Carbon Frames less efficient?
 

It seems to be generally accepted that carbon is good in forks, handlebars, and seat posts because it adds comfort by absorbing road vibration.
Surely this is basically saying it is damping and absorbing energy?
So why isn't it said that the frame is damping and absorbing the energy the rider is putting through it and is less efficient for transferring power?

It's not quite that simple. The overwhelming majority of vibrations being damped do not contribute in any way to forward motion of the machine. On top of that, the reduction of those same vibrations transferred to the rider correlates to a reduced rider fatigue, increasing rider sustainable power and efficiency.

#laterallystiffverticallycompliant

Yes.

CF frames are usually designed to be pretty stiff with respect to crank forces. Can't lose much to flex when there's not much flex.

The attenuation is frequency dependent.

Road buzz is high frequency with very small amplitude, which CF and resin material attenuate well.

Pedal forces are low frequency, and frame flex is high amplitude (relative to road buzz). CF frame geometry is designed to mitigate this.

OP is right. CF frames are definitely less efficient---sorry, but they are just slower than aluminum and much slower than steel. Even putting raisins in one's oatmeal cannot compensate for the inefficiency of CF.



{OP: please realize my post has nothing to do with you or the very reasonable question you asked ... I am just being a jerk because that is what I do best.**

Hasn't it been established that even a flexy BB area doesn't cost anything significant in overall pedaling efficiency? I recall reading testing data comparing frame materials and how the relative stiffness impacts the force transmitted to the rear wheel. IIRC, this is a dramatic oversimplification but even if a flexy frame "feels" slower to the rider, it has no actual measurable impact on power transmission (talking about a decent steel frame compared to carbon, not a $25 huffy with broken chainstays). It's an elastic sort of flexing where there's no or very little net energy lost due to the nature of the flex.

Of course, I can't find the study I'm talking about so it could be complete nonsense.

Here's an older thread about it-

http://www.bikeforums.net/road-cycli...ood-thing.html

Nothing has been established period. Unless you count the contingent that believes that whatever the pros ride must be best.

It is all in how you design the Mold shape the frame is Built up in Amount, orientation of Carbon cloth
and type used ..

Some frames are faster than others. I've ridden enough bikes to say that's absolutely true. A stiff frame accelerates faster and climbs better. However, once a frame is stiff enough so that I don't flex it noticeably, no matter what, I don't see how stiffer than that would be advantageous for me.

The very cool thing about carbon frames is that their stiffness or compliance can be modified in specific areas. When creating a new frame and/or layup, test riders can take out trial frames and see what they do, both in performance and subjective feel. The layup can be altered and test ridden again. Etc.

Racers ride what's fastest for them unless they have a sponsor contract, and sometimes even then they use rebadged or blacked out frames. There's obviously huge competition between frame manufacturers. If bamboo were faster, that's what would be prevalent in the stores.

Jan Heine has a theory that certain flexy frames are faster because the springyness contributes power to the pedal stroke. He calls it "planing." OTOH he seems to represent a tiny minority advocating flexy frames. I'd go with democracy and market forces on this one. People vote with their dollars. If people really think flexy is faster, there are plenty of old steel frames still out there. They could shock everyone and prove their point at their next road race.

This isn't a thing any more. If a pro team is sponsored by a given bike brand, that's what the rider is on. The only exception seems to be in TT frames, with Villumsen winning the women's TT at worlds last year riding a blacked-out Trek rather than a Willier, which is the sponsor for her UHC team, but that's just because Willier just don't make a frame that can accommodate her ideal TT fit. There's really no performance difference between the major brands in their road bikes any more.

Oh boy, that'll have 'em coming out of the woodwork.

I like to live dangerously.

Oh well if you want to go down that route...

I used to have a Trek 5500 with 9-sp Dura-Ace components, and nice, hand-built wheels.

I also have a Scattante aluminum frame from Perf, onto which I've stuck 9-sp 105 stuff and much cheaper velomax wheels.

I had to ride the Scattante for a bit while my 5500 was getting warranty work done, and my average speed on all my rides was...

...exactly the same as it had been on my 5500.

And I think I paid something like $169 for that Scattante frame w/ fork.

Interestingly enough, there are ZERO studies or any evidence that show that a stiffer bike is faster than a flexy one. Stiffer bikes mainly have the advantage of feeling more stable during sprints. Flex in bikes just return the energy back into the system.

