devashish_paul wrote:
lyrrad wrote:
I think the biggest effect of frame stiffness can be seen in track sprinting.
Look at videos from times past and the bikes are all over the place under full power.
Look at recent videos and the bikes track remarkably true, almost unbelievably so.
I am sure there are less total losses with a bike that the wheels track each other well.
I also think that flexy steel frames were one of the major reasons that when hill climbing we all seemed to get by on ridiculously high geared bikes in the past compared to the gearing used today.
Also the input amplitude of the vector forces flexing the frame, the degree flex and the period at which said forces apply might be more applicable to the store and release cycle at the longer relative period (and input force) for climbing than the higher input force and smaller period for sprinting...maybe modern carbon frames elastic modulus is more appropriate for sprinting dynamics. Its not that carbon frames don't flex, they do, they just flex in a different way.
Ayup.
If frame flex didn't matter than we all could saw away a chain stay to save weight. If flex was bad then mountain bikes wouldn't have suspension. You can lose power to the ground through flex, you can lose power to the ground through stiffness. Situational what works best where. At minimum being able to point a bike to a specific point and have it end up there is a good thing, but what might produce this end on a track will likely be different on cobbles.
By the way I have a standing "saw the chainstay" offer with a friend about testing his assertion that flex doesn't matter and that any loss is returned. He hasn't taken me up on that in a decade.
Saying you could feel a frame heat up if the flex wasn't returned as power is trolling. There's this thing called dissipation. If you lost 5w into a frame that would amount to a fraction of that heat in any individual place most of which would go bye bye into the airflow around the frame, with a big stack of variables. I'm sure you could develop a very expensive test rig to verify both this and the first law of thermodynamics. I'm thinking "why bother".
Field testing stiffness to efficiency also has a ton of variables. Rider weight, power, surface, frame design, Etc.
Finally, beware taking anything a pro says at face value. They are both paid spokes people, and not necessarily actually knowledgeable about what they speak of. When I was racing motorcycles professionally I would get boxes of product. The boxes would contain stickers, product, a hat, and an envelope. The sticker would go on the bike. The envelope would go into a bank account. The hat on my head. It was hit or miss if the product went into or onto the bike. But it was the best damn product out there, if I wanted to keep the envelopes coming.
Kelly may have been stroking the interviewer, not the frame.
3 Nats titles, 1 Nat record, 17 State champs. 4 wind tunnels. 100's of hours of testing. Still figuring this stuff out.
