Bent (carbon) wheel...

[dd74]

D'oh!

Stage 5 (I think this was) in the Tour de Suisse, and during a sprint finish, Mark Cavendish and another rider collide. Check out Cavendish's front wheel, which is carbon.

First of all, I thought carbon would snap, not bend.

Second of all, a petition is going around to get Cavendish thrown out of the upcoming Tour de France for this action.

My take: boogity boogity, that's racing, boys!

[Leland Pate]

I'm almost certain it did snap. If you had some "after" shots of the wheel, I bet it's in at least two parts.

[greglepore]

Check out the vid on Youtube-Cav went maybe 10 meters sideways-initially it looks like the other guy also did, until you realize Cav hooked his bars and pulled him over. It was stupid sketchy.

[David]

I assume Cavendish is the guy in yellow. Totally his fault. What did he think was going to happen cutting across the other riders?

[island911]

Maybe, the wheel was stuck to a piece of some sort of flexible material. .. like rubber.


. . .maybe.

[tangerine911S]

Originally Posted by Leland Pate

I'm almost certain it did snap. If you had some "after" shots of the wheel, I bet it's in at least two parts.

I had seen the video before this thread and it looked like the wheel snapped back into shape. I too assumed it would have snapped in two

[Leland Pate]

Yup, those tubular tires are literally glues to the rim.

[dd74]

The rubber part (the tire) is very thin; maybe 23mm wide at the most, maybe even 20mm.

The entire rim, including the spokes, is carbon. The hubs are plain (but high end) aluminum (Dura Ace).

The wheels are $4,500 a pair, FWIK.

[island911]

The wheel still spinning? (centrifugal effect)

The structure of the (reinforced) tire would still be in tact.

And, not all of the CF would likely strain to failure.

[Tobra]

the guy in black in the middle, amazing he made it through that without crashing

[porsche4life]

A very good source says that the strain in a direction the wheel was not designed to handle caused the CF to de-laminate... Hence making the wheel look broken with no fibers flying....

[dd74]

So, I'm very confused now. Do the engineers here think the wheel is toast? It clearly bent (deformed?), then, though I haven't seen the video of it doing so, bent back.

I've heard these carbon wheels can be cracked, spokes broken, and run over by all but a truck, and still be ridden on.

Again, the carbon wheel is one piece, spokes included, FWIK.

Last year during the Tour de France, a rider hit an abutment at the end of a roundabout, at about 30 mph. His bike (carbon) literally exploded beneath him. He was fine, btw.

But, of course, a carbon frame isn't round, though most now are usually monocoque which helps their resiliency...supposedly.

[porsche4life]

Wheel is trash from my understanding... The Carbon and resin separated... Likely just centrifugal force that makes it appear round again...

[dd74]

Right. I forgot about the resin. Which is, by the way, a big buyer beware when buying used carbon bikes. If a cut is deep enough into any of the frame (past the resin), walk away.

[greglepore]

While on the subject of carbon bikes, there's been a rash of carbon steerer failures reported lately. Trek, at least, claims its due to a combination of stems with large internal cutouts coupled with overtorque on the clamp bolts. Personally, I think there should be an insert in the steerer-AME did this with their first superlight forks, you glued an aluminum sleeve in the steerer after you determined the length (it also was tapped for the cap bolt).

Steerer failure is nasty, instant trip to the pavement. In fact, the whole failure mode of carbon is nasty, period, when it comes to forks-I'm personally aware of a couple of instances where blades simply sheared off. One of these riders got a helicopter ride after.

[island911]

Originally Posted by porsche4life

A very good source says that the strain in a direction the wheel was not designed to handle caused the CF to de-laminate... Hence making the wheel look broken with no fibers flying....

I don't know the specifics of the construction (fiber orientation) of that wheel but I doubt the failure was (primarily) a delamination. If delam was primary source of failure then I would say the design sucks -- I doubt that.

My guess is that one side of the wheel (compression side /up-side in photo) stayed intact enough to act as a hinge. Where as the opposite side had a sharp break (fibers) at the load focus. ...and with that big 'rubber-band' (tire) doing it's part, what's left is pulled closed again.

[gtc]

Originally Posted by dd74

So, I'm very confused now. Do the engineers here think the wheel is toast? It clearly bent (deformed?), then, though I haven't seen the video of it doing so, bent back.

I've heard these carbon wheels can be cracked, spokes broken, and run over by all but a truck, and still be ridden on.

Again, the carbon wheel is one piece, spokes included, FWIK.

Last year during the Tour de France, a rider hit an abutment at the end of a roundabout, at about 30 mph. His bike (carbon) literally exploded beneath him. He was fine, btw.

But, of course, a carbon frame isn't round, though most now are usually monocoque which helps their resiliency...supposedly.

The wheel is toast... beyond a shadow of a doubt. The delamination theory seems plausible assuming a traditional layup construction, though the best rims I've seen in the past are not made this way.
Most carbon rims are so stiff that you will break spokes before you break the rim itself. And because of this stiffness, it's possible to continue riding with a broken spoke.... something not possible just a few years ago (you'd get awful brake rub, or the wheel would just taco).

I would never, ever, ride a carbon wheel with even the smallest crack. Look up what happened to the old Spinergy wheels when they failed.... it was very bad, basically an explosion followed by an instantaneous faceplant.