Carbon rip off (vs Aluminium)

[MAESTRO's]

Got no messages.

 

 

Daemon,

 

tried to PM you again.....no luck.

 

 

[Johan Bornman]

People have different opinions' date=' and not everyone will agree with you...that's life get over it.
The steel lemond is a smooth ride...some carbon frames do absord vibrations more for me....but frankly, I don't care what you think, it's about what works best for me as a cyclist, and so far a carbon frames makes me feel less tired on rougher surfaces and I love the smooth feel of the lemond frame, and my little alu frame flexes all over the place, but still feels rougher on bad surfaces than the carbon frame, that's sooo much stiffer.

[/quote']

 

You read me wrong. I have no problem with opinion, unless it is first presented as fact, and then later claimed to have been opinion. Have a look around you, even in this thread. People start off with a statement and as it goes pear-shaped, they fall back on their constitutional right to express opinion. Very seldom does somebody say "Oh, I see what you mean..."

 

But, whilst opinion is perfectly legit, in physics there is very little room for it. This is the tech forum where opinion should rather be backed up by some solid observations and science.

 

Lets keep this discussion on the straight and narrow.

 

[Johan Bornman]

The only way to resolve this debate is to measure. (Dilbert is looking very happy ) It will take some accelerometers' date=' a modal hammer, a signal amplifier & some vibration analysis software, & some frames to measure. Oh yes, some money to pay for using the equipment, & some tough bouncers to hold all the unhappy bike companies at bay.

 

pic of the Cervelo R3, with very thin seatstays:

http://www.cervelo.com/models/2008/thumbnail/2008-R3.png

[/quote']

 

Naaah, we don't need all that stuff, although I can do with some bouncers from the guys here who want to moer me.

 

I know from some finite element analysis done on wheels, that a person hitting a bump the size of an average speed hump in a parking yard, causes a downward force on the bike of about four times the person's mass. The speed is something like 25 kph.

 

Therefore we take that Cervelo frame, restrain it so that the chainstays are off the ground and load it with 4 x 80kgs and measure the deflection in the seatstays and of course the vertical deflection along a plumb line hung from the seat collar.

 

My guess is we'll see ziltch. Those chainstays are just too beefy and the deflection we're looking for, whereby the seatstays bow out, will just not happen.  Although the seatstays are very thin, they won't buckle (Euler's bucking for those that care) because they are relatively short,their ends are fixed and the cantilevered chainstays are oversized.

 

 

I also guess that the most compliance on that bike will be in the seat post that will flex backwards as you hit that bump.

 

If Cervelo claimed that these seatstays flex and therefore offered compliance, they're just talking marketing physics, something completely different from physics.

 

 

 

 

Johan Bornman2007-11-19 07:23:49

[dirtrider]

That is why I got all those shocks on my bike ! Carbon sucks ! Ok now I have also added a lot of value to this topic .

[greatwhite]

Several of you disagree with me' date=' but I suggest you guys come up with a unified story in order not to contradict yourselves.

To quote one post: "A good example of this would be to take a tube and smack it on a square edge. Unlike a steel, titanium or aluminum tube that would ring through your hand, the vibration in the carbon tube is deadened. "

 

To quote another post: "Yup friend of mine got a old steel Lemond frame....what a pleasure to ride, sooooooooo smooth".

 

How does this work?

[/quote']

 

Johan - you set yourself up for it, mate. I'm guessing you are (like me) a mechanical engineer and you suffer from "I don't tolerate BS" desease (like me too - and the reason I started this post).

 

The problem is when people have been indoctinated by those sneaky (and sometimes outright lying) marketing folks, bought the product and enjoyed it, they don't like to be told that they were just suckered out of 10k when 3k would have bought a frame just as light but with welds instead of a fancy weave.

 

Personally I agree with many (but not all) of the comments you make, but you're fighting peoples emotions and logic ends up not carrying too much weight in those situations.

 

(BTW the cervelo has a deadstraight seat stays, unlike the 'dale, so I'm at a loss as to the mechanism used for damping)

 

 

greatwhite2007-11-19 05:31:09

[shadowchaser-d]

Several of you disagree with me' date=' but I suggest you guys come up with a unified story in order not to contradict yourselves.

To quote one post: "A good example of this would be to take a tube and smack it on a square edge. Unlike a steel, titanium or aluminum tube that would ring through your hand, the vibration in the carbon tube is deadened. "

 

To quote another post: "Yup friend of mine got a old steel Lemond frame....what a pleasure to ride, sooooooooo smooth".

