Is "light weight" carbon wheel not strong enough for a hard braking?

Discussion in 'Cycling Equipment' started by alpha2k, Jul 18, 2007.

  1. alpha2k

    alpha2k New Member

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    From the TDF video(stage 8?), I saw a front "light weight" carbon wheel was dramatically broken by an emergent hard braking. The TMO rider was trying to avoid the collision with a dog acrossing the road.

    Is the light carbon wheel supposed to be so? Or should rider keep the wheel straight along the movement when he was applying the brake?

    What do you think?
     
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  2. bobbyOCR

    bobbyOCR New Member

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    The wheel broke because carbon parts are generally designed to be strong against one load direction, in this case, vertically. They are laterally stiff, but aren't designed to tolerate side-loading. Don't let this detract from perceived quality of these wheels. Carbonsports know what they are doing when it comes to wheels.

    The wheel would have been fine if he kept going straight, but the dog would have been in a bit of pain.

    and for reference, the model of wheel is 'lightweight', in specific, the one that broke was the Lightweigh Obermayer. They are like ksyriums, made of carbon, and better in every way. they just have a long list of various words (or in mavic's case, letters) after the original model name.

    in case that made no sense, it didn't to me, just call 'em lightweights.
     
  3. hd reynolds

    hd reynolds New Member

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    I think the wheel that broke was a Lightweight Ventoux and not an Obermayer.
     
  4. dhk2

    dhk2 Active Member

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    Wait, didn't the wheel break when he hit the dog? I didn't see the video replay, but in the photo's it appears the wheel was fine until it contacted the large dog. For any wheel to fail because of hard braking would be totally unacceptable, IMO.
     
  5. alpha2k

    alpha2k New Member

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    Checked the video again. The TMO rider began to brake several meters before the dog. The front wheel was turned to right as soon as it hit the dog and then the wheel began to break. I don't think it was the collision with the dog kill the wheel, because the dog looked fine and walked away easily after the crash.

    I understand the carbon fiber is normally designed to be strong only in one direction and a lot of carbon components from a bicycle are weak on side load, such as rim, fork, frame... But are light carbon wheels safe enough for a fast tight turn on hill descent(in worst case, have to brake, the road begins to tilt up in the turn...)? My understanding is that Alu wheels, like ksyrium sl, eurus, will not do the same.
     
  6. fish156

    fish156 New Member

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    Not even close. Next time you look at any set of Kysriums you should notice that they are alloy, not carbon, as you have stated.

    As for "better", you may have noticed that stages 9 and 11 of the Tour were won by Barloworld team members and they are running on Mavic R-Sys and Cosmic Carbone Ultimate wheels. So, whether you like them, or not, there are some pretty important races being won on the latest Mavic wheels by a wildcard team - one on a tough mountain stage and one in a sprint finish.
     
  7. fish156

    fish156 New Member

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    You are absolutely right. That wheel was being braked very hard and was turned hard just before it folded up. I think almost any wheel would fold up given the same set of circumstances, dog, or not.
     
  8. tfstrum

    tfstrum New Member

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    Looks like the hard dog broke the wheel. That and the guys weight on the wheel as he was turning the bars and going over the top.
     
  9. alpha2k

    alpha2k New Member

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    From my experience on my wheels, the tire will slip on the ground before the rim begins to fold when I brake hardly. What tires the TMO guy was using? I want a pair for my crits race so I don't need to slow down too much in the corner.
     
  10. Rich8P

    Rich8P New Member

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    I'm not a lawyer but I can expect it won't be too long before a rim designer is in court and a cyclist is claiming that a turn-and-brake manoever is part of normal and predictable user (rider) behavior. If the rim really broke before he hit the dog, then IMO it broke under predicable usage conditions.

    Doesn't France enforce sloppy engineering judgement under criminal law? I seem to remember a manslaughter case in the news when Ayrton Senna's steering rack broke. I think the race car case was aquitted because it wasn't proven that the steering rack caused the crash but there are disturbing parellels.

