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OMG! Plastic is lighter than Carbon!

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OMG! Plastic is lighter than Carbon!

Old 04-07-07, 06:51 PM
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OMG! Plastic is lighter than Carbon!

I got a chance to weigh four 5mm plastic headset spacers and 5 similarly sized carbon spacers. The plastic ones are lighter by 3 grams.

All this talk about advance in material science is starting to not make any sense. For parts that are not designed to bear stress, such as the shifter levers, rear + front derailleur plates, and seatpost, I would love to see lighter plastic replacing CF. One request: for the newly designed Sram Galaxy (above sram force and rival), I would love to see plastic levers instead of CF.

Overarching assumption: CF is NOT plastic
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Old 04-07-07, 06:52 PM
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Originally Posted by samsation7
I got a chance to weigh four 5mm plastic headset spacers and 5 similarly sized carbon spacers. The plastic ones are lighter by 3 grams.
Did it ever occur to you that weighing 4 plastic spacers and 5 carbon ones might give you slightly skewed results?
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Old 04-07-07, 06:56 PM
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Originally Posted by bdcheung
Did it ever occur to you that weighing 4 plastic spacers and 5 carbon ones might give you slightly skewed results?
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Old 04-07-07, 06:58 PM
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Originally Posted by bdcheung
Did it ever occur to you that weighing 4 plastic spacers and 5 carbon ones might give you slightly skewed results?
that's a typo. 4 CF spacers not 5.
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Old 04-07-07, 06:58 PM
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Seatposts weren't designed to bear stress?
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Old 04-07-07, 07:00 PM
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Must be all that stress from the Harley incident....
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Old 04-07-07, 07:01 PM
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Originally Posted by ViperZ
Must be all that stress from the Harley incident....
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Old 04-07-07, 07:10 PM
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I think they use carbon for it's strength, weight for weight.
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Old 04-07-07, 07:56 PM
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Plastic versus carbon in a tensile test would be a joke. Plastic might be a little bit lighter, but carbon fiber has a serious strength to weight ratio while plastic does not.

Plastic is also not as pretty or expensive.
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Old 04-07-07, 08:28 PM
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The other problem you have is that in order to make plastics resistant to creeping under a load, they are typically glass or mineral filled. That added glass or talc in turns ups its specific gravity above that of CF and kills this whole argument.
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Old 04-07-07, 08:30 PM
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This thread is ridiculous. How can you think that companies invest thousands in R&D just to come up with a product that is supposedly heavier than an ancient material like plastic?
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Old 04-07-07, 08:38 PM
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Originally Posted by Jose Perez
The other problem you have is that in order to make plastics resistant to creeping under a load, they are typically glass or mineral filled. That added glass or talc in turns ups its specific gravity above that of CF and kills this whole argument.
Not to mention this turns them into a composite like carbon fiber anyway.
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Old 04-07-07, 08:56 PM
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You need to understand the difference between density and strength to weight ratio.

Are you are saying that standard unreinforced plastic is a better choice because it is lighter for structural applications? If that logic is true, we should be making frames of styrofoam.

Materials in order of tensil strength (not even strength to weight ratio comparison):
Carbon Fiber (5650MPa Ultimate Strength)
Glass Fiber
Aramid Fiber (kevlar)
Steel (1650 Yield Strength, 7.8g/cm)
Titanium
Aluminum
Thermoset Plastics
Thermoplastics (nylon, lexan, etc)


Material Yield strength(MPa) Ultimate strength (MPa)Density(g/cm3)

Steel, high tensile 1650 1860 7.8
High density polyethylene (HDPE) 26-33 37 0.95
Titanium Alloy (6% Al, 4% V) 830 900 4.51
Aluminum Alloy 2014-T6 400 455 2.7
Glass (St Gobain "R") 4400 (3600 in composite) 2.53
Carbon Fiber N/A 5650 1.75
Aramid (Kevlar or Twaron) 3620 1.44
Nylon, type 6/6 45 75
Carbon nanotube N/A 62000 1.34

Last edited by texascyclist; 04-07-07 at 09:23 PM.
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Old 04-07-07, 09:01 PM
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[QUOTE=
Plastic is also not as pretty or expensive.[/QUOTE]

not pretty? Important for some people. Not Expensive? Wouldn't that be good for consumers ?
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Old 04-07-07, 09:05 PM
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Originally Posted by cedricbosch
This thread is ridiculous. How can you think that companies invest thousands in R&D just to come up with a product that is supposedly heavier than an ancient material like plastic?