 

How does this work?

[/quote']

 

Johan - you set yourself up for it, mate. I'm guessing you are (like me) a mechanical engineer and you suffer from "I don't tolerate BS" desease (like me too - and the reason I started this post).

 

The problem is when people have been indoctinated my those sneaky (and sometimes outright lying) marketing folks, bought the product and enjoyed it, they don't like to be told that they were just suckered out of 10k when 3k would have bought a frame just as light but with welds instead of a fancy weave.

 

Personally I agree with many (but not all) of the comments you make, but you're fighting peoples emotions and logic ends up not carrying too much weight in those situations.

 

(BTW the cervelo has a deadstraight seat stays, unlike the 'dale, so I'm at a loss as to the mechanism used for damping)

 

 

I think you hit the nail on the head!!!

 

I really enjoy Johan posts, he always seems to ruffle feathers!  Not a tech junkie myself, once having read what he has to say, more often than not it is all quite truthfull.

[Christie]

Spot on, greatwhite. I think it is great that people have different opinions, as long as a) marketers are not seen as experts b) foreign people seen as smarter than Saffas c) we stay civilized

 

about the damping mechanism: To get structural damping, you need elastic stress. More vertical deflection means more elastic stress, giving more structural damping. It looks as if the R3 structure was designed to allow more vertical deflection at the rear dropout. As JB pointed out, it is debatable as to how effective it would be, and also, the energy lost to structural damping is very very small, so while it can me measured in a lab,  can a rider feel the difference, and if so, what is he feeling - perhaps just an acoustic effect?

[greatwhite]

Spot on' date=' greatwhite. I think it is great that people have different opinions, as long as a) marketers are not seen as experts b) foreign people seen as smarter than Saffas c) we stay civilized

 

about the damping mechanism: To get structural damping, you need elastic stress. More vertical deflection means more elastic stress, giving more structural damping. It looks as if the R3 structure was designed to allow more vertical deflection at the rear dropout. As JB pointed out, it is debatable as to how effective it would be, and also, the energy lost to structural damping is very very small, so while it can me measured in a lab,  can a rider feel the difference, and if so, what is he feeling - perhaps just an acoustic effect?

[/quote']

 

Those seat stays are so thin, I was asking myself about their purpose - almost a case of "they are intended to flex" as a reslt of their slenderness ratio?. Certainly, meaningful axial compression of any useful magnitude would seem unlikey. If they were intended to flex, why not incorporate a slight curve to induce a controlled compliance. Certainly the large vertical section of the chain stay suggests it is supposed to be vertcally stiffer than the average chain stay (someone mentioned that earlier, I think), so seatstays deal with reduced load, but without a giving a great amount of thought, I don't see this making the back end of the frame any 'softer' (vertically)

[Johan Bornman]

cut cut cut...... and if so' date=' what is he feeling - perhaps just an acoustic effect?[/quote']

 

May I embelish on that a little.... I want to go as far as remove the "feel" from your sentence and suggest that he is feeling nothing, but hearing something, hence my original use of "acoustic". 

 

Back in the early days of carbon fibre bikes, Kestrel made some or other revolutionary bike that looked something like a black tupperware guitar. You could hear this thing coming at you from three peletons back. It made an awful racket, yet when I took it for a spin, I couldn't feel anything out of the ordinary. Now If I wanted to, I could have attached all sorts of "feeling" that could match the sound, however, I am at lost for words, the sound was just too strange.

 

 

[lowracer]

ok, if you buy a new car, will you trust the 1950's salesman if he kicks the tyres? or do yourself take the vehicle for a drive and see how it handles around the corners?

for the engineers here : how much does a aliminum bicycle deflect during normal use. or if you take just a seat tube, not the complete bike. if you put one end in a bench vice and can deflect one end 0.5 centimeter, how long (for how many cycles) will the piece last? hmm, not really that long ...

 

in a triangulated frame, you wont even get that much deflection.

 

which begs the question, wil you be able to feel 0.5 cm deflection?

 

If you have 3 exactly the same bikes, the same geometry, the same setup, and painted so that you cannot see what is is made of ... you wont feel the difference.

 

what does affect the ride quality?

the tyre pressure, diameter of the tyre (think 19mm, 21mm, 23mm, 25mm, etc)

The diameter of the wheel

the geometry of the bike (all the angles of the frame, length of the tubes)

The bb height

the stem length

the width of the handlebars.

the trail of the fork.

the wheelbase

 

you go and change the fork of a racing bike to a touring bike or tandem fork, and it will make more difference than the frame material.

