Carbon fibre

[ncutler]

That you in there, Nick?

LEJOG on it?

I was leaning out of the window in the Cessna with a camera: pilot is Eric, another member of the Gruppe.

LEJOG would be ok

Nick

[andwags]

Wesbrooks - you don't want springyness (is that even a word?) in a bike frame, you want it to deflect and absorb energy - as in your heat example - instead of transferring it to the body, but if you make the frame springy you are losing pedalling efficiency. The best place to add hysteresis is in the tyres - going from 23 mm to 25 mm has a big effect. A good example of this is when you connect a big spring to a small spring: which one will move first? This is the exact reason why a small diameter tubed steel frame is springy compared to a well designed carbon race bike yet the Carbon race bike is just as comfortable with huge perfomance gains.

[WesBrooks]

Wesbrooks - you don't want springyness (is that even a word?) in a bike frame, you want it to deflect and absorb energy - as in your heat example - instead of transferring it to the body, but if you make the frame springy you are losing pedalling efficiency. The best place to add hysteresis is in the tyres - going from 23 mm to 25 mm has a big effect. A good example of this is when you connect a big spring to a small spring: which one will move first? This is the exact reason why a small diameter tubed steel frame is springy compared to a well designed carbon race bike yet the Carbon race bike is just as comfortable with huge perfomance gains.

Better to say stiffness. If your trying to qualify or measure how 'springy' a structure is you'd be looking to measure the spring constant, so long as your system is linear-elastic (ie exert double the force on the structure and it deforms twice as much).

If you have a bike frame deflecting and absorbing energy you will loose pedaling efficiency if it is not specifically designed to damp road vibrations. Absorbing energy means that vibrations are being damped. To damp vibrations the kinetic energy/potential energy in the vibrating frame needs to be either damped by moving air around the frame, or by being converted to heat.

If you only have hysteresis in the tyres and not the frame your rolling losses will be exaggerated as larger tyres means lower pressures giving more tyre deformation, leading to greater losses to rolling resistance. A better option is using frame design that is designed to damp appropriate frequencies to isolate and damp road vibrations, and so not gaining rolling resistance. The only time you would loose pedaling efficiency is is your pedaling frequency approached that of the vibration of the road. Vibration from poor road surface is typically much higher than you pedaling frequency.

I think there is a product out there that does exactly this, I think it's called something like a 'Hertz Damper'.

[reohn2]

'Hertz Damper'.

Thought that was car hire in the rain

[andwags]

I'm afraid you're wrong WesBrooks...

I did mention that carbon frames - good ones anyway - transfer energy into heat rather than flexing.

Also, pro racers have tried the whole building flex into the frame and it made them all slower. Instead they have stiff frames and wider tyres when they hit the cobbles. As my spring example in my last post the tyres are the ones who make more of a difference. You can get a lot more comfort through smaller tyre differences rather than trying to make the frame absorb the bumps.

With Specialized bikes, you're thinking of the Zertz insert which is supposedly there to absorb shock but it doesn't because the frame around it is so stiff, it can't possibly affect the insert. Specialized don't even say it flexes, they say it absorbs vibrations of a certain frequency that has been found to irritate the human body. Truth is - as this is all marketing nonsense - the carbon frame is what is absorbing those irritating frequencies, how else would you explain the excellent ride feels of carbon frames that don't have the silly inserts.

Last note: rolling resistence will decrease if you run a wider tyre at the same pressure as the narrower tyre, because the amount of tyre that is touching the ground shortens and widens. Instead of running a 23 mm tyre on the cobbles at 100 psi, try a 25 mm and you'll be faster.

You simply can't use linear physics in real world applications...

[WesBrooks]

I'm afraid you're wrong WesBrooks...

Read my post very carefully. What I have said is correct. What you have done is read between the lines and understood what I said a different way to what I intended when I wrote it. One thing that I didn't make clear, or should have re-wrote was:

If you have a bike frame vibrating and absorbing energy you will loose pedaling efficiency unless it is specifically designed not to have the harmonic frequencies within sections of the frame matching the frequency of the pedaling.

There is no one ideal bike. For instance, touring road racing, MTB, and time trials all have specific design and engineering challenges to overcome to create an ideal bike for a specific style of riding. Carbon Fibre is a material who's composition can be tailored to suit the specific requirements and the material's manufacturing method imposes less limitations on geometry, and thus allowing the complex designs that are developing in the top end of the many different sports of cycling.

