Author Topic: Carbon forks vs aluminum or steel forks revisited  (Read 13064 times)

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Offline lily

Carbon forks vs aluminum or steel forks revisited
« on: July 14, 2010, 09:06:37 pm »
A friend of mine just very recently witness an almost fatal bike accident, where the front carbon forks on a cyclist bike collapsed without warning! It made be think about my Bianchi cyclocross with carbon forks. It also makes me wonder about the long term durability of carbon components and carbon bikes. Any way, please look at the link below and give me your expert opinion.. http://www.salient-news.com/2010/04/carbon-fiber-bicycles-dangerous-without-maintenance/
As it stands, I already have 5000 miles on my Bianchi cyclocross, and I will be changing the forks, but I am thinking for aluminum. I know this may sound like a silly question, but are there titanium forks, and if so, do any of you have experience with such forks? Thank you Lily

Offline aggie

Re: Carbon forks vs aluminum or steel forks revisited
« Reply #1 on: July 14, 2010, 11:42:58 pm »
According to the article there apparently was a manufacturing defect.  No matter what the material if there is a defect it will fail.  That includes metal. 

Offline CastAStone

Re: Carbon forks vs aluminum or steel forks revisited
« Reply #2 on: July 15, 2010, 12:10:24 am »
No one has ever done any systematic, large-N, independent testing to verify manufacturers claims that carbon fiber is stronger than metal, but in theory it should be. The problem with both materials is that manufacturers try to put as little material as possible into the bikes to make them lighter, at the expense of strength. However, this is probably not an issue on any Cyclocross bike like you have; they're made to be strong.

P.S. don't take me as an expert opinion, just someone whose been looking stuff up on the internet.
« Last Edit: July 15, 2010, 12:12:32 am by CastAStone »

Offline lily

Re: Carbon forks vs aluminum or steel forks revisited
« Reply #3 on: July 15, 2010, 12:41:46 am »
According to the article there apparently was a manufacturing defect.  No matter what the material if there is a defect it will fail.  That includes metal. 

Aggie, that is true, but metal or aluminum will show warning signs. Well, I will have to see what I decide about forks, but I do love the lightness of carbon for sure.

Offline whittierider

Re: Carbon forks vs aluminum or steel forks revisited
« Reply #4 on: July 15, 2010, 12:55:59 am »

From the article:
Quote
If you are a bike rider it is important to maintain your light bike by performing a fork replacement every 4000-5000 miles

Oh my goodness what a bunch of baloney!!!  When this came up on the tandem forum, Craig Calfee himself posted that he had recently heard from a couple of different customers of his carbon bikes who each independenly said he had over 130,000 miles on the bike and it handled just like it did brand new.

Carbon does not fatigue like the metals do.  If it makes any difference, the only fork I've seen break on the road was aluminum.  There can of course be a manufacturing defect, but even most carbon failures, whether from a manufacturing defect or an accident, give plenty of warning so you can stop riding it before it causes an accident.  BTW, if you get in an accident, it's more important to replace aluminum bars than it is carbon.  I know people who have broken aluminum bars suddenly and it's usually pretty nasty.  I know one man who broke (actually just fractured) a carbon bar, but it was not catastrophic.  It held on, but he couldn't put pressure out at the end anymore as it was extremely flexible at the break area.

Our younger son was going 25mph a couple of summers ago when someone turned illegally in front of him, and, having only one hand on the bars and a water bottle in the other hand, he sailed right into the car.  He went flying, broke his collar bone and his nose, but I sent the frame and fork to Calfee for their thorough inspection and tests, and they found no damage to the carbon itself so he's still riding the same bike with a lot of new components.  The force of the impact was so great that it even deformed the front hub shell and bent the axle a little.

We have a friend who was in a nasty accident a couple of years ago on his carbon Trek, and hit the right seat stay on the curb hard enough to have a thick 5" bundle of fibers sticking out.  He keeps riding it, and mostly in the local canyons.  He says he has some stuff from his son to fix it but hasn't gotten around to it.  I hope I can get a picture before he fixes it, because it is truly impressive.  His son works at a place that makes carbon fiber rotor blades for military helicopters, and says they have to be able to take 100 hits from a .50-caliber machine gun without failure.

Age and fatigue themselves are non-issues with carbon.  Lennard Zinn asked CF fork manufacturers about the life expectancy of the product.  Here's what they said.

Preston Sandusky at Kestrel says, <quote> For carbon forks in general, there should not be any limited life span, as carbon composites themselves are not subject to fatigue failures as metals are.  So the fatigue life of a properly made carbon composite is "infinite".
<end quote>

Ming Tan at Look says, <quote> There is no limitation because carbon has a natural flexibility.  It can be used a hundred years while maintaining the same stiffness.
<end quote>

Fulvio Acquati at Deda says, <quote> Carbon lasts longer than metal.  Only love is stronger than carbon.
<end quote>

John Harrington at Easton says, <quote> The good news is the fatigue life of carbon fiber is immensely more than that of metals... there is nothing to worry about in terms of fatigue life on a composite fork...In general terms, a component made from carbon fiber will far out-last a component made from metal.
<end quote>

Quote
No one has ever done any systematic, large-N, independent testing to verify manufacturers claims that carbon fiber is stronger than metal, but in theory it should be.

