carbon bikes

smithaay

hi
im a youth racer and looking in too get a new bike i have been offered a nice carbon bike for a good price, however my dad doesnt seem convinced on the strength of carbon fibre compared to aluminium.

i was wondering whether any of you guys would know any tests carried out or articles written about the strength of carbon fibre.

i will just be using it on the road and in races.

i know that carbon fibre is not as strong as aluminium when you hit it with a sledgehammer but that is not realisticaly going to happen whilst cycling. so im just wondering how carbon fibre will handle going over a big pot whole or maybe even a crash.

thanks

lc1981

There's a comparative test (albeit in the workshop, not on the road) here.

smidsy

If it helps CF can often be repaired where an aluminium frame would be scrap with the same damage.

In racing there is always a chance of a crash, so having something that has a greater chance of repair is actually a better strategy than one that relies on a product initially stronger to impact (or have I just used that to justify my bike)?.

curium

smidsy wrote:

If it helps CF can often be repaired where an aluminium frame would be scrap with the same damage.

In racing there is always a chance of a crash, so having something that has a greater chance of repair is actually a better strategy than one that relies on a product initially stronger to impact (or have I just used that to justify my bike)?.

Seriously? I'm not disputing this, it's just that i was always led to believe that damage which would be fine on an Alu bike could lead to sudden, catastrophic failure on a carbon bike.

On a slightly different angle, are there any independent standards for assessing carbon fibre bikes? Different manufacturers call their frames different things (FACT 8r carbon v OCLV carbon) so it's hard to compare quality.

I only ask because it has been put to me that unless you are spending above a certain level you should buy aluminium because the carbon frames will be poor quality.

smidsy

curium wrote:

Seriously? I'm not disputing this, it's just that i was always led to believe that damage which would be fine on an Alu bike could lead to sudden, catastrophic failure on a carbon bike.

I only ask because it has been put to me that unless you are spending above a certain level you should buy aluminium because the carbon frames will be poor quality.

You are not talking about the same thing.

Yes damage on a CF bike will react in a different way to Alu bikes, but that was not my point. I was simply stating that CF as a material is often more repairable than Alu.

Also I was not discussing the merits of cheap carbon. You may be correct on that, but this is also often debated.

ugo.santalucia

smidsy wrote:

If it helps CF can often be repaired where an aluminium frame would be scrap with the same damage.

In racing there is always a chance of a crash, so having something that has a greater chance of repair is actually a better strategy than one that relies on a product initially stronger to impact (or have I just used that to justify my bike)?.

One could argue that the cost of the repair exceeds the cost of a new alloy frame.... :roll:

smidsy

ugo.santalucia wrote:

One could argue that the cost of the repair exceeds the cost of a new alloy frame.... :roll:

Indeed. I had actually thought that after I posted, but a lad has to dream

I thought the idea of this thread was to help convince his dad - not be sensible

Edit: But yes a cheap frame is the obvious correct answer, if a little mundane

curium

Had a quick google and it seems you're correct, although the number of firms offering this service may be limited.

Article in Velonews

Also:

"The repair process is really simple—I do it here for employee bikes," said Brad Paquin, a composite engineer at Specialized. "We could certainly perform that sort of repair [for the public], but once you release the frame back to the customer, you've assumed responsibility and liability. When you factor that in, it's safer for us to just [replace] a frame."

Bicycling

Informative thread. I have learnt something new but I crash way too often to be comfortable with carbon plus the whole hidden damage aspect.

smidsy

curium wrote:

Had a quick google and it seems you're correct, although the number of firms offering this service may be limited.

Article in Velonews

Your level of trust is truly disappointing

RPD Steve of this very forumshire is the man for detailed information.

rolf_f

smithaay wrote:

i know that carbon fibre is not as strong as aluminium when you hit it with a sledgehammer but that is not realisticaly going to happen whilst cycling.

Hopefully, someone will be along shortly to post the video that shows just how wrong you are with the above!

curium

Rolf F wrote:

smithaay wrote:

i know that carbon fibre is not as strong as aluminium when you hit it with a sledgehammer but that is not realisticaly going to happen whilst cycling.

Hopefully, someone will be along shortly to post the video that shows just how wrong you are with the above!

Isn't the problem with carbon fibre (and I'm taking this from F1 team comments) that it is only stronger in certain plains? When it is loaded from a direction it was not designed to be loaded from it is weaker than many metals. This is often demonstrated by an F1 car kissing the wall or hitting a raised kerb and the suspension strut just shattering.
Although I will accept that F1 teams have vast amounts of money to replace CF and are obsessed with weight so the struts may be under-engineered from this aspect.

prhymeate

Rolf F wrote:

smithaay wrote:

i know that carbon fibre is not as strong as aluminium when you hit it with a sledgehammer but that is not realisticaly going to happen whilst cycling.

Hopefully, someone will be along shortly to post the video that shows just how wrong you are with the above!

This one?

http://www.pinkbike.com/news/santa-cruz ... t-lab.html

Wirral_paul

smithaay wrote:

my dad doesnt seem convinced on the strength of carbon fibre compared to aluminium.

smithaay wrote:

i know that carbon fibre is not as strong as aluminium when you hit it with a sledgehammer but that is not realisticaly going to happen whilst cycling. so im just wondering how carbon fibre will handle going over a big pot whole or maybe even a crash.

