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Being a car guy and autocrosser, I'm familiar with suspension systems and the necessity to find a balanced spring/shock combination to create the best possible compliance, ride quality and performance in the suspension.

So I can't help but think that the Isospeed technology on the new Trek Domane is a little odd as it's essentially all spring and no damper. Aren't you going to essentially have undamped motion while riding? For example, you can see the bounce in this video...

I haven't ridden one of these bikes yet, but I'm not sure if a short test ride would be enough to make a proper assessment.

And I know this isn't exactly a conventional spring. So I suppose my question is if there's anything about Isospeed that gives it some sort of damping characteristics to minimize excessive bounce?

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4 Answers

up vote 3 down vote accepted

As you already suggest the behaviour is not that of a conventional spring. Compared to a conventional spring I would expect it to have some quite high internal damping so it may have characteristics similar to a spring/shock combination.

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I did a bit of research about carbon fiber and one of the things that many sources cite as an advantage is its vibration damping. What I'd love to find is a comparison of a steel spring to a carbon fiber spring and the internal damping of each. But no such luck. I have a feeling the material is a key part of this design though. –  Steve Wortham Oct 24 '12 at 19:12
    
I don't know how you did your search, but as the carbon stem of the bike behaves more or less like a leaf spring maybe you would find some more information if you narrowed your search to something like that. –  Benedikt Bauer Oct 24 '12 at 19:24
    
It seems to me that carbon fiber is used to manufacture archery bows, and a blade of carbon fiber feels very springy when flexed by hand, indeed. –  heltonbiker Oct 24 '12 at 19:47
    
@SteveWortham I think a lot of texts refer to "vibration damping" of materials meaning impact reduction by pure elastic action, even with no actual viscous damping. –  heltonbiker Oct 24 '12 at 19:48
    
@BenediktBauer - Good call on the leaf springs. I found something (I posted an answer below). I still couldn't find any hard numbers, but that's OK. –  Steve Wortham Oct 24 '12 at 21:02
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I just found this from a carbon fiber leaf spring manufacturer...

In comparison with steel leaf springs they have significantly greater spring action, higher internal damping and a more balanced springing behaviour, with a many times greater retention capacity of elastic energy than spring steel.

http://www.prause-durotec.de/index.php?option=com_content&view=article&id=52&Itemid=59&lang=en

I don't know how much of an influence this internal damping of carbon fiber really has. But it does make more sense to me now. I can see how the Domane could work well.

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I'd be willing to bet that whatever characteristics Trek gave that frame, those are exactly the characteristics that Trek wanted the bike to have. That man appears to be flexing the frame as hard as he can to get it to bounce. A video of a guy on a trainer isn't going to reveal much of anything useful in the real world. If you want to know how the bike does, you really do have to take it for your own test drive.

I'd take the bouncing motion in the video with a grain of salt. The Domane is said to be very well designed and road worthy.

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Motion is not always bad. I'd say with conventional bike the body moves the same way, at the cost of perineal soft tissue and ischial bones crunching aganist the saddle... –  heltonbiker Oct 24 '12 at 18:25
    
Well yes, exactly, the Domane is designed to give you some extra comfort by absorbing some of those vibrations. Though, I think you've got to get yourself a better saddle if you're perineal tissue is crunching against it. –  hillsons Oct 24 '12 at 21:27
    
I see it, but the crunching is due to the road, not the saddle. A proper saddle to ride cobblestones with skinny-hard-as-a-rock tires should be cushioned or mounted on a suspension post. That's the very reason to concentrate shock-absorption in the frame, allowing the bike and its components to remain lightweight, I think. –  heltonbiker Oct 24 '12 at 22:37
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I'd say the rider is the damper, since that few milimeters of travel can easily be "swallowed" by rider's action/body after he got used to it.

(I ride very rough streets with an old steel road bike, and for sure, based on what rough streets feel like to me while on the bike, I would love to ride a bike behaving as the one shown in this video.)

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