Properties of carbon frames

[Membrane]

I'm puzzled by two properties that carbon frames are said to have: more
rigid and more comfortable.

Afaik higher rigidity results in less pedalling power being lost due to
the frame flexing, and a frame is more comfortable when it absorbs
and/or dampens the vibrations that are caused by an uneven road surface.

My (probably flawed) instinct says that these two properties seem
contradictory.

--
Membrane

 

[_]

On Fri, 11 May 2007 09:23:29 +0100, Membrane wrote:

> I'm puzzled by two properties that carbon frames are said to have: more
> rigid and more comfortable.
>
> Afaik higher rigidity results in less pedalling power being lost due to
> the frame flexing, and a frame is more comfortable when it absorbs
> and/or dampens the vibrations that are caused by an uneven road surface.
>
> My (probably flawed) instinct says that these two properties seem
> contradictory.

Advertising has always lied.

I addition, any power loss via frame flex is not determined by rigidity,
but by hystereses.

 

[Jim Higson]

Membrane wrote:

> I'm puzzled by two properties that carbon frames are said to have: more
> rigid and more comfortable.
>
> Afaik higher rigidity results in less pedalling power being lost due to
> the frame flexing, and a frame is more comfortable when it absorbs
> and/or dampens the vibrations that are caused by an uneven road surface.
>
> My (probably flawed) instinct says that these two properties seem
> contradictory.

I think the angle is it absorbs high-frequency vibration caused by the road,
but not the low frequencies (60-100Hz) caused by pedaling.

I think some companies also say they lay the direction of their fibres to
flex one way but not the other.

No idea if any of this is true or not in real use.

 

[Arthur Clune]

Jim Higson wrote:
>
> I think some companies also say they lay the direction of their fibres to
> flex one way but not the other.

Yup. All I can say is that my new carbon bike is lighter, more rigid and
more comfortable than my previous titanium one.

Arthur

--
Arthur Clune PGP/GPG Key: http://www.clune.org/pubkey.txt
The struggle of people against power is the struggle
of memory against forgetting - Milan Kundera

 

[Pete Biggs]

Membrane wrote:
> I'm puzzled by two properties that carbon frames are said to have:
> more rigid and more comfortable.
>
> Afaik higher rigidity results in less pedalling power being lost due
> to the frame flexing, and a frame is more comfortable when it absorbs
> and/or dampens the vibrations that are caused by an uneven road
> surface.
>
> My (probably flawed) instinct says that these two properties seem
> contradictory.

There wouldn't be a condradiction if the frame was laterally stiff but
vertically compliant.

I don't know if any non-suspension frames /really/ provide that, or if it's
all in the mind.

~PB

 

[Nick Maclaren]

In article <[email protected]>,
"Pete Biggs" <[email protected]> writes:
|> Membrane wrote:
|> > I'm puzzled by two properties that carbon frames are said to have:
|> > more rigid and more comfortable.
|>
|> There wouldn't be a condradiction if the frame was laterally stiff but
|> vertically compliant.

In which case it would bounce like a pogo-stick.

|> I don't know if any non-suspension frames /really/ provide that, or if it's
|> all in the mind.

At best. The ghastly F.W. Evans bicycle I bought flexed because that
was dogma at the time, which meant that it slipped a gear every time
I put my foot down hard on the pedals.


Regards,
Nick Maclaren.

 

[Phil Cook]

Nick Maclaren wrote:

>
>In article <[email protected]>,
>"Pete Biggs" <[email protected]> writes:
>|> Membrane wrote:
>|> > I'm puzzled by two properties that carbon frames are said to have:
>|> > more rigid and more comfortable.
>|>
>|> There wouldn't be a condradiction if the frame was laterally stiff but
>|> vertically compliant.
>
>In which case it would bounce like a pogo-stick.

Only if you ignore the damping.
>
>|> I don't know if any non-suspension frames /really/ provide that, or if it's
>|> all in the mind.
>
>At best. The ghastly F.W. Evans bicycle I bought flexed because that
>was dogma at the time, which meant that it slipped a gear every time
>I put my foot down hard on the pedals.

Perhaps you need to develop a more fluid pedaling style. Flexible
frames are more suited to spinners than mashers
--
Phil Cook looking north over the park to the "Westminster Gasworks"

 

[Nick Maclaren]

In article <[email protected]>,
Phil Cook <[email protected]> writes:
|>
|> >|> > I'm puzzled by two properties that carbon frames are said to have:
|> >|> > more rigid and more comfortable.
|> >|>
|> >|> There wouldn't be a condradiction if the frame was laterally stiff but
|> >|> vertically compliant.
|> >
|> >In which case it would bounce like a pogo-stick.
|>
|> Only if you ignore the damping.

