[Closed] How sturdy are rigid carbon forks?

I've had several pairs of Pace carbons and ignore any twaddle/fairy stories about them being compliant - they're still a rigid fork and your arms will hurt if you have lots of rocky trails!!! The main benefit of Pace forks was their lightness.

I can't vouch for their ability to withstand drops as I'm a wheels on the ground type of rider.

I have a set of "exotic carbon" forks, My wheels also stay glued to the ground but for fast cross country work and single track they are ideal. There is a certain twang about them that takes the edge of trail buzz and unless it gets really rocky or rutted I really don't miss my suspension forks.

What about durability?

1ft drop for example?

Hmmm I'd also be interested to hear about this!

I've done 2ft drops on my road bike, get on with it ya big jessy!

i do drops and stuff on mine. never not ridden anything because of forks.

Have to have freeride socks for it though 😉

Back in teh days before suspension folk were doing drops and jumps on rigid steel forks. I'd have thought carbon was stronger, and if they couldn't withstand 1' drops there'd be alot of flaming.

I had some carbon Pace ones. I rode them on a bmx track once or twice, they made some, er, interesting noises but didn't break.

Been running Pace carbon for last 8 years with no problems. They do flex slightly but you get used to it. Durability ? secondhand when I bought them and still seem all ok. Drops ? I've had the odd "whoops to late to brake" and down a 2ft drop moment with no damage done.

My pace ones snapped. I am a xc rider. I don't jump. Forty stitches later and many dentist bills I drew the conclusion they aren't sturdy. Pace said they should be serviced annually... On a fork that has no moving parts? Clowns. I can send you a pic of my face if you want any persuasion not to buy them.

I'd like to see some pics of your broken fork. Never found any horror stories by googling...

The Mg alloy disc mount on mine is split, however. Caused by overtightening the brake bolt, not by riding.

I went back to steel for the MTB for piece of mind and my recently found ability to break everything.

Me and my RC31 at Cwmcarn 🙂

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Yes, that IS tinsel and bows on the bike. Xmas.

On one carbon compared to on one steel, much more comfortable, seem very strong to me, don't ride any differently if I have sus forks, I like em a lot

Carbon fibre is stiff (high Young's Modulus).
Carbon fibre has poor fracture toughness and poor strength under compression but nothing to worry about.

http://www.salient-news.com/2010/04/carbon-fiber-bicycles-dangerous-without-maintenance/

http://www.associatedcontent.com/article/342883/2007_raleigh_cadent_bicycles_with_carbonage.html?cat=27

http://velonews.competitor.com/2010/06/news/steered-wrong-racers-concerned-about-broken-carbon-steerer-tubes_121389
http://www.cervelo.com/en_us/company/support/recalls/

"A damaged
carbon part may appear normal at a quick glance, but could suddenly fail without warning. Carbon forks"
http://www.trekbikes.com/pdf/carbon_care/06TK_Carbon_Care_Flyer.pdf

http://rideyourbike.com/carbonfiber.html
http://www.cpsc.gov/cpscpub/prerel/prhtml07/07211.html
http://www.mtb-news.de/forum/showpost.php?p=2862503&postcount=188

Macavity wasn't it you that said:

Aluminium does lack sufficient fracture toughness, for bike frames.

That reminds me...

personally I would never had a carbon component of an MTB because the catastrophic failure mode scares me.

I am fully prepared to accept this may not be rational but I would never be happy riding the bike

I've had 2 pairs of pace forks and hammered both of them, never really looked after them, and not had any problems, Done countless drops, roll ins, rocky decents and a fair few crashes. Riden all over the lakes, but mainly North Yorks moors and dalby.

Like above they have made some noises. The only reason i don't have any at the mo is that i'm recovering from a broken wrist but when thats sorted i'll be back on them.

I just realised that worrying about carbon forks is pointless. My whole frame is carbon 😆

Has anyone got a pic of a broken carbon fork?

personally I would never had a carbon component of an MTB because the catastrophic failure mode scares me.

