Thorn Cycles Forum
Community => Thorn General => Topic started by: spoon boy on May 08, 2009, 10:17:06 AM
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I saw recently on ebay a bike that I would call a hard core tourer and it had carbon forks on it..first time I'd seen such a fit
Now many of the hardcore touring bikes stress and stress again that steel is the only choice as one, the steel can be flexed to repair and steel can be repaired almost anywhere in the world so You can imagine then why I was puzzled when this bike from a world renown hard core touring bike company had carbon forks with steel inserts for a front rack
anyway I truly understood the leightweight issue certianly but the strength and application?
I would value any inputs/opinions for future use
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;)
I think these are the forks your refer to
http://www.sjscycles.co.uk/product-Thorn-Thorn-26-Inch--559-1-1-8-Inch-Carbon-Blade-Fork-with-Alloy-Steerer--to-fit-MKI-Thorn-Raven-Tour-and-MKI-Sport-Tour-10735.htm
I memory serves (and it is dodge at best) these were a cost option on the mk1 RT & mk1 RST. I think the forks were aimed more at the Audax rider than the tourer. Where the reputed extra comfort of carbon and the lighter weight they may well of being of use.
I think in the order form it used to say about a restricted load on the forks - but again this is from memory so don't quote me.
On a touring bike, being used as a touring bike, I don't believe there is any place for carbon forks. This is my personal opinion.
Carbon can break without warning especially if loaded in an unexpected direction. Touring bike tend to have a much rougher life than a normal road bike - even mountain bikes tend not to have to put up with baggage handlers!
Stutho
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Certianly Stutho I agree or at least I currently agree
the bike I mentioned could have been any bike and as such carbon forks on a road bike would seem to make a bit of sense but not a lot. You will lose more pounds in cash than in weight saving and to be honest if you want to save a few pounds in weight try laying off the friday vindaloo for a few weeks
I did notice it was an option on some of the thorns and avaliable for other bikes with the thorn being recognised as a hard core tourer I was surpised to see this option
What did puzzle me was they are offered as an upgrade for a hard core touring bike and they have the steel inserts in them to fix racks I genuinely thought this was a contradiction but not claiming to know everything I thought it worth putting out there
Saying that, I know a chap who bought a pace and has never ridden it and also has a whyte prst1 and never ridden that..they hang on his wall so not all hard core tourers will be bought to world or continental tour. Also not all tourers will have front racks or front luggage so in those instances perhaps carbon is a personal non functional thing?
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Its the steel inserts and their tensile strength that interests me, along with the capacity of the bonding process to resist the tensions placed upon it even under a light load
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I'm sure they were engineer stress loaded and tested but the thought in my mind is one of hanging a heavy weight against a plasterboard wall with plasterboard rawplugs..I'd always be waiting for them to fall out
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spoon boy,
>steel inserts in them to fix racks I genuinely thought this was a contradiction
Personally I agree. But looking at it from SJSC point of view (And no I don't work for them) You could say that it would be a contradiction for them to make a fork that fitted a tourer and not include a rack mount! By adding it at least it gave the user the option of using it.
[back to my opinion]
What would worry me most is the kind of load placed on the forks if the rack / pannier was to catch on anything and the torsion (twisting force) this would generate. I am not a expert on carbon but I think that this could be a big no no. (carbon experts please correct me here)
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spoon boy,
>steel inserts in them to fix racks I genuinely thought this was a contradiction
Personally I agree. but looking at it from SJSC point of view (And no I don't work for them) You could say that it would be a contradiction for them to make a fork that fitted a tourer and not include a rack mount! by adding it at least it gave the user the option of using it.
[back to my opinion]
What would worry me most is the kind of load placed on the forks if the rack / pannier was to catch on anything and the torsion (twisting force) this would generate. I am not a expert on carbon but I think that this could be a big no no. (carbon experts please correct me here)
It probably is a contradiction without a rack mount but this has been bypassed with the use of p clips to mount low loaders to forks without eyelets for sometime, and the torsion (twisting force) is exactly what I have in mind as to a barrier to using these for light loads.