In which case, it would lead to energy loss! While, in THEORY, you can
have flexing, damping and minimal energy loss together, in practice
that doesn't happen.

|> >|> I don't know if any non-suspension frames /really/ provide that, or if it's
|> >|> all in the mind.
|> >
|> >At best. The ghastly F.W. Evans bicycle I bought flexed because that
|> >was dogma at the time, which meant that it slipped a gear every time
|> >I put my foot down hard on the pedals.
|>
|> Perhaps you need to develop a more fluid pedaling style. Flexible
|> frames are more suited to spinners than mashers

Why should I fit myself to a bicycle rather than the converse?

I was sold a bicycle that was unsuitable for the purpose for which I
bought it. Leave it at that. At the time, I didn't know 5% of what
I discovered later (partly because of that experience) about bicycle
engineering.

Since then, the "flex is good" dogma has been replaced by "rigidity
is good", which at least has some engineering justification.


Regards,
Nick Maclaren.

 

[Pete Biggs]

Nick Maclaren wrote:

>>>>>> There wouldn't be a condradiction if the frame was laterally
>>>>>> stiff but vertically compliant.
>>>>
>>>> In which case it would bounce like a pogo-stick.
>>>
>>> Only if you ignore the damping.
>
> In which case, it would lead to energy loss! While, in THEORY, you
> can have flexing, damping and minimal energy loss together, in
> practice that doesn't happen.

Perhaps the cyclist being more comfortable makes him more efficient overall
despite the particular energy loss from the frame.

What about motocycle suspension? There must be some energy loss involved,
but overall effiency is greater because the bike has better traction, etc.

I'm skeptical about the supposed vertical flex of steel and titanium "rigid"
bicycle frames, but perhaps there really is a useful amount with a good
carbon one? I don't know.

A frame could be built stiff around the bottom bracket for lateral rigidity,
but have more flexible stays for some vertical movement. I think it's just
a question of how much. Are we talking fractions of a mm, a couple of mm,
or several mm?

~PB

 

[Ian Smith]

On 11 May 2007 10:46:10 GMT, Nick Maclaren <[email protected]> wrote:
>
> In article <[email protected]>,
> "Pete Biggs" <[email protected]> writes:
> |> Membrane wrote:
> |> > I'm puzzled by two properties that carbon frames are said to have:
> |> > more rigid and more comfortable.
> |>
> |> There wouldn't be a condradiction if the frame was laterally stiff but
> |> vertically compliant.
>
> In which case it would bounce like a pogo-stick.

Only if it was as vertically compliant as a pogo-stick. If it were as
vertically compliant as (say) a brick, it would bounce like a brick.

Why do you assume that if anything is vertically compliant it must be
as vertically compliant as a pogo-stick?

regards, Ian SMith
--
|\ /| no .sig
|o o|
|/ \|

 

[Tony Raven]

Pete Biggs wrote on 11/05/2007 10:57 +0100:
> Membrane wrote:
>> I'm puzzled by two properties that carbon frames are said to have:
>> more rigid and more comfortable.
>>
>> Afaik higher rigidity results in less pedalling power being lost due
>> to the frame flexing, and a frame is more comfortable when it absorbs
>> and/or dampens the vibrations that are caused by an uneven road
>> surface.
>>
>> My (probably flawed) instinct says that these two properties seem
>> contradictory.
>
> There wouldn't be a condradiction if the frame was laterally stiff but
> vertically compliant.
>
> I don't know if any non-suspension frames /really/ provide that, or if it's
> all in the mind.
>

As Jobst, Sheldon and others have pointed out, any vertical compliance
in the frame is dwarfed by the vertical compliance in the tyres. Most
of the difference people sense is either different tyres and pressures
or in the mind.