I am fully prepared to accept this may not be rational but I would never be happy riding the bike

I know what you're saying but have you never seen a pair of alu handle bars fail? The failure mode is just as catastrophic. You hear a crack then the next thing you know you are picking your teeth out of the stem.

That said, I do find it offputting that it is so easy to kill carbon stuff by overtightening clamps.

Ask Simon about Alu bar failure 😉

Slight Thread take over sorry! but Would clamping a carbon frame on a roof rack be a problem?

Glad I saw this; I'm going to put some exotic forks on my bike for Peak district riding.

www.bustedcarbon.com or whatever has a sample of the millions of carbon components that have broken.

Another pair of broken Pace RC31's over here. Unbonded at dropout and crown = BIN!

Anyone riding steel forks? Kona makes one: http://www.evanscycles.com/products/kona/p2-mtb-fork-disc-only-ec001685
Anyone know the weight of these or comparable ones?

I have some p2's somewhere, they aint exactly light. i thought they where a harsh ride.

Pace rc31s on my Giant xtc. Ridden with them in Rhayder a few times where it can be quite rocky, biggest drop is probably only a foot or so though. They work well round the local woods where I live. Light rider 60kg.

Kev

New Science of Strong Materials: or why your feet dont fall through the floor, a book by J E Gordon.

"Like boron, this fibre has suffered from a great deal of irresponsible Government publicity.
Although frequently described by the newspapers and on television as a wonderfibre of exceptional strength, carbon fibres are not in fact, particularly strong; if anything they are a little weaker than glass fibres. They are however, for their weight, something like eight times as stiff as either glass or the normal engineering metals. As might be expected the resin-fibre composites made from carbon fibres are very stiff but not especially strong in tension. They are also, at present, rather inconveniently weak in compression. While it might be possible, in theory, to put up the compressive strength of carbon fibre composites by using a metal matrix, this does not usually work in practice because of the chemical reactions which occur between the carbon and the metal.

However, for many purposes where weight saving is important but where the strength requirements are not too critical – such as artificial limbs, golf clubshafts or the stiffening of car bodies – carbon fibre composites have been very successful.
When we turn to more exacting applications, like aircraft parts, the trouble is generally lack of toughness. When the composite is made in the conventional way the work of fracture whichis actually achieved is not far short of the calculated theoretical limit – but unfortunately this is, in practice, not sufficiently high."

Yes cynic_al aluminium has limited physical properties (toughness)
Higher strength aluminium alloys do not always have higher FRACTURE TOUGHNESS.

http://emeraldinsight.com/Insight/viewContentItem.do;jsessionid=B098E158DF7197C11F7B9EA2CEB39EA8?contentType=Article&contentId=1682514

"THE highest strength wrought aluminium alloys currently available are based on the aluminium-zinc-magnesium-copper system, and such alloys offer considerable potential for weight savings in airframe structures. However, these alloys have presented problems in service, arising from deficiencies in fracture toughness and fatigue crack propagation resistance together with a susceptibility to exfoliation corrosion and stress-corrosion, which have led to restrictions being placed on their use by individual aircraft companies and by procurement authorities in a number of countries. This situation has led to the wide-spread use in the UK and continental Europe of lower strength alloys of the aluminium-copper-magnesium-silicon type, even though significant weight penalties are incurred in the process. There has been a more general acceptance of the high strength aluminium-zinc-magnesium-copper alloys in the USA, where problems associated with their use have been partially alleviated by a willingness to replace components at short intervals, but even so during recent years a trend has developed there towards the use of lower strength versions of these alloys in attempts to improve airframe durability and reliability. "

Macavity what relevance do your posts have?

I think there are thousands/millions of unbroken carbon and aluminium frames?

Interesting stuff, Macavity.
How does "aluminium-zinc-magnesium-copper" and "aluminium-copper-magnesium-silicon" translate in to the 6000 and 7000 numbers quoted by bike frame manufacturers ?
It's all very well a manufacturer saying they are using a lighter, stronger alloy, but not so good if it's one that's been found unreliable by the aircraft industry.

