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"Carbon would have bounced back"

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"Carbon would have bounced back"

Old 01-09-19, 10:39 AM
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TimothyH
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"Carbon would have bounced back"

Shimano C24 wheels. These are the hybrid carbon/aluminum wheel. The alloy skeleton is thinner than a standard aluminum wheel and crabon is laminated on top of that. It isn't full crabon.

So I hit a pot hole and it needed to be trued. I brought it to an experienced mechanic whom I trust. He did the best he could but it is still out of round. A section of the rim about two inches long is dented in toward the hub by less than 1 mm. 16 spokes are too far apart to pull the section of rim.

"Carbon would have bounced back" was what he said.

What say you? Would it have bounced back?


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Old 01-09-19, 11:15 AM
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Probably.
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Old 01-09-19, 11:36 AM
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Did the rim actually make contact with the ground, ie is there road rash on the rim? If not then yea the carbon rim probably would have bounced back
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Old 01-09-19, 12:06 PM
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I never understood mixing CF and aluminum for rims. Logically, either all aluminum or all CF would be stronger on impact. CF is a high modulus, very strong material that cannot handle a large yield. Aluminum is low modulus. You have to deflect aluminum a lot for it to be doing any work to support the load or impact. So, with a mix of the two, by the time the aluminum is doing anything, the CF has already failed. Yes, the rim is still in one piece and you are still riding safely, but the rim is no longer round or the original strength.

(Now aluminum braking surfaces are another matter. I can see that, but the aluminum there should not be considered structural, merely a sacrificial braking surface.)

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Old 01-09-19, 12:08 PM
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On the other hand, a rim with a decent number of spokes might not have bent at all. I still build my wheels for 36 spokes, being a curmudgeon.
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Old 01-09-19, 12:17 PM
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Originally Posted by redlude97 View Post
Did the rim actually make contact with the ground, ie is there road rash on the rim? If not then yea the carbon rim probably would have bounced back
If the tire pinches (with or without a flat) the pothole edge is hitting the rim directly with virtually no padding from the thin, hard rubber and sidewall, but there will be no road rash. Usually hitting like this will cause the characteristic "snake bite" two holes but not always even with tubes and rarely with sewups. Never ridden tubeless so I cannot say what happens there. In my sewup days, I dented more than a few rims and don't recall ever seeing road rash. Usually did not flat. (Finished a race once on two dented rims (RR tracks) and twice road home on sewup rims with 2" dents. Did flat once in a race on RR tracks with no rim damage, so there is no "always".)

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Old 01-09-19, 12:20 PM
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Originally Posted by 79pmooney View Post
I never understood mixing CF and aluminum for rims. Logically, either all aluminum or all CF would be stronger on impact. CF is a high modulus, very strong material that cannot handle a large yield. Aluminum is low modulus. You have to deflect aluminum a lot for it to be doing any work to support the load or impact. So, with a mix of the two, by the time the aluminum is doing anything, the CF has already failed. Yes, the rim is still in one piece and you are still riding safely, but the rim is no longer round or the original strength.

(Now aluminum braking surfaces are another matter. I can see that, but the aluminum there should not be considered structural, merely a sacrificial braking surface.)

Ben
You can't really build a 45+mm deep aluminum wheel that is in a competitive weight range. Most of the hybrids the carbon fairing isn't structural, i believe only shimanos are. Not sure how you're build a nonstructural aluminum brake track with a structural carbon core. I do agree from a strength perspective that one of the other is going to be stronger.
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Old 01-09-19, 12:24 PM
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Originally Posted by 79pmooney View Post
If the tire pinches (with or without a flat) the pothole edge is hitting the rim directly with virtually no padding from the thin, hard rubber and sidewall, but there will be no road rash. Usually hitting like this will cause the characteristic "snake bite" two holes but not always even with tubes and rarely with sewups. Never ridden tubeless so I cannot say what happens there. In my sewup days, I dented more than a few rims and don't recall ever seeing road rash. Usually did not flat. (Finished a race once on two dented rims (RR tracks) and twice road home on sewup rims with 2" dents. Did flat once in a race on RR tracks with no rim damage, so there is no "always".)

