 

 

 

 

[CAAD4]

Another reason to use a good wheelbuilder, like you, who won't take shortcuts

 

You have just saved someone's front teeth or maybe even their neck by saying "no thanks". ..

[Martin PJ]

I think you are right, the rim is probably damaged all over, even if it looks fine.

[droo]

Wouldn't touch it with a rented barge pole.

 

Do it properly (new rim and spokes) or not at all. Otherwise when it fails (and it will), you'll be the last oke who touched it.

[GrahamS2]

I found the spoke threads exposed, indicating that the spokes used in the original build are too short by a few mm. As the spokes were too short, the heads of the nipples were not properly supported and were popping off.

 

Explain this part to me please? Does the head break if not held by the thread? Never built a wheel, so not familiar with the 'right' way to do it. 

[Rigardt@Scott]

So what did the client end up doing? I would not ride those wheels at all - I think it was the responsible thing to decline to rebuild them...

[Skinnyone]

Explain this part to me please? Does the head break if not held by the thread? Never built a wheel, so not familiar with the 'right' way to do it. 

In a nutshell, yes. A correctly built wheel would see the spoke thread going all the way through the nipple even by a couple of mm. 

 

I have had a case where the nipple pulled through the rim whilst de-tensioning the wheel because the tension on some spokes was so high on some spokes - when releasing the "balancing tensions" the rim gave way....guess who had to pay for a new rim....

 

You did the right thing by not trying to save what is effectively scrap...

[droo]

I have had a case where the nipple pulled through the rim whilst de-tensioning the wheel because the tension on some spokes was so high on some spokes - when releasing the "balancing tensions" the rim gave way....guess who had to pay for a new rim....

 

 

And from this you learned to slack off the tight ones first...

 

This is one of the reasons I generally detension spokes when stripping a wheel rather than cutting them. You can bend a rim if you cut spokes in the wrong sequence.

[Skinnyone]

And from this you learned to slack off the tight ones first...

 

This is one of the reasons I generally detension spokes when stripping a wheel rather than cutting them. You can bend a rim if you cut spokes in the wrong sequence.

True, I was going from the valve hole and moving around the rim....

[nick_the_wheelbuilder]

So what did the client end up doing? I would not ride those wheels at all - I think it was the responsible thing to decline to rebuild them...

 

He decided to ride them, but insure the bike 

 

I replaced the broken nipples and left it at that, after explaining the situation and making sure he understood the risks.

[shaper]

He decided to ride them, but insure them

 

I replaced the broken nipples and left it at that, after explaining the situation and making sure he understood the risks.

Hope you got something in writing that the Client agreed to !

[Rigardt@Scott]

He decided to ride them, but insure them

 

I replaced the broken nipples and left it at that, after explaining the situation and making sure he understood the risks.

Sho.... sneaky sneaky. That's called insurance fraud on the client's behalf. You can't insure something that is broken, and I'm pretty sure if he specified that it was cracked the insurer would decline to insure the rims.

 

Anyway, at least you did the right thing.

[Eugene]

He decided to ride them, but insure them

 

I replaced the broken nipples and left it at that, after explaining the situation and making sure he understood the risks.

Insured wheels already broken?

[nick_the_wheelbuilder]

Insured wheels already broken?

 

Edited my post - actually he said he'd insure the BIKE. 

[madbradd]

Crazy to take that risk given the replacement cost of non-branded rims. 

[Carmichael]

Hijack - i have dark horse carbon rims on TT bike. There is a small bulge on one side at brake lining. Is this n big problem? Can is till ride with it or is it time to claim from insurance? Have IM this weekend dont know what to do if it is ok or if i must swopped with road bike rims.

 

Thanks