Oh, and 100kg rider on Nuke Proof rigid carbon forks.
Since snapping two egg beaters clean in half I have given up any aspirations of doing anything remotely radical, dude, and never intentionally get both wheels off the ground at the same time.
I have still managed to snap one aluminium and one steel frame within the past two months, so, I too worry about the fatigue life of my forks every time I hit a set of braking bumps.

Its not fatigue thats the issue - its overloading them. the limits might be high and could well be higher then a metal bit.

But - it you overload carbon fibre it turns to dust. Overload metal it bends. Thats what scares me.

All horribly oversimplified I know

Still waiting for some photos of a broken RC31...

If it's just the crown or dropouts that are damaged Pace can replace them.

Fortunately when my Mary bar broke I landed on grass. Painful but no damage done. And my cranks that snapped didn't me hurt at all - the pedal end just got left behind. Aluminium is evil - I've got a commuting frame that's probably going to snap pretty soon, the corrosion is far worse and accelerates quicker than anything I've seen with steel.

TJ, I'm a mechanic, not an engineer, so I'm not familiar with different failure types.
Generally, if a bus breaks, I weld it back together and add a reinforcing gusset.
I snapped an aluminium frame at the top of the seat tube. Presumably it was the constant flexing and leverage of my weight on the seat that did it.
I snapped a steel frame at the seat and chain stays near the left hand drop out. Presumably it was the torque reaction of the Rohloff hub that did it.
In both these cases the load would have been well within what the frame was designed for,it was repeated small loads that caused a fatigue failure.
When you say fatigue is not an issue for carbon fibre, do you mean that if it survives the first bump, it will survive an infinite number of similar bumps ?
Maybe not quite that literally, but you get what I mean.

Some materials do have high UTS Ultimate Tensile Strength (resistance to being pulled apart), but unfortunately in a three dimensional world there is compression and torsion and a combination of these.
CFRP (Carbon Fibre Reinforced Plastic) was initially developed to have higher specific stiffness (ratio of stiffness to weight) than steel, titanium and aluminium.
CFRP does have fairly good UTS (the carbon fibres can resist the pulling / tensile loads) but not so good compression strength (as the carbon fibres begin to rely on the plastic matrix). Just think rope: how good is it at pulling compaired with pushing?

Fracture toughness is important in dynamically loaded structures such as bikes. Fracture toughness or lack of is one of the more common reasons for bike bits breaking.
Because almost everything has defects in it, all materials. Then the strength of a material will not be the limiting factor, but the ability of a material to resist the effects of these defects. Hence fracture toughness is the measure of how well a material will resist defects, whether surface scratches, inclusions / contaminations, voids, plus a variety of other defects.

Militant Graham
The IADS International Alloy Designation System (for aluminium) http://www.jjjtrain.com/vms/eng_metal_stds/eng_metal_stds_06.html

The digit "6" as in 6xxx designates magnesium and silicon as the major alloys
The digit "7" as in 7xxx designates zinc as the major alloy

There is a relatively readable book Light Alloys by Polmear that gives more info on aluminium.

There are various opinions on what materials are best for bikes:
http://www.kvastainless.com/bicycles.html
even if the bit about rust is odd.
http://www.rivbike.com/article/bicycle_making/frame_materials
very similar style and logic... also odd

cynic-al
what relevance?
Sometimes the lively enquiring mind does wonder why stuff breaks?

"cynic-al - Member http://www.bustedcarbon.com or whatever has a sample of the millions of carbon components that have broken."

Some day I'll found www/bustedaluminium.com, the Metas alone will fill the page to bursting

"MilitantGraham - Member - Oh, and 100kg rider on Nuke Proof rigid carbon forks."

Worth mentioning these are exactly the same as the Exotic ones, just much more expensive. I use the Exotic ones myself and though I haven't exactly hammered them, 40cm or so drop to flat would be the hardest they've had I reckon, they've not done anything odd. I don't do anything on them that I wouldn't do on a set of 100mm XC forks but that's about it.