Is it possible to get some info from those directly involved in the thorn design dept
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I have a cycle with carbon fiber rear seat stays, which was made by a leading cycle maker, the pr#urchase of this cycle took much thought as it was a xc bike and at the time I didn't know very much about carbon. I took it upon myself to find out about carbon and what it's uses and limitations are. I went into it in quite a depth and with that knowledge I will try to pass on that information.
Carbon is its strongest when a tensile stress is applied to it by the very nature of the material, but it can be manipulated in different ways to react to different stresses ie torsion / sheer and compression. The neat strand that you see on the top layer just under the lacquer is only for aesthetic purposes and serves no purpose at all, the clever weaving of the material underneath is where its strength comes from. By using different methods of weaving and alternating the lamination's different types of characteristics can be achieved.
There is a cyclic yield point with carbon as well which means it reacts similar to steel in it's longevity as a material.
Its poor points are that when its bonded to differing materials for connection to the bike ie if it were a set of carbon forks and the steer tube was steel bonded to the fork crown then this creates issues with regards to differential thermal coefficients, because the two materials expand and contract at differing rates then the point of which they were joined can become parted, If you go for a fork or complete bike then it's much better to have a solid peice of carbon then it becomes as strong as it was intended to be.
Carbon has a nasty habit of breaking with exceeded stress, and can't be repaied easy if at all. Its primary intention was to take alot of the road shock out of racing bikes and i beleive that's were its best kept.
It can look nice but in my opinion there are many downsides to the material than up.
The inserts that are boded in around caliper bosses etc suffer the same expansion problems as the in different material bonding process .
If it were me I would only use steel for it's strength, repairability dependability etc etc
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true the tempreratures of the metal inserts and carbon forks will be different and as such will react differently and I wonder if they will react differently enough to cause issues
My feeling is if you are going to have a dedicated hard core tourer then avoid carbon forks
If however you intened not to use the front forks for weight carrying or front racks then it's a personal choice
I think ?
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I'd not use carbon for forks for touring. This discussion on CTC forum is cautionary: http://forum.ctc.org.uk/viewtopic.php?f=5&t=24386
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Yes there have been cases where the detachment of the two halfs have happened for that exact reason, thats why if you do have carbon forks even on a road bike then you are much better suited to getting a full carbon fork as appose to bonded to a steerer tube but then that has its issues with regards to the fitting of bearings and the forces that they impose on the carbon.
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Excellent post Expr, I can understand fully now the negatives against using them for touring and the use of racks for the reasons pointed out, but the amount of ''stresses ie torsion / sheer and compression.'' that a rack would produce would not be as much as that exerted by the brake caliper bosses would they?
Sorry, Geocycle an informative link, thank you,
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Absolutely right middlesprocket, the callipers will give the most strain around that area by far and the carbon content therefore is beefed up for that reason, and if its designed right by the manufacturer they will endure such strain for considerable time, however as I say the main concern I think as far as touring and / carbon especially anything frame related could end in catastrophic failure through several known facts which is either forced beyond its limit of flex, detachment of bonded parts through expansion contraction or even poor bonding in the first place or if the carbon has taken an earlier knock then this will severely add to any counter damage that occurs in ort round that area.
Then the most important fact of all, you are in a remote area with little means of repair and a broken fork, who you gonna call , well it may as well be ghost busters because your going to need plenty slime around that joint to make it work.
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Ok, bear with me on this.
Where I work I got into a discussion with a few metalwork dept technicians a while back on this subject and they suggested the same weakness as to the bonding as you did. However they also suggested if the steel thread mount was attached to a steel sleeve and the carbon fork was fabricated around this the sleeve then would disperse the load. So you would gain from the weight of the carbon and gain from the strength of the steel inner sleeve
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I would agree with that, by the vey nature of fitting it that way you would be shifting the load away from the area, again by using clever angles and smoothing the area away from the load then this would also help, similar to a brazed frame, if the braze is gently tapered away from the joint then you are encouraging the stress away also but if you finish almost on a butt joint then this is asking for trouble, some manufacturers of frame have tried to adopt the same tecnique instead of using an expanding mandrill to give a double butted / tripple butted frame they have tried variable taper technology to draw away the strain from the joint.
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So knowing nothing about the fabrication of carbon fibre forks, is it possible do you think?