...and your own.

You simply can't use linear physics in real world applications...

Yes you can, you are wrong! You just need to understand the limits of the equation, and what circumstances are likely to cause an error between the real world model and the simulation that will render the results of the simulation invalid. This also applies for non-linear simulations like CFD. No simulation is valid without a degree of qualification by a series of real world tests. If this was not the case wind tunnels would have already been confined to museums.

Last note: rolling resistence will decrease if you run a wider tyre at the same pressure as the narrower tyre, because the amount of tyre that is touching the ground shortens and widens. Instead of running a 23 mm tyre on the cobbles at 100 psi, try a 25 mm and you'll be faster.

A rim will have a maximum pressure that it can withstand for a given tyre size. Generally the smaller the tyre size the greater the pressure. What you have done is introduced complications to illustrate an alternative. Bike design is full of compromises. I could do the same and say; "The 25mm would be heavier, and also slower on the velodrome (I don't have to commute or ride on cobbles so taking it to the super smooth extreme) due to aero losses because of a larger frontal cross section.", or push it past your point "Well put your 25mm tyre on an MTB on the rocks on the down hill of Rivington Peek (a world cup track that was abandond because of too many injuries) and it won't compete with the other similar bike on their larger tyres.".

I've been very careful to make sure what I've said is not mis leading. But there is not one solution for all. Hence why the versatile nature of carbon composite structures is so attractive to bike designers.

[andwags]

What you said makes sense, I was a little hasty with my argument...

As you say, the real world has to qualify the theory of the equation and we all have unique goals so one solution doesn't work for everyone.

Still, Carbon as a bike frame is being used in similar ways for many types of bikes and sometimes getting the bike the best it can be is to rely on the people who take the bikes to the extremes. Riding on cobbles is the harshest thing you can do to a city / commuter / tourer/ racing bike and all those bikes have learnt lessons from the pro racers.

Don't underestimate the importance of your tyres in making your bike perform the way you want it to. Even 2" tyres can be pumped up to 90 psi safely (not the recommended tyre pressure obviously) but fat tyres are just as fast as skinny ones when they're that hard especially when you add bumps into the mix. Obviously, the smoother things become, the closer you get to the lab tests that tell of rolling resistance and that an 18 mm tyre is faster (exactly the same for wind tunnel tests where the 18 mm tyre is deemed the most aerodynamic) put that tyre on the road, pump it to 150 psi and then realise that you've suddenly become slower because every little bump hurts...

[reohn2]

We seem to have wondered off thread and onto tyres.
I agree with andwags,give me comfort on the bike rather than outright speed anytime,I'm currently running 28mm Gators on solo having just changed from 25mm, the comfort factor of the 28mm beats the 25mm handsdown and the bike is just as fast.How people ride 23mm tyres with any degree of comfort beats me especially on the rough tarmac of our roads .

[Robert]

Oh Dear! What did I do?

[andwags]

I don't think we've wondered, it's been a hoot. Discussions always have a degree of evolution...

Now's that would make a good thread... evolution of a topic.

[reohn2]

I don't think we've wondered, it's been a hoot. Discussions always have a degree of evolution...

Now's that would make a good thread... evolution of a topic.

We would have to just let it evolve!

PS what would the title be?as in, where would it start?

[ncutler]

PS what would the title be?as in, where would it start?

In the beginning was The Word

Nick

I'm off to start it .............

Please evolve in: http://forum.ctc.org.uk/viewtopic.php?t=13032

[7_lives_left]

Are carbon fiber components affected by ultraviolet light? I imagine the fibres themselves would be fine, but what about the resin holding the fibres together? I seem to remember that some plastics degrade when exposed to direct sunlight.

[reohn2]

Are carbon fiber components affected by ultraviolet light? I imagine the fibres themselves would be fine, but what about the resin holding the fibres together? I seem to remember that some plastics degrade when exposed to direct sunlight.

Going off the number of plastic bags in the hedgerows round our way they don't degrade fast enough

PS,that maybe coz its not been sunny since last October though!

[Mick F]

I now have 3 bits of CF on Bike. I already had the Campag Chorus rear mech, but I recently fitted Chorus Ergos!

I picked up an absolute bargain of a 2006 NOS set.

The CF makes the brake levers far stiffer than the resin(?)/plastic ones.

I can't say much I like the look, even of the black plastic levers. I would much prefer to have bling .........