You can quote any website you want but i am yet to see ANY carbon mtb forks that have snapped through approved use or infact at all. I have seen carbon forks where the legs have seperated from the crown through poor bonding and I have seen this happen on countless sus and aluminium forks.

With carbon being a new and "scary plastic" material there will always be nay sayers generally in most cases those who have never actually used the item in question (very common on this forum).

Companies like Nuke Proof, Pace, Niner, Trek etc that make these products have poured 1000's of £/$ into testing and design so through correct use they are NOT any more likely to break then anyother material.

Bike parts break its a fact, There is NO part/bike that you could put on a site like this that someone somewhere hasn't broken or dislike.

Militant Graham.
This is really rather pushing my (amateur)knowledge but..........
Steel if stressed below a certain point will not fatigue, an infinite number of cycles and it will not weaken. Aluminium will fatigue however it rarely seems to be an issue in MTBs

My understanding is that CF acts like steel - if stressed below a certain limit it will not weaken with fatigue.

When you say fatigue is not an issue for carbon fibre, do you mean that if it survives the first bump, it will survive an infinite number of similar bumps ?

The rolf must have been failing gradually from overloading.

My concern - which I will happily accept may not be rational is about failure mode.

Put an large overload force ( ie in a crash) thru a metal component it will bend and fail gradually. Put the same overload thru a CF product it will fail catastrophically - turning into dust.

Now sometimes the progressive failure of the metal component might occur in a very short time and sometimes there might be a propagating crack that is not noticed leading to what looks like catestrophic failure.

I fully accept that my fears might not be rational - but i could never trust a CF fork.

"Singlespeed_Shep: Companies like Nuke Proof, <snip> that make these products have poured 1000's of £/$ into testing and design"

Nuke Proof buy theirs from a catalogue, the only think they designed on those forks is the logos. Not to say that the actual manufacturer didn't design them well of course, they're the same as the ones I have under a different name and seem great.

Derail mode off 😉 Just annoys me slightly when Nukeproof get away with being largely a rebrander but still charging the prices you'd expect from a producer, like with these, or their pedals etc. There was a post on Bikeradar a while back where someone was insisting Nukeproof pedals were better than Superstar pedals because they were more expensive, exact same pedal though...

i snapped some aluminium handlebars, trust me, it was a very sudden failure and my face hit the ground quite hard.

Thankfully it was in the woods and the ground was soft earth.

Why is when a carbon part breaks, people blame the material??

Carbon fork breaks - its because its carbon fibre
Steel fork breaks - its because its badly made/designed

Interesting links, Macavity, although it does look like someone's been copy & pasting instead of doing their own original research. 😉

I feel a bit more reassured now about the reliability of my carbon forks now. The idea of sudden catastrophic failure is still a bit of a worry though.
Both frames developed a mysterious creak shortly before they broke. I would imagine that if I had searched more thoroughly I would have found the cracks before they spread.
A crack on a steel or aluminium fork may spread slower, but it may still be too quick for me to stop riding before it fails completely.

I'm still curious as to why there is a rule of thumb 80 hour limit for carbon handlebars and no similar limit for frames or forks.

TJ....please please please dont scare people with your theories..

stick to what you do for a day job, and dont come on here as a mechanical/electrical/aero engineer?

please?

scotia - I did say I accepted my fear might be irrational - and then please tell me what is wrong with what I said?

At the end of the day it's down to design and manufacture, rather than material. A correctly designed carbon part will not fail catastrophically as it will be designed not to fail in use. Likewise a steel or alu part. If a steel fork or an alu fork cracks it's because it wasn't designed properly and the material has been taken outside it's safe envelope, just as with a carbon part. The instantaneous failure that seems to scare everyone also scares me. I've not had bars fail, but I've had forks fail. 2 of them. Both steel, but fortunately both instances they bend plastically and were still loosely ridable. Not sure that really matters though as both times I'd crashed and come off the bike in the process. Had they been carbon forks they'd probably have shattered, but I'd still be off the bike.