 

on a racer how much difference does a 19mm compared to a 25mm tyre make. (or a 1in vs 1.75 in slick on a mtb. heck, play around with the tyre pressure)

 

you cannot compare 2 bikes of different frame materials in terms of ride quality, if everything else is not the same.

 

 

 

 

 

 

 

 

[RockCoach]

 

 

Agreed on the comment about denting ali vs snapping carbon - was going to say that in my original post' date=' but figured I'd said enough already.

 

As for fatigue life, I'm a big lad and I work on 3 years for a frame - if it hasn't broken by then, I'm very pleased - all failures happen in the BB area:

In the case of my early steel frames, it would appear crystaline break down of the manganese molybdenem steel alloy (Reynolds tubes) due to over temp during brazing might have been contributory in some cases, but the failures we typical cyclic fatigue failures

My titanium pinarello failed at the bottom of the front deraileur hanger, again typical high cycle fatigue. I suspect the crack propogated from a tiny weld notch but could never find it.

Aluminium frames will always fail eventually given aluminiums lack of a cyclic fatigue limit - my experience bears this out.

I've never broken a carbon bike - I'm on my 1st one at the moment, but its a race only bike, so should last a while.

 

Getting to the point - "The fatigue life of a properly designed steel or aluminium bike exceeds your or my lifetime" - yes, if you want it to weigh a lot more. A modern race frame is basically a sacraficial component. There are no meaningful safety factors to cover fatigue etc. The lighter and more expensive it gets, the more this is the case.

 

The solution was simple - find a manufacturer that makes all their frames to the same geomtry, get their race frame and get their tank frame. In my case I have a CR1 limited for racing and an old speedster s4 (heavy 1.6kg ali) to train on.

 

And, I believe, appropriate application of carbon and ali

 

[/quote']I think what you fail to mention is that it doesn't matter what material a frame is made out of - you will break it! You could build a frame out of 50mm mild steel square tubing: you'd complain about the lateral flexing and still snap it behind the BB. Besides the frames - think about all the broken pedals, cranks, bars, saddles etc you have left in your wake...

 

 

[GoLefty!!]

Jammer om te se maar Johan jou fiskika is dan n bietjie af....
You don't have to be able to bend material in order to see if it will provide a softer ride or not...different material absorb vibration better than other' date=' simple example would be how you can hear sound through certain material better than others etc. Carbon absorbs road vibrations better than aluminum, also the reason why steel is such a smooth ride...
Offcourse this all depends on how certain manufactures develop the their frames, so some alu frames might have a softer ride than some carbon frames and visa versa, but if you look at the raw material, carbon WILL give a softer ride...basic physics.
[/quote']

 

You say "steel is such a smooth ride" as if this is fact. I am not so sure this is established. I think most people are brainwashed by stuff they read in bike magazines - aluminium is harsh, steel is smooth, carbon is like triple-ply toilet paper etc etc etc.

 

Since you want to tackle the problem from a vibration and harmonic point of view, lets do that then.

 

Bicycle resonances (vibration, as referred to in these posts) are totally random except for when you drive over something that we can reasonably forsee will give us a specific harmonic - say one of those vibrations strips they now build into yellow lines or a drain grid. Other than that, the frequency is random because the road surface is random.

 

To claim that the frame responds to all of those fequencies is far-fetched. The odd resonation comes from these regularly-spaced purpose-built things on the road. A frame just transmits plain old road shock and doesn't vibrate like a guitar box. The softer your tyres, the less shock reaches you, no matter what type of frame.

 

Further ammo against this vibration argument is the huge damper every bicycle comes with - your body. I once saw a bike gadget salesman demonstrate a damper for handlebars. It was a piece of rubber he inserted - each into one one end of the bar. He dropped the bar and it didn't resonate. He then took the rubber out, dropped the bar and it resonated audibly. I then took the undampened bar, hit is agains the counter and made it resonate. Simply by touching it with a finger, could I stop the resonation. Now imagine how well you dampen it when both hads are clutched around the bar, not to mention the tape, brakes bells and whistles you have on your handlebar.

 

Remember, the resonance of a body is determined by the largest component of the body. A light handlebar cannot resonate when it is dominated by a  pair of heavy arms. Likewise, a silly piece of plastic in a bike's frame cannot stop it from vibrating, the frame is bigger than the plastic. The frame stops vibrating because your body is damping it.

 

The feel of a bike varies from rider to rider and is not something that science can define.