    Perhaps you can argue that pros understand the risks of lightweight equipment but I doubt they have a good risk perception or much engineering knowlege.

    I once designed special tyres for a tuned Jaguar. When it came to testing time the pro test driver wasn't convinced. He just handed me the keys and said 'you first'. Nothing like driving untested tyres at 170mph to straighten out any bad engineering judgement.

    I don't see much difference between this and doping if you are using something that increases risk to the body to gain a few milliseconds in a time trial.

    My hope is that the equipment that I'm buying is capable of functioning properly on the road. Since my rims are cheep ones (Mavic Askim) and probably quite heavy compared to the pro equipment, I hope that they have a little more safety margin. Difficult to test that theory though.
     
  11. bobbyOCR

    bobbyOCR New Member

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    Now, you've misunderstood me once, and completely got it wrong once. I was meant to say 'except made of carbon'. I was implying that the only similarity is the same model name with suffixes.

    You call on the R-SYS and Cosmic carbone is true, but invalid. Neither of those wheels were Ksyriums.

    And they were definitely Obermayers. All the T-Mobile team used Obermayers, none used Ventoux.
     
  12. bobbyOCR

    bobbyOCR New Member

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    I think they use continentals with black chili. But you are forgetting that it was completely front weighted. This massively increases the traction. It was also given a larger footprint in the forward direction as he turned it sideways.
     
  13. alpha2k

    alpha2k New Member

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  14. Rich8P

    Rich8P New Member

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    In the best case (slick tyres and smooth road) Completely front weighted doesn't actually increase traction, unless you get downforce created by something other than weight (e.g. an aerofoil).

    It actually reduces stability (if the back wheel comes right off the road then equilibrium is with the bike in reverse).


    Not sure that this should have an effect. Friction is uR, where u the friction coefficient and R the resultant force. Area is not a factor of maximum friction because you aren't skidding.
     
  15. Skoorb

    Skoorb New Member

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    I watched that video on youtube and paused just before impact. I see no bending in the wheel; I believe the wheel buckled because it hit the dog, not because of braking.
     
  16. bobbyOCR

    bobbyOCR New Member

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    Carbon tends to not bend. Especially the resin used in lightweights, it tends to be more brittle.

    Once again, if you look closely it broke before the dog.
     
  17. Skoorb

    Skoorb New Member

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    All I see on the frame before impact is that he has turned in wheel in an instinctive attempt to turn away but it still seems totally straight and unbroken.
     
  18. Tech72

    Tech72 New Member

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    Excellent post. I was thinking the same when I saw the wheel buckle under what I would also consider a normal, predictable manoever, an action one might have to do during a race/ride (hopefully not too often). I realize carbon wheels like the Lightweights are designed with specific loads and performance criterias in mind but the braking action of the TMO rider does not seem out of the ordinary. Also consider that these wheels are sold around the world to consumers (not pros) that are on average heavier than a pro rider. If the wheel can buckle as shown in the video footage under a 150lbs rider, what happens when a +180lb rider does a similar braking manoever? I always wanted a pair of Lightweights but am not so convinced anymore, just to save weight but risk my arse and losing a large amount of $$$$. Ok, I still want a pair of Lightweights but.......
     
  19. bobbyOCR

    bobbyOCR New Member

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    How often do you turn a wheel 80 degrees to emergency stop while travelling at a presumably high speed of 40+km/h? It is not an emergency braking maneuver and if he had continued straight, he would still have crashed but the dog would have been nastily injured and the wheel would have been absolutely fine. In a situation like that, there was no way to avoid crashing.
     
  20. dhk2

    dhk2 Active Member

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    Watched the video several times as well. Agree the front wheel turned to the right and buckled after it hit the dog. Guess we all have different opinions when watching the same video, but I just don't see the wheel turning or failing until it contacted the big dog.
     
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