Ben
Yes, but generally with a carbon rim that level of cushioning is enough to protect the carbon which is susceptible to impact damage but deforms elastically. You'll snakebite but the rim will generally be fine. Carbon rims hardly ever need to be trued
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Old 01-09-19, 01:00 PM
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Originally Posted by redlude97 View Post
Did the rim actually make contact with the ground, ie is there road rash on the rim? If not then yea the carbon rim probably would have bounced back
Nope. Rim did not contact the road. The tire pinch flatted but appears to have potected the rim.


Originally Posted by redlude97 View Post
Yes, but generally with a carbon rim that level of cushioning is enough to protect the carbon which is susceptible to impact damage but deforms elastically. You'll snakebite but the rim will generally be fine. Carbon rims hardly ever need to be trued
This is what I'm after.

Trying to figure out if I spend the money to re-lace the wheel, buy a new wheel or spend the extra for carbon.

Thanks.

Good posts from all.



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Old 01-09-19, 01:39 PM
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Carbon may of bounced back or it could of cracked, you will never know.
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Old 01-09-19, 02:16 PM
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If they were Chinese carbon rims, they would have assploded and you would be in the grave right now.
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Old 01-09-19, 02:46 PM
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Originally Posted by Dean V View Post
Carbon may of bounced back or it could of cracked, you will never know.
Of course, but we can look at similar past events and speculate on what might have been likely.

I'm sure I'm not the first person to have run a front wheel into a pot hole, carbon or otherwise.


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Old 01-09-19, 04:14 PM
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You might never know with a carbon rim if it suffered enough non-visible damage that compromised the wheel integrity. So an advantage with aluminum in that case, at least you can see it's toast.. Kind of like a carbon bike that was crashed, would you buy it used if you knew ?.

I'd be replacing the wheel with a DA replacement.
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Old 01-09-19, 04:33 PM
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Yes, I think pay the money for a new rim or wheel and let this one go. @79pmooney gives good (to me) reasons for not getting another hybrid rim, though if you still have one or more, keep riding it or them.
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Old 01-09-19, 05:28 PM
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Originally Posted by Aubergine View Post
On the other hand, a rim with a decent number of spokes might not have bent at all. I still build my wheels for 36 spokes, being a curmudgeon.
Possibly.

However, remember that the hub hangs on the spokes.

The actual spokes don't support the rim on the bottom, although they do help keep the rim round through tension.

But, a gazillion spokes might not protect the rim at a point impact because they aren't actually holding the rim outward.

Originally Posted by TimothyH View Post
Nope. Rim did not contact the road. The tire pinch flatted but appears to have potected the rim.
In other words, the rim DID ACTUALLY SLAM AGAINST THE ROAD (POTHOLE). That is what the pinch flat is.

The tire may have kept the rim from being marred, but the rim did take the force of the impact with the road.
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Old 01-09-19, 05:32 PM
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in a word - yes. Alloy bends when it hits obstacles. There's really no fixing it. I do a lot of rim swaps for that reason. Doesn't happen with carbon. Really one of the big features in my world when in many cases the carbon and alloy rims are near same weight. I deal with a lot of racers and racers hit things - especially in cross. Carbon does way better.

That said when you exceed carbon it just breaks. Rest assured that the same impact would have destroyed an alloy wheel as well.
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Old 01-09-19, 05:38 PM
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I assume many people have seen the "Road Bike Party" clips. There are a bunch of them.


