Bike Stiffness. How To Tell?
11-09-15, 04:02 PM
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The engineers may wish to weigh-in on the relatedness or lack thereof but it seems to me -- other than the fact that something that is stiff or rigid is less flexible or pliable and vice-versa -- when it comes to the stiffness of a manufactured object, we must also look to the geometry involved. For example, when used as a support beam a wooden 4x2 may be a stiffer than a 2x4.
11-09-15, 04:32 PM
#77
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It is true that stiffness is determined by the amount of force that's required to flex a frame a given distance.
11-09-15, 04:50 PM
#78
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Bike Stiffness. How To Tell?
The stiffness of a frame definitely matters. It's a question of how stiff you want it and where.
BB stiffness enhances energy transfer (at least marginally)
Front end stiffness improves precision in handling, and most importantly inspires confidence in cornering and descending.
At the flexy end I've had frames I could ghost shift by twisting the bob and stays, induce chain rub on the FD and in the worst case throw the chain. You definitely want a frame stiff enough to avoid all those things.
But a bike with stiff seat stays and no vertical compliance will beat you up.
Beauty of all this is bike designers are getting better and better in dialing in the right amount of stiffness where you want it. So a bike, particularly a CF bike can actually be the clichéd laterally stiff and vertically compliant.
BB stiffness enhances energy transfer (at least marginally)
Front end stiffness improves precision in handling, and most importantly inspires confidence in cornering and descending.
At the flexy end I've had frames I could ghost shift by twisting the bob and stays, induce chain rub on the FD and in the worst case throw the chain. You definitely want a frame stiff enough to avoid all those things.
But a bike with stiff seat stays and no vertical compliance will beat you up.
Beauty of all this is bike designers are getting better and better in dialing in the right amount of stiffness where you want it. So a bike, particularly a CF bike can actually be the clichéd laterally stiff and vertically compliant.
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You could get lost and die.
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11-09-15, 05:14 PM
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11-09-15, 05:27 PM
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11-09-15, 05:30 PM
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I don't think anyone bothered to read my earlier post. It explains most of the questions that are being asked here.
But I do find this thread's bro-mechanical engineering quite amusing.
But I do find this thread's bro-mechanical engineering quite amusing.
11-09-15, 05:51 PM
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11-09-15, 05:52 PM
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11-09-15, 05:53 PM
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11-09-15, 05:55 PM
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11-09-15, 05:57 PM
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11-09-15, 05:58 PM
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Interestingly enough, as I understand it, 'stiffness' has to do with how far something can be flexed before it breaks or is permanently deformed because it is no longer able to return to it's original state. So, when you look at it in that way, flexing the frame as the kid did wouldn't cause any permanent deformation because in the range we're talking about, the stiffness of the bike's frame (overall at least and not necessarily at the joints) is more like a compliant rubber band than a stiff and brittle toothpick.
11-09-15, 06:00 PM
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11-09-15, 06:36 PM
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11-19-15, 09:13 AM
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What's funny is the current article tests four steel bikes. The Colnago Arabesque has a total deflection of 7.08mm which was the worse of four steel frames. I saw an older magazine comparing four aero frames. The Fuji Transonic 1.3 which is very stiff per the article had a measurement of 2.15mm.
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