He doesn't.

25''850 ARNAUD DUBLE (FRA) 10.10.2001 LA PAZ (BOL)

His time is still one of the fastest ever though.

The UCI need to tidy up that page up and update it. The Aussie Teams pursuit record from nearly 18 months ago isn't on there yet!

The spring energy isn't "lost" or otherwise disappears. It's transmitted elsewhere. Where it the question.

Unless you suddenly stopped pedaling or started pedaling backwards, the torque from the spring system is transmitted back to the drive train. The only way it would be "absorbed" would if the leg was not applying enough pressure on the pedal to overcome the torque of the spring system.

That would be true if you kept constant torque all the way around the pedal stroke, but explain what happens at the deap spot.



Although you might be placing downward pressure, the rotational torque of the recreational rider is probably zero, or very close to it at the dead spot, and this is where the built up "spring energy" is lost.

The point of my first post is that the spring system is way, way faster than the cadence of pedaling.

At the deadspot nothing happens because the spring's energy has already been put back into the drivetrain. It doesn't just sit around waiting for the deadspot.

In fact, it the lack of constant torque that allows the spring to rebound during the second half of the power stroke when the torque is decreasing. Once pressure on the pedals starts decreasing immediately after the zenith of the power stroke, the spring's energy starts feeding back. The spring has sprung long before the deadspot.

Yours is a common misconception.

So if I were to use a set of bamboo cranks that really built up some energy, it would have no net effect on the power output to the cranks? If all this energy from flexing were not wasted, then why would all the component manufacturers be so eager to tout stiffness qualities?

Just like with designing a lot of things, it's about compromises. Notice that many bikes use shaped tubings for their bikes? They're shaped for a reason. Round tubes behave similarly in all directions, but shaped tubes might be extra stiff in one direction and flexy in another. For all the parts of the bike that are involved in power transmission, you want them to flex as less as possible. For example, you don't want your BB spindle to be doing a see-saw motion when you're sprinting-->you want that displacement to go toward turning the crank (that's why more and more cranks are going with outboard bearings). Similarly for the front area (if you care about the handling of the bike). You want the bike somewhat flexy when it comes to having shock/vibration transmitted from the road to the rider. It's unlikely you'll see suspensions on road bikes, so you address this issue by trying to address the shock/vibration closes to the source (the parts connecting the wheel to the frame)-->use carbon fiber fork on the front, and things like S-bends on the seat stays, carbon seat stays, etc. So, frame flex is good or bad depending on where it is on the bike.

Yes, but is the reason marketing or engineering? In the case of ti frames, that is not an idle question.

And exactly how many people would pay money for these bamboo contraptions? The purchaser, no matter how engineering challenged, has the final say in design.

Moreover, any point taken to its extreme can be perverted and thereby disproven. My remarks relate to existing, typical bicycles.

* * *

Ironic that you reference Keith Bontrager in your posts. He was one of the first bike personalities to question the received wisdom that frame flex is bad. His article on frame flex, that flex is not necessarily bad, is still floating around the net somewhere, last I checked.

Like these?

http://www.calfeedesign.com/images/bamboo.jpg

Anyway, I still have yet to see anything to convince me that the energy that goes into flexing the frame/drivetrain eventually goes back into it as you continue the pedal stoke.

BTW, if you're going to say "yours is a common misconception", you'd better have something better than your opinion to back it up.

Edit. Never mind.

http://66.102.7.104/search?q=cache:D...ame+flex&hl=en

Cached paged. Bontrager has apparently disowned Keith, except for marketing purposes. There are four previous pages. Anybody got a link to them?

BTY, where's the bamboo crank? And am I understanding you to say that is a typical bike? I was aware of Calfee's bike when I made my earlier statement, hence my use of the term "typical."

-------------->"Anyway, I still have yet to see anything to convince me that the energy that goes into flexing the frame/drivetrain eventually goes back into it as you continue the pedal stoke." <------------- Well I guess that about settles it. You told me, yessiree.

I don't know. I'm pretty comfortable with Keith Bontrager in my corner.

Demonstrate it for youself using paper. Fold them into different shapes. Trying compression, tension, torsion, and bending on the differently shaped paper-folded-tubes. Different shapes will experience the different forces differently-->that's why there will always be compromises in design in terms of stiffness and compliance.

This is a test, repeat a test. It's pass/fail.

Why are there different shaped tubes for Ti bikes but not for steel--generally speaking? (I know some steel bikes have funny shaped tubes, but mostly they don't). There is a very specific reason why steel is round and Ti many times ain't.

You may not want to know the answer if you ride Ti. (Big hint: it has nothing to do with the material's characteristics.)

The engineers here should get this one, easy. And builders are disqualified from participating because it's a no brainer for them.

I knew one day my origami skills would come in handy...... :D

I've an engineering background...but I'm probably stupid...so please enlighten me. :D Hmmm...wonder why they make steel I-beams and not round ones?

There's a lot of ifs and mays in there. It looks more theoretical than factual. At least we agree on one thing: we disagree.

One easy way for a "non lab available" person is to bend a coat hanger back and forth until it breaks. It gets pretty hot, steel aluminum ,whatever. Put your finger on the joint immediately when it breaks, hehehe. There goes the energy you used to bend it as heat. Good-bye it's gone. Get some ice for your finger.
There is friction in things that flex!

Here you go again with all that "reality" stuff ! :)

:beer:

Try and tell someone in Lance's camp that the small energy loss from flex does not matter. Then run!

I like my flexible Ti frame for softening the bumps to my arthritic joints on all my century rides.

Different pedal strokes for different folks.

The histeretic loss factor for steel is in the range of 0.1% to 0.8%. For a traditional steel frame, approximately 1% of total energy per pedal stroke is stored as strain energy in the frame. So at the upper end of histeretic loss for steel 0.8% of 1%, or 0.008%. In a long climb situation this would be a direct 0.008% cost in time, or about 0.3 seconds per hour. In a flat time trial where wind drag is the primary enemy the effect is not as large. We all know that the difference in effort between 19mph and 20mph is much less than 24mph and 25mph. This is because the power required is proportional to the square of the speed. Lance uses about 500W to maintain 50kph. In that case the histeretic cost is about 0.15 seconds per hour. But Lance's bike is carbon fiber which has a higher histeretic loss of around 2%. So the carbon fiber bike has to be 3 or 4 times stiffer just to have the same histeretic loss as a traditional steel bike. If Lance's bike were 10 times as stiff as a traditional steel frame then he would only have an advantage of around 0.07 seconds per hour. But of course his OCLV is not that much stiffer.

Er..no.. the power is proportional to the *cube* of the speed.

I still think most of you are missing the point. A droopy frame transmits vibrations to the rider and energy is dissipated in the body of the rider.

Sorry. You're right. The drag force is proportional to the square of the speed but the power is proportional to the cube of the speed. So in flat terrain the effect of histeretic loss is even less than what I said. The 0.15 seconds per hour should be 0.10 seconds per hour. Anyway the point is the same.

If someone is riding the TDF for a few hours a day for two weeks, it's important. It's the sum of all the small things that add up over a long race.
Thanks for explaining the details, it's very interesting. But I don't think I'm going to get a new frame right now so I can pick up that precious .04 seconds on my all day rides! Maybe I'll just take some lint out of my jersey pockets before I leave the house. That might be more of a difference. :)