Oh boy, that'll have 'em coming out of the woodwork.

Well, I did use JBWeld and duct tape to get it back together.

Just be sure that these elements are applied in the appropriate orientation - you wouldn't want to mix up your compliance and stiffness.

Yes, I considered that. I'm going to send my daughter out on the bike first.

This makes a lot of sense. Maybe pro sprinters want stiff just because it feels faster? Or allows more focus and concentration?

Hmmm .... Or, when the frame flexes, some of the energy which would have gone to turning the wheel, is lost in the system.

"Back into the system" ... What system? The human power system? The drivetrain? it is sort of like how old muscle cars used to have "axle-tramp" where the engines produced enough torque to wind up the springs and wrap the springs around the axles---so track bars or Lake bars were used to stop the flexing.

I am not a scientist; if you don't like what I say, ignore it. But in every discipline I have ever heard about, flex absorbs energy, dissipates energy ---it is not "returned" anywhere. The energy is used to move something which shouldn't be moving (or doesn't help the vehicle move) and is converted eventually to heat and friction and stretching and bending ... the energy is absorbed by the motion, and is wasted in terms of propulsion.

It takes energy to flex a bike frame--energy which is not moving the bike forward, because the flexion of the frame in no way transfers rotational energy to the rear hub.

Pretty simple example ... would you want to hammer nails all day with a hammer that flexed? When you saw the guy next to you who had a real hammer, driving each nail with X strokes, while you needed X*1.5 blows because your hammer flexed ... any talk about "energy returning to the system" wouldn't make you any less tired. You'd go out and get yourself a hammer which actually transmitted power to the nail.

That's not quite right. Modern technology in the golf industry is all based on energy transfer.(within the rules) Those rules were specifically created to control this energy transfer. I have been out of that sport for about 5 years now, but you need to look there for your answer to how energy is transferred. It is all based on elasticity of the ball and the clubface. The golf ball itself is designed with up to 5 layers, each with a different purpose. The rebound/energy transfer you are speaking of is called "the trampoline effect." Driver faces are specifically designed to maximize this trampoline effect. When hit on the sweet spot, the driver face flexes and deforms at contact, then rebounds. The ball comes off the face with substantial more energy, like jumping on a trampoline.

TRAMPOLINE EFFECT

No, energy is lost in deforming a frame - it is lost in heat.

Energy transfer with a bicycle is pretty simple---the rotating crank transfers energy to the rear wheel and to the ground to propel the bike forward. Any motion which is not in the direction of rotation is not moving the bike forward.

If the shaft of the golf club is not sufficiently rigid, it will flex back from the ball at the moment of impact, wasting energy---imagine a golf club with a thick stiff rope shaft ... not quite going to get those 275-yard drives. If the bottom bracket of a bike flexes side to side, the amount of energy it absorbs---the amount of energy needed to make it bend---is Not getting through the crank arms to the chainring to the chain to the cassette to the ground to propel the bike forward.

Think of it this way---would you wear loose, soft-soled shoes with big thick cushions on the sole when biking? Why not? Because compressing all that cushion and flexing the sole would waste energy---not magically "return energy to the system." The enrgy needed to fully compress all that adding would not drive the bike. The energy absorbed by the bending of the sole would not drive the bike.

Which is why cycling shoes have super-rigid soles ... energy transfer is maximized when flex is minimized.

If you can explain precisely how there is a "trampoline effect" in the bottom bracket of a bicycle frame and how this helps move the bike forward ... I will have learned something. But do consider---- a golf club striking a ball is a direct impact, and the compression and subsequent expansion of the ball is used as a spring to increase distance.

There is no spring in a bicycle's drive train---as with stiff-soled shoes and stiff cranks and a chain which hopefully doesn't stretch, there is no spring. there is no one-time impact, no controlled compression and expansion is response to that impact. The only "impact" as such is the pressure of the feet on the pedals, and there the impact should be continuous force, not a sudden impact.

If there is any compression, it would involve the foot, ankle, and leg---and the idea there is for the foot, ankle and knee to be pushing through the stroke, not springing back ... when your feet, ankles and knees can no longer stop from compressing, when you can no longer extend them to pedal, you have hit max power. The golf ball is supposed to compress and expand---your legs are not supposed to go backwards from the force of pedaling.

Again, consider a very flexy golf club shaft---it might whip on the downswing and snap forward, but if it flexed Backwards or sideways upon impact, you would redesign the club. That would be lost energy.