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  1. #1
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    GCN tests Road, CX, & MTB on cobbles

    Thought this video was pretty interesting: https://www.youtube.com/watch?v=QvO74sZxVs4

    I wish they had tested a FS XC bike too. Perhaps the rear suspension would have added further efficiency gains. It was interesting to note that they said on the MTB both of them averaged the lowest wattage yet both went the fastest despite both being in the least aerodynamic position of the 3 bikes.

    This test reminds me of how a few years ago, when those Niner rigid bikes were popular, people kept asking why don't the pros race 15lb rigid bikes at WCs and LMN just kept saying it was because they are slower.

    I think there is some confusion as to how bumps work. I haven't exactly studied it but I think what happens is that any time you encounter a bump you are forced to transfer forward kinetic energy into vertical kinetic energy, which becomes potential energy that is largely not recaptured into forward kinetic energy. When you hit a table top jump, and you land on the back side perfectly--when it feels like you barely even landed--you recapture much of your forward KE, however 99% of the time the landing isn't ideal and you lose that energy. The cobbles, or any bump really, is the same thing just at a smaller scale. I imagine on the cobbles it can be the worst case scenario--you clear the table top, and the landing, and then smash into the next take off. The difference between what happens on a rigid bike and what happens on a suspended bike is that on a suspended bike the mass that is accelerated upwards is much lower--unsprung mass--thus preserving forward kinetic energy. It becomes much smoother, and can feel slower as a result--don't forget, smooth is fast!

    Now obviously there are other benefits to suspension (confidence and grip in bumpy corners, braking, climbing traction etc) and don't forget that tires are part of your suspension, so harder smaller tires that deflect less is basically the same thing as less suspension. So I'm sure some people will argue that the GCN result is basically only down to the larger tire--which is why I would have liked to see more testing.

  2. #2
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    Sometimes I feel like GNC videos as old Top Gear. You watch them for the comedy, but hardly any scientific value in it. They can be even worse as they rely heavily on sponsorship and no doubt they will skew results to please their supporters.

    I do however, believe that improved traction is faster despite the weight tradeoff (HT vs FS) usually. Still, rolling resistance and aerodynamics will play an important part, in a less manner in mtb though.

  3. #3
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    Yeah, this isn't scientific, but feelings are even less rigorous than these kinds of tests. You can get good enough results to satisfy your intent a lot easier than to produce a paper for a journal.

    I think you'd have a really hard time disproving their conclusion: the lower rolling resistance was great enough to overcome both a power and aerodynamic disadvantage. The biggest problem with their test is how well they maintained the same line, it's possible that on the third attempt they had found a better line. Also the wind could have changed.

  4. #4
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    Quote Originally Posted by litany View Post
    Yeah, this isn't scientific, but feelings are even less rigorous than these kinds of tests. You can get good enough results to satisfy your intent a lot easier than to produce a paper for a journal.

    I think you'd have a really hard time disproving their conclusion: the lower rolling resistance was great enough to overcome both a power and aerodynamic disadvantage. The biggest problem with their test is how well they maintained the same line, it's possible that on the third attempt they had found a better line. Also the wind could have changed.
    Their conclusion could be made up or simply erroneous. They lack any real credibility, because their tests are not controlled, they don't provide proper evidence either, so as it is, its mere entertainment.

    Despite the cobbled section, pro riders still go faster than 30km/h, so my bet would be the road bike still is the faster option. If we could ask Sagan which bike he would choose for a cobbled section race I'm inclined to think he would choose the road bike as well.

  5. #5
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    Quote Originally Posted by TDLover View Post
    Their conclusion could be made up or simply erroneous. They lack any real credibility, because their tests are not controlled, they don't provide proper evidence either, so as it is, its mere entertainment.
    I agree that it's mostly entertainment but they're not exactly selling it as conclusive science. I don't think their conclusions are made up or erroneous though, they did provide a certain amount of controls and their results somewhat matched.

    The test seemed to be more about tire width than bike styles and it's no surprise to me that a wider tire will be faster and more efficient on rough terrain than a narrow one. Pro riders use significantly wider tires on stages that have less than 10% cobbles, and if the Paris Roubaix were 100% cobbles I'm sure that tires would be much wider than the ones used now.
    I brake for stinkbugs

  6. #6
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    Here's the thing:

    Ride the MTB, and get blown out the back in the first 100km of racing before they even hit the cobbles.

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  7. #7
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    Quote Originally Posted by Le Duke View Post
    Here's the thing:

    Ride the MTB, and get blown out the back in the first 100km of racing before they even hit the cobbles.

    True but the GCN guys weren't arguing otherwise, they came to the same conclusion at the end of the vid.
    I brake for stinkbugs

  8. #8
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    This is coming from a guy who sells only wide road tires, but it seems to be accepted elsewhere. I think CGN pointing out the availability of a better line choice while using the mtb tires is also significant.

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