--
Tony

"The most savage controversies are those about matters as to which there
is no good evidence either way."
- Bertrand Russell

 

[Simon Mason]

"Arthur Clune" <[email protected]> wrote in message
news:[email protected]...
> Jim Higson wrote:
>>
>> I think some companies also say they lay the direction of their fibres to
>> flex one way but not the other.
>
> Yup. All I can say is that my new carbon bike is lighter, more rigid and
> more comfortable than my previous titanium one.
>

Mine's not more comfortable as it's a TT bike which is a pig to ride ;-)

--
Simon Mason
http://www.simonmason.karoo.net

 

[Simon Brooke]

in message <[email protected]>, Membrane
('[email protected]') wrote:

> I'm puzzled by two properties that carbon frames are said to have: more
> rigid and more comfortable.
>
> Afaik higher rigidity results in less pedalling power being lost due to
> the frame flexing, and a frame is more comfortable when it absorbs
> and/or dampens the vibrations that are caused by an uneven road surface.
>
> My (probably flawed) instinct says that these two properties seem
> contradictory.

Maybe. I think with carbon it's a lot easier to put the stiffness where you
want it. If you want a component to be stiff in one dimension but flexible
in another, or stiffer at one end than the other. with carbon that's easy
to engineer.

I ride a carbon bike and love it. You get far less 'buzz' - less road
vibration. Carbon (or at least my bike) seems exceedingly good at damping
that out. At the same time the area round the bottom bracket is massively
beefed up compared to a metal frame, and it really does not flex at all.

--
[email protected] (Simon Brooke) http://www.jasmine.org.uk/~simon/

;; 99% of browsers can't run ActiveX controls. Unfortunately
;; 99% of users are using the 1% of browsers that can...
[seen on /. 08:04:02]

 

[Membrane]

Simon Brooke <[email protected]> wrote:

>I ride a carbon bike and love it. You get far less 'buzz' - less road
>vibration. Carbon (or at least my bike) seems exceedingly good at damping
>that out.

The reason I asked is that second hand carbon frame bikes are beginning
to come into reach of my budget, e.g. there was recently a Specialized
S-WORKS Tarmac with a Campagnolo Carbon Record group set for < £500.

One thing I'd be concerned about is breaking something made out of
carbon, the cost of new carbon parts could be prohibitive. I do most of
my own maintenance and I don't have or use a torque wrench. I've built
up an instinct for the limits of the various metals, not so for carbon.
How fragile is carbon?

--
Membrane

 

[Pete Biggs]

Membrane wrote:

> The reason I asked is that second hand carbon frame bikes are
> beginning to come into reach of my budget, e.g. there was recently a
> Specialized S-WORKS Tarmac with a Campagnolo Carbon Record group set
> for < £500.
>
> One thing I'd be concerned about is breaking something made out of
> carbon, the cost of new carbon parts could be prohibitive. I do most
> of my own maintenance and I don't have or use a torque wrench. I've
> built up an instinct for the limits of the various metals, not so for
> carbon. How fragile is carbon?

It's crushable. But you won't be screwing directly into carbon, rarely be
clamping it, so there isn't a lot of difference in that way.

For examples, the carbon Ergo levers have metal handlebar bands and the same
bodies as the non-carbon levers, carbon cranks have metal inserts for the
pedals, the derailleurs are still mostly metal. Forks only need to be
clamped firmly enough to prevent the stem rotating.

So don't worry about the components. The frame, on the other hand, I don't
know, I'd be worried about loosing all that money in a crash.

~PB

 

[Membrane]

"Pete Biggs" <[email protected]> wrote:

>carbon cranks have metal inserts for the
>pedals

I'd be worried to break the bond between the metal inserts and the
carbon.

>So don't worry about the components. The frame, on the other hand, I don't
>know, I'd be worried about loosing all that money in a crash.

I've thought about that too. My fear may be skewed due to seeing body
parts on F1 cars shattering on impact. Afaik F1 carbon body parts are
explicitly engineered to absorbs energy by shattering, I don't know how
impact resistant carbon bike frames are.

But I wouldn't trust an aluminium frame with a simple dent in it anymore
either.

--
Membrane

 

[Simon Brooke]

in message <[email protected]>, Pete Biggs
('[email protected]') wrote:

> Membrane wrote:
>
>> The reason I asked is that second hand carbon frame bikes are
>> beginning to come into reach of my budget, e.g. there was recently a
>> Specialized S-WORKS Tarmac with a Campagnolo Carbon Record group set
>> for < £500.
>>
>> One thing I'd be concerned about is breaking something made out of
>> carbon, the cost of new carbon parts could be prohibitive. I do most
>> of my own maintenance and I don't have or use a torque wrench. I've
>> built up an instinct for the limits of the various metals, not so for
>> carbon. How fragile is carbon?
>
> It's crushable. But you won't be screwing directly into carbon, rarely
> be clamping it, so there isn't a lot of difference in that way.
>
> For examples, the carbon Ergo levers have metal handlebar bands and the
> same bodies as the non-carbon levers, carbon cranks have metal inserts
> for the
> pedals, the derailleurs are still mostly metal. Forks only need to be
> clamped firmly enough to prevent the stem rotating.
>
> So don't worry about the components. The frame, on the other hand, I
> don't know, I'd be worried about loosing all that money in a crash.

