TimothyH

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?


-Tim-

popeye

Probably.

redlude97

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

79pmooney

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

Aubergine 

79pmooney

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

redlude97

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.

redlude97

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

TimothyH

Nope. Rim did not contact the road. The tire pinch flatted but appears to have potected the rim.


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.



-Tim-

Dean V

Carbon may of bounced back or it could of cracked, you will never know.

Sojodave

If they were Chinese carbon rims, they would have assploded and you would be in the grave right now.

TimothyH

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-

Steve B.

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.

noglider 

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.

CliffordK

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.

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.

Psimet2001 

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.

CliffordK

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.

Marcus_Ti

Bingo. Low spoke count alloy wheels make it more likely to have a wheel impossible to really true again.

redlude97

Did you mean carbon fiber hybrids?

colnago62

Marcus_Ti

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...

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

https://road.cc/content/news/218799-...-broken-wheels

TimothyH

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-

TimothyH

Thanks for this.


Tim-

Marcus_Ti

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

rubiksoval

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.