Or should we just discuss Einsteins Unified Field Theory. ;)
Oh I can just see them googling that one, never mind trying to spell it ;D
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This is how the caliper bosses are done already especially on my xc bike, i got talking to the guy who made/ designed the bike and , they are put on a jig and the metal bosses and attachments are wrapped at that stage with the fibre incoporating them into tha stays at that stage, however the mounts that are atthe end of the stays that attach them to the rear dropouts are bonded not sure whybut to me it would have made sense to adopt the same theory as the bosses for the calipers, and again where the seat stay meets the seat post this to is bonded. I guess at that point there is no choice but to do that.
But when all is said and done its only as strong as the bond itself not the steel its bonded to .
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- Unified field theory is sometimes called the Theory of Everything (TOE, for short): the long-sought means of tying together all known phenomena to explain the nature and behavior of all matter and energy in existence. In physics, a field refers to an area under the influence of some force, such as gravity or electricity, for example. A unified field theory would reconcile seemingly incompatible aspects of various field theories to create a single comprehensive set of equations. Such a theory could potentially unlock all the secrets of nature and make a myriad of wonders possible, including such benefits as time travel and an inexhaustible source of clean energy, among many others. According to Michio Katu, a theoretical physicist at City College, City University of New York, those in pursuit of a unified field theory seek "an equation an inch long that would allow us to read the mind of God."
James Clerk Maxwell proposed the first field theory, for electromagnetism, in the middle of the 1800s. Early in the 20th century, Albert Einstein's general theory of relativity - dealing with gravitation - became the second field theory. The term unified field theory was coined by Einstein, who was attempting to prove that electromagnetism and gravity were different manifestations of a single fundamental field. When quantum theory entered the picture, the puzzle became more complex. The theory of relativity explains the nature and behavior of all phenomena on the macroscopic level (things that are visible to the naked eye); quantum theory explains the nature and behavior of all phenomena on the microscopic (atomic and subatomic) level. Perplexingly, however, the two theories are incompatible. Unconvinced that nature would prescribe totally different modes of behavior for phenomena that were simply scaled differently, Einstein sought a theory that would reconcile the two apparently irreconcilable theories that form the basis of modern physics.
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;) ;) See also The Philadelphia Experiment
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I love that stuff on me butties
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So conceivably it could be done that way for attachments for a lightweight rack on a carbon fork for a Sherpa.
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I see no reason why not as its going to be an inherant part of the fork not a juncture.
http://i705.photobucket.com/albums/ww53/daveshell/bike/phonecamera010-Copy.jpg
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I am sure I remember something about carbon seat post's many years ago as well in that there was no visible signs of damage failure before it's actual failure happened at a critical stage and caused injury, broken carbon is very sharp
That said I think it was about the time carbon became fashionable and much money was being made and some less than professional manufacturers/suppliers allowed substandard seat post's onto the market. the bonding of carbon with metal must be done with the highest or professional standards and experience to ensure a safe and workable product
the ability also to use carbon to it's best advantage should be the driving force.
although another world tourer I considered a Koga world traveller, uses alloy and others use steel I still see the term "fit for purpose" in my head and I do not personally have that confidence in carbon forks being used for touring if you are going to use it laden and in a variety of domains and territories
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Yes fit for purpose comes to mind as well with aluminium, what was an exotic grade of material is now a mass produced part of the cycle frame industry. The major problem with aluminium is it starts to weaken from the moment you start riding it. There is no yield point with it which means you have to put more of the material in places where it’s needed and make the frame as stiff as you can.
Aluminium is along the same line of thought as carbon although it’s a little more trusting and unsurprising I think. The cyclic movement of the frame is what will eventually send it to the crusher, it can’t take any kind of bending or flexing and still carry on the way steel does.
Because of the very stiff frame and conveniently placed gussets its gives rather a dull and lifeless ride with little character and feel. It has its place but I don’t think it’s for long term use and again on any sort of repair it’s not so easy to do and it will cause a stress point if you do manage to weld it, which is normally taken out at the manufacture stage by solution hardening.
I have noticed on some of the cheaper carbon posts, they wrap it over an alluminium post first to give the look of carbon but the strength of alluminium.
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http://forum.ctc.org.uk/viewtopic.php?f=5&t=24386
how about the timing on that
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Well well, and then expr said let there be light.