When I crashed mine, it got sent back to Dolan's for inspection, and they
passed it as good. I replaced the forks and handlebars on the
precautionary principle, although neither showed any visible damage. It
was all back and reassembled before I was out of the brace...

If you buy a LOOK frame, it comes with an individual statement of its
original (at manufacture) stress test values. If it's crashed it can be
put back on the stress test rig and retested; if it comes out out within a
specified percentage of its original values it gets passed as good. Other
makes may do the same thing these days, I don't know.

Obviously the problems with carbon include

* Structural damage may not be visible on the surface
* Structural damage generally isn't repairable
* If it does break, you can get some very nasty sharp edged bits

But against that, it's incredibly strong. In my crash, my front wheel hit a
boulder weighing several tons while travelling at 46mph. As I say we
replaced the forks just to be careful, but you honestly could not tell
that they'd been in a crash. They looked like new. I don't believe any
metal forks would have survived nearly so well.

--
[email protected] (Simon Brooke) http://www.jasmine.org.uk/~simon/

Wise man with foot in mouth use opportunity to clean toes.
;; the Worlock

 

[Adam Lea]

"Simon Brooke" <[email protected]> wrote in message
news:[email protected]...
> But against that, it's incredibly strong. In my crash, my front wheel hit
> a
> boulder weighing several tons while travelling at 46mph. As I say we
> replaced the forks just to be careful, but you honestly could not tell
> that they'd been in a crash. They looked like new. I don't believe any
> metal forks would have survived nearly so well.
>

Wow. You are fortunate to be still alive. Was it a boulder that had fallen
down a hillside into the road? What injuries did you sustain?

 

[Pete Biggs]

Membrane wrote:
> "Pete Biggs" <[email protected]>
> wrote:
>
>> carbon cranks have metal inserts for the
>> pedals
>
> I'd be worried to break the bond between the metal inserts and the
> carbon.

Pedals don't have to be fitted terribly tightly on istallation anyway
because the precession effect stops them unscrewing in use. I don't know
how good those bonds are in the long run, though.

>> So don't worry about the components. The frame, on the other hand,
>> I don't know, I'd be worried about loosing all that money in a crash.
>
> I've thought about that too. My fear may be skewed due to seeing body
> parts on F1 cars shattering on impact. Afaik F1 carbon body parts are
> explicitly engineered to absorbs energy by shattering, I don't know
> how impact resistant carbon bike frames are.
>
> But I wouldn't trust an aluminium frame with a simple dent in it
> anymore either.

It's not just that I'd be worried the carbon frame was more fragile and
prone to failure without warning (if it is?), it's the replacement cost if
anything did happen. I know from experience that even a relatively strong
steel frame can be ruined in a moment of inattention. (Getting hit by a
motorycle, in my case).

Owning an expensive groupset isn't so worrying in this way -- because the
whole lot is not going to be destroyed in one go (and no one part of it is
as expensive as a carbon frame) -- unless you get run over by an HGV, in
which case you wouldn't care because your brain would be squashed flat along
with the bike

~PB

 

[Simon Brooke]

in message <[email protected]>, Adam Lea
('[email protected]') wrote:

>
> "Simon Brooke" <[email protected]> wrote in message
> news:[email protected]...
>> But against that, it's incredibly strong. In my crash, my front wheel
>> hit a
>> boulder weighing several tons while travelling at 46mph. As I say we
>> replaced the forks just to be careful, but you honestly could not tell
>> that they'd been in a crash. They looked like new. I don't believe any
>> metal forks would have survived nearly so well.
>
> Wow. You are fortunate to be still alive. Was it a boulder that had
> fallen down a hillside into the road? What injuries did you sustain?

No, it was an idiot descending a hill on a road he didn't know on his
tribars, and completely overcooking the bend. I went off the road, hit the
boulders, broke my back. I then got back on the bike and rode another mile
before admitting I was hurting too much to continue. It was my fiftieth
birthday, and I have to say that is NOT a good way to celebrate!

--
[email protected] (Simon Brooke) http://www.jasmine.org.uk/~simon/

;; may contain traces of nuts, bolts or washers.