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[quote=cynic-al ]I thought it was obvious...so that was on a round tubed steel frame?
Will the flattened top tubes on modern alu frames be the same
Sorry, it wasn't as I'd dismissed it way before doing the full frame calcs - apologies for not making that clear. We're still talking about seat tube flex? I shouldn't think the shape of the top tube makes a huge amount of difference to that, simply how much material there is in it as that's mostly just under compressive load (there is some bending, but not very much and that's pretty much all right at the headtube where it doesn't affect seat tube bending).
Ah, so you don't think "vibration energy can be dissipated without actual flex" you're simply arguing about how much flex there has to be?
Well not quite - we haven't really defined flex, but I'd take that to mean the tubes bending perpendicular to their length. That's not necessary to dissipate vibrational energy. I'd guess that the tubes of a frame are vibrating in every which way, longitudinally and laterally, and that this energy is being absorbed differently in different materials, regardless of *lateral* flex which is what you're talking about.
5mm of vibration
Which there would never be in a real life situation which is what I'm talking about.
Or to look at it another way, check out the materials typically used for vibration damping purposes.
Red herring. Totally different situation. Carbon fibre, steel, titanium and aluminium are never used for vibration damping, but that doesn't mean that they transmit vibrations perfectly, nor does it mean they all do it the same.
My point is (despite all this bickering) that just because you don't measure lateral flex in tubes, doesn't mean vibration energy isn't being lost.
[quote=DanW ]They find the same things with the same assumptions as you.
That does at least show that none of us is missing anything obvious, and I'd hope most people at least trust MB's knowledge more than they might mine.
The bike doesn't sit bolt upright all the time and just by virtue of being able to feel a BB twist under load tells you there are forces acting in other directions.... how about sprinting with the bike being tossed from side to side, cornering, even normal pedaling will have some degree of movement in other directions which influences efficiency, handling and comfort
Sure they might, but I don't think I've ever seen anybody suggest "this bike is really comfy when I'm pedalling, but so harsh when I'm coasting", which tends to suggest that human perception isn't identifying any effects on comfort due to pedalling. Let me just put the cornering one to bed though - when you're cornering the force is still straight down through the vertical plane of the frame, if it wasn't you'd fall off.
[quote=molgrips ]
5mm of vibration
Which there would never be in a real life situation which is what I'm talking about.
...
My point is (despite all this bickering) that just because you don't measure lateral flex in tubes, doesn't mean vibration energy isn't being lost.
I'm sure there is vibrational energy being lost. But to come back to the real life situation, if there is only 1mm of vibration being damped in the frame then that's not enough for any noticeable difference in the comfort of the frame given the other bits between you and the road which will damp a lot more than that. The whole point here is that if you looked at the frames in isolation there might well be significant differences, but frames aren't used in isolation and any flex or vibration damping they provide is dwarfed by the other bits. In the context of vibration damping, given how much flex you can calculate there is, it's not unreasonable to model them as being infinitely stiff.
BTW I'm hoping this isn't all just bickering - I'm doing my best to explain my points and have a proper discussion.
I don't actually give a shit why it is. I'm still grappling with the notion that a superlight ti frame is no different comfort wise to my old OCLV road bike, which was hideously harsh. A lot of people imagined that, very odd.
if there is only 1mm of vibration being damped in the frame
I'm not sure I'd measure vibration damping in mm.. more like attenuation vs frequency... I don't think we're talking about the same thing.
Having a frame flex might absorb *hits* but that's not the same thing as vibration damping. A van's suspension absorbs many cm of road bumps but the panels still vibrate and make a lot of noise. To quieten that down you stick dynamat on the inside - the panels still flex when you push them, and the suspension still works the same, but the noise is far less. Vibration damped.
I'm saying that a carbon frame or whatever won't absorb road hits any differently to an alu one for the reasons you say, but the hits could easily *feel* different....
Have to say I'm with njee...
[quote=molgrips ]I'm not sure I'd measure vibration damping in mm.. more like attenuation vs frequency... I don't think we're talking about the same thing.
It's just different ways of measuring it. The 1mm is the vibration amplitude, not the vibration damping. If you want to measure it as a wave, then that is a pretty valid way to measure P-P for a physical wave - in the same way you'd measure P-P in V for an electrical wave, which would directly translate to dBmW given the electrical impedance (for the vibration in the frame you'd need to know the stiffness of the tube to convert to an equivalent dBmJ figure - in this case the wave has energy rather than power). I'm hoping you're following me here - you've done engineering?
In the case of your van panels we are talking a totally different order of magnitude of flex involved. Not only that, but I suspect you'd find if you attached a saddle to them and sat on it that would do a pretty good job of damping the vibrations.
Yes of course but I was giving examples of how small vibrations behave differently to big hits. In your frame flex experiment, where you statically load a frame, you're not testing the same thing as the riders are reporting.
You're basically saying that there's no difference in comfort between frame materials - and other riders are saying there is?
Back to aero...
http://www.met-helmets.com/index.php?option=com_content&view=article&id=255
http://road.cc/content/news/158211-met-manta-aero-helmet-launched-tour-de-france
Liking the look of these, as good looking as the Evade without the specialness of the Air Attack. Wonder when it'll be available?
Lolz @ the 10W at 50km/h 😆
Why not? Evade claimed @ 20W over Prevail
Aimed at the 50km/h!
I've got a Cervelo S3, because it's red
Ah I see. I too bemoaned Scott for using 45kph recently.
Looking into it I saw cdas quoted for the various helmets. Folk seemed to forget that non aero ones have a larger frontal area , which must also increase with size.
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I'll just leave this here then
Errr, good resurrection there.