 

An aluminium frame is no harsher than a carbone one. However, undoing years of bicycle magazine damage is difficult to do. Yet, I have never seen a bike magazine define the vibration, determined its frequency and showed the different frequencies of carbon, steel or alu bikes.

 

 

 

 

 

 

 

Ahh, you make an interesting point here Johan. The body of the rider is indeed a large damper but I don;t think that the maker of the damping plugs claims that this is not the case.

 

Damping out vibration has to do with fatigue of the rider. The more the body acts as a damper the faster it fatigues. All that vibration has to be damped by whatever constitutes the body. The higher your body fat the higher the damping.

 

So for tall, big boned or fat people, the damping properties are the frame are largely irrelevant since their body fat will absorb vibrationsbefore the muscle is affected.

 

For leaner, lighter or smaller riders, with less natural damping, the damping properties of the bike frame and other bits plays more of  role in delaying fatigue.

 

 

 

On Frame material:

 

Choice Frame material is one of those fashion things. Buit it is also driven by material prices globally. Yes demnd for Carbon fibre is growing, therefore it is becoming mor expensive. But Carbon Fibre is made from Crude oil and with that hovering around $90-$100 a barrel it's clear that it will become exponentialy more expensive and the therefore more exclusive.

 

I agree that most aluminium frames are "Strong enough" and "light enough" and that it should be the material of choice but aluminium is energy intensive to manufacture.

 

It boils down to the marketing Strategy meeting at Acme Bicycle manufacturers;" Boys how will be get these lycra clads suckers to pay more?"

Answer:" Carbon, carbon carbon

[linnega]

I guess that kinda wraps the original argument.  There is no reason why a well made Alu bike should be better than a well made carbon bike.

 

As an aside, a couple people mentioned tyre pressure as having a significant on road feel with the common statement that softer tyre equals softer ride.  Like the other arguments perhaps this should have been fully explained as there is obviously a point where too little tyre pressure equals a very uncomfortable ride, something I was reminded of the last two days as I rode the last 2km and then 3km on a practically flat rear tyre - not comfortable at all.

[Johan Bornman]

On Frame material:

 

Choice Frame material is one of those fashion things. Buit it is also driven by material prices globally. Yes demnd for Carbon fibre is growing' date=' therefore it is becoming mor expensive. But Carbon Fibre is made from Crude oil and with that hovering around $90-$100 a barrel it's clear that it will become exponentialy more expensive and the therefore more exclusive.

 

I agree that most aluminium frames are "Strong enough" and "light enough" and that it should be the material of choice but aluminium is energy intensive to manufacture.

 

 

Snip snip snip

 

[/quote']

 

 

Fashion it is.

 

But on relative cost: According to a materials handbook I could lay my hands on, the relative manufacturing cost, calculated in tons of oil, of Steel, Alu, Ti  and Carbon looks like this:

 

Per ton of material (I'll leave it to the forum to calculate the relative weight, because a ton of steel does not equal a ton of carbon).

 

Steel:                            1-5 tons of oil

Aluminium                      6 tons of oil

Carbon fibre                  100 tons of oil

Titatnium                        20 tons of oil.

 

 

Per ton of material (I'll leave it to the forum to calculate the relative weight, because a ton of steel does not equal a ton of carbon).

[Gumpole]

out of interest, is carbon made from raw oil somehow (I really dont know!)???

 

surely muscle absorbs vibration pretty well as fat, they are both relatively 'soft' compared to carbon/ steel??

[Joss]

Has anyone ever sat back and had a look at how much you get charged for a carbon part' date=' when there is an aluminium part that weights the same, works the same and costs a fraction of the price? Here are a few examples:

 

Frame: Karbona (and many other) carbon frames at 1.2kg (R6000?) vs Scott speedster alumium frame at 1.2kg (whole speedster S60 bike for R6000)

 

Wheels: Zipp 303 clincher at 1556g (and that was the lowest weight I found) (R12k?) vs Ritchey WCS DS at 1550g (R4000)

 

While carbon made properly (like a scott or cervelo frame) really is lighter than aluminium and/or when properly applied (like a zip 303 tubular wheelset) definately has its place, too many parts these days are carbon for the sake of marketing to attract a higher price without offering material benefit to the buyer.

 

Think about it before spend you hard earned Xmas bonus on a carbon 'wannabe' bits 

 

 

 

[/quote']

 

You obviously do not have any idea what you are talking about. You are comparing a City Golf to a M3 BMW. Rather find out why there are price differences before you start talking k@k about something.