And, as I understand it, there were a few "outtakes", but the wheels really held up well. A few more spokes than some road wheels, but Carbon Fiber nonetheless.
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Old 01-09-19, 05:57 PM
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Originally Posted by Aubergine View Post
On the other hand, a rim with a decent number of spokes might not have bent at all. I still build my wheels for 36 spokes, being a curmudgeon.
Bingo. Low spoke count alloy wheels make it more likely to have a wheel impossible to really true again.
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Old 01-09-19, 06:00 PM
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Originally Posted by CliffordK View Post
I assume many people have seen the "Road Bike Party" clips. There are a bunch of them.

https://www.youtube.com/watch?v=7ZmJtYaUTa0

And, as I understand it, there were a few "outtakes", but the wheels really held up well. A few more spokes than some road wheels, but Carbon Fiber nonetheless.
Did you mean carbon fiber hybrids?
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Old 01-09-19, 06:49 PM
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Originally Posted by TimothyH View Post
Of course, but we can look at similar past events and speculate on what might have been likely.

I'm sure I'm not the first person to have run a front wheel into a pot hole, carbon or otherwise.


-Tim-
Renshaw did at the Tour of California years ago. Front end disinigrated.
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Old 01-09-19, 06:57 PM
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Originally Posted by colnago62 View Post

Renshaw did at the Tour of California years ago. Front end disinigrated.

There was also that incident at Tirreno Adriatico's TTT....where Team Sky's TTT train hit a pothole...and there was lots of broken carbon fiber wheels. Shimano traced the error back to out-of-spec tubular being used IIRC...

http://www.cyclingnews.com/news/whee...ico-ambitions/

https://road.cc/content/news/218799-...-broken-wheels
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Old 01-09-19, 07:41 PM
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Originally Posted by colnago62 View Post
Renshaw did at the Tour of California years ago. Front end disinigrated.
Originally Posted by Marcus_Ti View Post
There was also that incident at Tirreno Adriatico's TTT....where Team Sky's TTT train hit a pothole...and there was lots of broken carbon fiber wheels. Shimano traced the error back to out-of-spec tubular being used IIRC...
Were not both of these due to tubulars coming off the wheel and the carbon rolling directly on the pavement? I'm sincerely asking, not trying to challenge.

The same thing did not happen to me. Both clinchers stayed inflated and on the rim during the impact and until I rolled to a stop. About 15 seconds after I stopped I heard the pffffffffffft of the rear tube failing. About 5 seconds later I heard the front let go too. The rims never touched pavement directly.


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Old 01-09-19, 07:44 PM
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Originally Posted by Psimet2001 View Post
in a word - yes. Alloy bends when it hits obstacles. There's really no fixing it. I do a lot of rim swaps for that reason. Doesn't happen with carbon. Really one of the big features in my world when in many cases the carbon and alloy rims are near same weight. I deal with a lot of racers and racers hit things - especially in cross. Carbon does way better.

That said when you exceed carbon it just breaks. Rest assured that the same impact would have destroyed an alloy wheel as well.
Thanks for this.


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Old 01-09-19, 07:48 PM
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Originally Posted by TimothyH View Post
Were not both of these due to tubulars coming off the wheel and the carbon rolling directly on the pavement? I'm sincerely asking, not trying to challenge.

The same thing did not happen to me. Both clinchers stayed inflated and on the rim during the impact and until I rolled to a stop. About 15 seconds after I stopped I heard the pffffffffffft of the rear tube failing. About 5 seconds later I heard the front let go too. The rims never touched pavement directly.


-Tim-
As far as the Tirreno-Adriatico...Shimano's verdict was basically, "RTFM"--the wheel was by spec designed for 25mm tubulars and no narrower...and the Team Sky wrenches put 23mm tubulars on, and didn't go any further into it publicly. Which is the kind of thing I'd think they'd have known about. But oh well.

https://www.velonews.com/2017/06/new...tirreno_439821
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Old 01-09-19, 07:53 PM
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I've cracked four carbon rims on holes: A Zipp 303, a Zipp 404, a Hed Stinger 6, and a Neuvation 50mm. All tubulars. Flatted the new tire on the neuvation, but all the other tires were fine.

So, in my experience, no. Carbon doesn't bounce back. It just cracks loudly and makes for an expensive replacement.
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