Do you accept everything they tell you? For example, the carbon plate in record and chorus rear derailleurs and the carbon plate of the front der. serve what functions besides aesthetic?
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Old 04-07-07, 09:09 PM
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For those that are interested good old fashioned measurements instead of "I think this or that", wikipedia has a good list of tensile stregths and density's:

http://en.wikipedia.org/wiki/Tensile_strength
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Old 04-07-07, 09:14 PM
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Originally Posted by samsation7
Do you accept everything they tell you? For example, the carbon plate in record and chorus rear derailleurs and the carbon plate of the front der. serve what functions besides aesthetic?
Agreed, those are purely aesthetic. However, when the material is being used in vast quantities (i.e. frames) there MUST be a significant advantage to justify spending.

Pro teams are a good example- they are obviously unconcerned with aesthetic, yet do you see anything BUT carbon frames in pro tours?
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Old 04-07-07, 09:16 PM
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Originally Posted by samsation7
Not Expensive? Wouldn't that be good for consumers ?
Not for some people. Some people like other people to know they're wealthy. I believe the term is "conspicuous consumption," and it has a strong market in pretty much every area of American life.

That, combined with OCP, ensures that carbon is here to stay.
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Old 04-07-07, 09:24 PM
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Originally Posted by nobrainer440
Not for some people. Some people like other people to know they're wealthy. I believe the term is "conspicuous consumption," and it has a strong market in pretty much every area of American life.

That, combined with OCP, ensures that carbon is here to stay.
I had to read Thorstein Veblen's Theory of the Leisure Class so I have an idea of the term. I just wish manufacturers would make products for another market niche: beginner-intermediate racers with not too much money to throw away and currently have huge school loans. For this niche, I would love to see cheaper (but relatively ligh) stuff replacing CF.
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Old 04-07-07, 09:25 PM
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Originally Posted by nobrainer440
Not for some people. Some people like other people to know they're wealthy. I believe the term is "conspicuous consumption," and it has a strong market in pretty much every area of American life.

That, combined with OCP, ensures that carbon is here to stay.
Are you the same nobrainer440 that posted previously or am I going crazy
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Old 04-07-07, 09:26 PM
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Originally Posted by samsation7
I had to read Thorstein Veblen's Theory of the Leisure Class so I have an idea of the term. I just wish manufacturers would make products for another market niche: beginner-intermediate racers with not too much money to throw away and currently have huge school loans. For this niche, I would love to see cheaper (but relatively ligh) stuff replacing CF.
You already have it.

It's called steel.

Design engineers always say:

You can have it cheap and light but you can't have it strong
You can have it cheap and strong but you can't have ith light
You can have it light and strong but you can't have it cheap

Because of the demand for carbon fiber in the free market society, and the manufacturing processes required to make it, you will probably not see it come down in price for a long time. There is not some kind of cycle manufacturer conspiracy to make the lightest material expensive.

I design interior components for 40 million dollar business jets. The carbon fiber honecomb panels I spec out are never seen again when the wood veneer goes on them. Do you think we just like to throw money away?

Last edited by texascyclist; 04-07-07 at 09:37 PM.
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Old 04-07-07, 09:27 PM
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Originally Posted by cedricbosch
Agreed, those are purely aesthetic. However, when the material is being used in vast quantities (i.e. frames) there MUST be a significant advantage to justify spending.

Pro teams are a good example- they are obviously unconcerned with aesthetic, yet do you see anything BUT carbon frames in pro tours?
Would the carbon derailers have any weight benefit? However negligible that may be. Just asking, as that's what I assumed.
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Old 04-07-07, 09:31 PM
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Originally Posted by texascyclist
Are you the same nobrainer440 that posted previously or am I going crazy
Yeah, but come one, he makes a lot of sense. As CF wheels becoming a little cheaper, I've spotted many overweight, out-of-shaped folks on CF tubulars going at 12 mph on flats.
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Old 04-07-07, 09:32 PM
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Originally Posted by gabdy
Would the carbon derailers have any weight benefit? However negligible that may be. Just asking, as that's what I assumed.
probably 2 grams...but you can find the definite answer over at weight weenies.
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Old 04-07-07, 09:37 PM
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Originally Posted by gabdy
Would the carbon derailers have any weight benefit? However negligible that may be. Just asking, as that's what I assumed.
Yeah, there is a weight difference between, say, record and dura-ace, but whether that difference is due to the CF derailleur cover or the overall design, is hard to say.
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