We better not tell your dad that carbon frames will dissolve in the rain - that'll definitely scupper your plans!

PS your dad is wrong

racingcondor

I've crashed my 5 year old carbon frame twice and it's still going strong.

Unfortunatly the relative strengths of different frames is very hard to quantify. An Alu frame will almost certainly more resistant to side on impacts on the top tube and down tube than a carbon frame (old fat tubed Cannondales excepted, they are tin can thin and flex if you pinch them) but if you're looking for crash resistance I think it's blind luck. In the right plane though carbon is incredibly strong.

I have a friend who crashed an Addict on a descent and had the misfortune of cracking the top tube with his knee. The repair cost £100 and the bike is almost as good as new.

Personally I wouldn't worry about the durability of a >1000g Carbon frame, drop to a <900g frame and you're trading some of that robustness by thinning tubes where they can be and that increases the risk that a small crash will stress a tube in a direction it's not strong enough in.

ricky1980

there is a standard bike safety test which needs to be satisfied by ALL bike frames. it is an ISO EN standard so it is truly international.

But the BB-stiffness/Frame compliance is all manufacturer's marketing tool. very hard to compare like for like for carbon frames let alone carb to alu.

The only comparable results would be have the ISO EN test results. But manufacturer's won't give you those as it will simply put their market money down the drain. That's my cynicism for the fact they won't let out the results.

a 7075 aluminium alloy has Tensile strength of 503MPa and UTS (ultimate) of 572MPa, and the Young's Modulus of 71.7GPa; the difference between 503 and 572 is where the material goes from "elastic" to "plastic" and ultimately fails. so aluminium has a fairy short plastic region when compared with carbon steel for instance Grade 275 which has 275MPa tensile and 430MPa ultimate. so failure is less catastrophic

a T-700 fiber (typical in most mid to high end frames) Tensile Strength of 4900MPa and Youngs Modulus of 225GPa. but carbon is a composite, so the combined carbon + resin's property will vary hugely. usually they are laid in 8 layers and the carbon is unidirectional, with the outer sheet being superficial. that's what i read being the common practice. I think the tensile strength is the ultimate strength. i.e. exceed that the carbon fiber breaks

lc1981

Rolf F wrote:

smithaay wrote:

i know that carbon fibre is not as strong as aluminium when you hit it with a sledgehammer but that is not realisticaly going to happen whilst cycling.

Hopefully, someone will be along shortly to post the video that shows just how wrong you are with the above!

I already got there with the second post in this thread. Still, I do think that a decent aluminium frame remains a better option than a cheap carbon one, if the budget is limited.

ricky1980

carbon fibre itself has excellent strength to weight ratio. better than any material man have had to date. The only other technology is superior is the Carbon Nano-tubes made from Graphene.

ugo.santalucia

ricky1980 wrote:

carbon fibre itself has excellent strength to weight ratio. better than any material man have had to date. The only other technology is superior is the Carbon Nano-tubes made from Graphene.

They are not made from graphene...

VTech

curium wrote:

Rolf F wrote:

smithaay wrote:

i know that carbon fibre is not as strong as aluminium when you hit it with a sledgehammer but that is not realisticaly going to happen whilst cycling.

Hopefully, someone will be along shortly to post the video that shows just how wrong you are with the above!

Isn't the problem with carbon fibre (and I'm taking this from F1 team comments) that it is only stronger in certain plains? When it is loaded from a direction it was not designed to be loaded from it is weaker than many metals. This is often demonstrated by an F1 car kissing the wall or hitting a raised kerb and the suspension strut just shattering.
Although I will accept that F1 teams have vast amounts of money to replace CF and are obsessed with weight so the struts may be under-engineered from this aspect.

This is true, carbon is incredibly strong but also very weak for catastrophic failure when hit or knocked sharply in certain ways. This isnt to say that carbon is not fit for purpose but I did try and suggest the same in a different thread about using them on a trainer where you clamp the lower wheel mount and that being a potential weak point, especially for someone new to cycling being over eager and causing issues which goes inline with many bike companies suggesting lack of warranty with bikes on turbo's.
We find carbon has the best capability to withstand stress but as suggested, when sudden impact arrises it has far less capabilities but then when measured against other materials in the same category nothing comes close.

ricky1980

ugo.santalucia wrote:

ricky1980 wrote:

They are not made from graphene...

are they not? oh, are they extruded from a pool of carbons? they look like graphene rolled up...meh, i wish i did material science in this era. such exciting stuff.

rolf_f

Prhymeate wrote:

Rolf F wrote:

smithaay wrote:

i know that carbon fibre is not as strong as aluminium when you hit it with a sledgehammer but that is not realisticaly going to happen whilst cycling.

Hopefully, someone will be along shortly to post the video that shows just how wrong you are with the above!

This one?

http://www.pinkbike.com/news/santa-cruz ... t-lab.html

Not that one as it happens though it does the job! This is the one I was thinking of....

http://www.youtube.com/watch?v=-lsDXEEUlRE