Bert Hull at True Temper says, <quote> ASTM standards call for a load of 170 lbs. applied perpendicular to the steering axis, both pushing and pulling for 50,000 cycles without failure.  At True Temper, every Alpha Q model is tested to 250,000 without failure before a design is considered acceptable.

True Temper's own test is also used on every new model and in routine quality checks.  Our test is a ramped load, meaning the load is increased periodically until failure occurs.  Starting at 180lbs, the load is increased 45 lbs. every 5000 cycles...Our minimum standard begins at over 15,000 [cycles] at 315 lbs. for road forks and 18,000 for cross forks and tandem.  But our production forks are stronger than that, often going into the 20-25K range and beyond at loads 0f 360-405 lbs.
<end quote>

Convinced?

Offline CastAStone

Re: Carbon forks vs aluminum or steel forks revisited
« Reply #5 on: July 15, 2010, 07:46:14 am »
whittlerider - I understand your point, and I believe you, I'm just saying there isn't anything independent about a company that produces the product. I would love to see a research university or a magazine like Consumer Reports spend $100K and really put carbon and aluminum through the ringer.

lily - Aluminum and Steel will NOT necessarily show any signs of fatigue before snapping. I broke a metal crank arm one time while cranking up a hill; it just clean snapped in half with no warning and I nearly broke my leg. Like I said, if your worried about durability, stick with the cross bikes.

Offline rvklassen

Re: Carbon forks vs aluminum or steel forks revisited
« Reply #6 on: July 15, 2010, 08:57:29 am »
As it stands, I already have 5000 miles on my Bianchi cyclocross, and I will be changing the forks, but I am thinking for aluminum. I know this may sound like a silly question, but are there titanium forks, and if so, do any of you have experience with such forks? Thank you Lily
Compared to steel or titanium, aluminum is both brittle and unforgiving. 
Brittle: Aluminum can bend very little before it will starts to lose its strength - whereas steel and titanium are both more able to spring back. And steel can actually be bent without a serious loss of strength.
Unforgiving: The reason many aluminum bikes have carbon forks isn't just to save a little more weight.  It makes the ride less harsh. 

There are titanium forks, as far as I know they are only used on all-titanium bikes.  And sweet as it would be, my pocketbook and an all-titanium bike are incompatible.

Offline aggie

Re: Carbon forks vs aluminum or steel forks revisited
« Reply #7 on: July 15, 2010, 11:15:10 am »
Whittierider is right on.  They also make military jets out of carbon fiber (FA-18 is one).  They pull a lot more stress over time than you'll ever see on a bicycle.  

At jury trials experts are bought.  If you are willing to pay I'm sure you can find a Ph.D. to say anything you want.
« Last Edit: July 15, 2010, 11:19:29 am by aggie »

Offline waynemyer

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Re: Carbon forks vs aluminum or steel forks revisited
« Reply #8 on: July 15, 2010, 12:03:30 pm »
Independent testing: http://www.sheldonbrown.com/rinard/EFBe/frame_fatigue_test.htm.  The results are impressive.
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Offline whittierider

Re: Carbon forks vs aluminum or steel forks revisited
« Reply #9 on: July 15, 2010, 01:53:59 pm »

Quote
lily - Aluminum and Steel will NOT necessarily show any signs of fatigue before snapping. I broke a metal crank arm one time while cranking up a hill; it just clean snapped in half with no warning and I nearly broke my leg.

On another topic I pulled up a lot of pictures of broken aluminum crank arms and steel BB spindles.  There seemed to be an endless supply, although fortunately I myself have never had one of these break.  I did have an aluminum aerobar break a couple of years ago, but that's nowhere near as bad as having an aluminum drop bar suddenly break off in a sprint, or a metal fork steering tube break.  Without an actual break, I've had a Look pedal let go in a sprint and my leg fly up because the release tension wouldn't go high enough, and that's scary enough!  (I use a different brand now that has much higher release tension than any of the Looks.)

Quote
Independent testing:  [I had to omit the URL to make waynemyer's quote show.  Forum software bug?]  The results are impressive.

And note that the steel frames tended to break first.  None of the actual carbon broke.  The only carbon frame that broke broke at an internal aluminum lug, which I don't think any manufacturers use anymore.

Offline ducnut

Re: Carbon forks vs aluminum or steel forks revisited
« Reply #10 on: July 29, 2010, 05:27:55 pm »
 
Brittle: Aluminum can bend very little before it will starts to lose its strength - whereas steel and titanium are both more able to spring back. And steel can actually be bent without a serious loss of strength.

This has far more to do with the qualities of the material chosen, than a blanket statement of "steel or aluminum does this". There many different types of aluminums and steels and they all have different characteristics.