Road Cycling - 12k Carbon vs. 3k Carbon

Calling all Material Science Engineers!!!!


I was looking at different carbon frames and noticed that some were made of 3k weave and 12k weave. I thought that 12k carbon was "better" but stumbled on a document:

http://corecomposites.com/media/penetrationImpactTestResults.pdf

On page 4, the graph depicts load vs. displacement and tells me that 3k is stiffer (less ductile) than 12k by a lot it seems. It appears that 12k is way less stiff than 3k by the graph (I may be reading it wrong though...).

Otherwise 12k has more desired properties (higher tensile strength...ect...)

What are your thoughts?

What weave does your bike use????

Thanks,

purely cosmetic

Thanks!

That tensile test you're looking at is not a traditional tension test. It's a "shear deformation test" as the title states. Also, it shows 12k having the same modulus (elongation vs. stress) as 3k but much higher elongation before failure and ultimate strength. Page 9 confirms this.

Higher ultimate strength and elongation means tubes can be thinner and lighter.

Also, read page 12, it's pretty self explanatory.

12k>3k

purely cosmetic
Not the cosmetic top-layer, he's talking about the construction.

Overall, from my understanding, 3K is the workhorse of carbon fiber. It's light, relatively stiff and easy to get and make. 12K is a heavier material, but is also stronger and stiffer, so a layer or two would probably be used in critical high-stress areas like the BB aree, HT area and the chainstays.
Hopefully I'll be getting experience on carbon layup in college.

Thank you, I was reading that wrong... (BioE major ;))

I'm in the industry... 12K means there are 12,000 filaments per "tow" and 3K means there are 3000. The stiffness and strength are indicated by other numbers. There are many grades of fiber though and most can be had in 3K, 6K, 12K some in 24K and even up to 50K. I think I've seen some bikes that say "high Modulus" in a decal. I've never checked, but they must be using some "hi-modulus" fibers in building them. An example would be Toho's G55-700 vs. their G30-500 carbon fiber. 55msi modulus vs. about 34msi and tensiles strength of 700ksi vs. 550 to 600ksi. The higher these numbers go, typically the higher the price of the fiber. I'm pretty sure I can buy both of these fibers in 6K and 12K.

Modulus can go up to about 135msi, but not in bicycles because the fiber is $1500 per lb. and the tensile strength is lower, causing it to be more brittle. There are actually many grades of carbon fiber but only a few are used in bikes.

Because 3K is a smaller bundle of fibers, thinner fabric can be woven than with 12k, or thinner tubing can be filament wound, but if the fiber is the same grade, stiffness and strength are not affected by tow size.

Jim

^^^ Wow, now I know who to talk too...

Thanks a lot jleslie, you answered many unanswered questions.

~9k.

Bike enthusiast, I just glanced at the article you were reading. The 12K is T700 and the 3K is T300. Toray's T300 fiber is the "old standard" in the industry. Their T700 is newer and has much higher tensile strength than the T300, regardless of tow size.

Jim

Bike enthusiast, I just glanced at the article you were reading. The 12K is T700 and the 3K is T300. Toray's T300 fiber is the "old standard" in the industry. Their T700 is newer and has much higher tensile strength than the T300, regardless of tow size.

Jim

Thanks again... So are you saying that most of "today's" bikes are T700?

56.6k (modem style)

I'm looking at buying some 3 spokes carbon wheels. they come in the 3K or 12K. Reading the discussion going on and being a novice with such things, can anyone confirm which I should
buy?

Here is an interesting if not biased discussion from a German frame mfgr.
http://www.storckbicycle.com/usa/index.php?c=tech&s=carbonfiber

There is also a discussion in the frame building forum.

Bottom line... I'm still confused. All I know is I love my CF bike. nuf said.

I'm in the industry... 12K means there are 12,000 filaments per "tow" and 3K means there are 3000. The stiffness and strength...<snip>

Good post. :thumb: