A couple of my mechanic's observations on tubeless and carbon
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This is a great discussion and the point about carbon fiber in aircraft is important. Several of the modern business jets are 75-80% carbon fiber.
However, aircraft structures are (as noted) regularly inspected for cracking and failure, and the QA standards in manufacture are very high. One other distinction is that aircraft structures are loaded differently than bikes. Bikes have much greater concentration of loads than aircraft, particularly at the BB and headtube.
Even more important is mechanical damage. The idea that leaning on the bike at a rest stop could result in a "cracked top tube" is pretty unlikely, however the top tube is the place that a dropped wrench for example could hit and compromise the layup, resulting in a crack propagating from the site of the initial wound.
Mark Petry
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However, aircraft structures are (as noted) regularly inspected for cracking and failure, and the QA standards in manufacture are very high. One other distinction is that aircraft structures are loaded differently than bikes. Bikes have much greater concentration of loads than aircraft, particularly at the BB and headtube.
Even more important is mechanical damage. The idea that leaning on the bike at a rest stop could result in a "cracked top tube" is pretty unlikely, however the top tube is the place that a dropped wrench for example could hit and compromise the layup, resulting in a crack propagating from the site of the initial wound.
Mark Petry
Bainbridge Island, WA USA
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In terms of carbon composites, comparing planes to bikes, is like comparing a cat to a gold fish, in general. much of the composites used in aircraft are big surface areas like wings and controls surfaces. to get a good comparison you would need to compare a specific part that is similar to a bicycle ins sizing or stress, maybe an actuator arm of some sort.
a better comparison might be road to mt.bike carbon frames
a better comparison might be road to mt.bike carbon frames
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Being that many of the carbon bike top tubes are thinned for aero effect, it does not seem unreasonable that you could sit on top tube and crack it. Or from flexing over time by sitting on it. Certain areas are made stronger, others lighter or aero. Also depends on the quality of the bike.
I realize its now popular to sit on the frame going down hill, but those guys have the vast majority of the weight on the pedals and their bikes are free. But maybe that will become a point on future bikes if there are issues that are not necessarily made public.
I realize its now popular to sit on the frame going down hill, but those guys have the vast majority of the weight on the pedals and their bikes are free. But maybe that will become a point on future bikes if there are issues that are not necessarily made public.
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Glue and fabric
All carbon fiber composites - whether on a plane, missile, bike, train or automobile use resin and a carbon fiber matrix. The application is very similar to dope and silk used by the Wright brothers.
The difference in spec is the control of the the tolerance on the different layers you apply to fabricate a omponents. As you track the up from missile boosters to a $ 100K sports car the acceptable tolerance on the resin applied to the carbon in grams per square meter gets smaller and smaller. Likewise the weight of the carbon weave or tynes in a Unidirectional fabric get tighter and tighter.
Aircraft are massively over built for this reason whereas the drive shaft on a high performance super car goes right to the edge - coz the designer knows the spec for the material is so tight they don"t need the same safety margin.
Bikes use a aerospace spec level of carbon prepeg and much is done by hand, a fabrication method the aerospace industry has largely left behind owing to its lack of quality
BMW Audi , Mercedes etc wouldn't risk an ashtray made of military/aerospace spec carbon fiber composite.
You may argue that is an absurd argument. BMW will then ask "How many planes will use your composites this year? You answer '1000 units ! ". They will then say' We will build 4 million units' this year mein klein aschloch! ' and that will be the end of the argument.
The difference in spec is the control of the the tolerance on the different layers you apply to fabricate a omponents. As you track the up from missile boosters to a $ 100K sports car the acceptable tolerance on the resin applied to the carbon in grams per square meter gets smaller and smaller. Likewise the weight of the carbon weave or tynes in a Unidirectional fabric get tighter and tighter.
Aircraft are massively over built for this reason whereas the drive shaft on a high performance super car goes right to the edge - coz the designer knows the spec for the material is so tight they don"t need the same safety margin.
Bikes use a aerospace spec level of carbon prepeg and much is done by hand, a fabrication method the aerospace industry has largely left behind owing to its lack of quality
BMW Audi , Mercedes etc wouldn't risk an ashtray made of military/aerospace spec carbon fiber composite.
You may argue that is an absurd argument. BMW will then ask "How many planes will use your composites this year? You answer '1000 units ! ". They will then say' We will build 4 million units' this year mein klein aschloch! ' and that will be the end of the argument.
Last edited by Johno59; 02-06-19 at 12:35 PM.
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All this discussion about newfangled technologies. Stay safe out there.
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#57
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I find this kind of weird, as I have two (and only two) stop modes: first is when I put a toe down, butt in saddle and the other foot on a pedal, second is both feet flat on the ground, with maybe my crotch gently grazing the top tube. (OK, third is the bike is lying on the ground or leaning up against something and I'm not touching the bike at all.)
A no point is my leg ever resting on my top tube. Am I unique in this respect?
A no point is my leg ever resting on my top tube. Am I unique in this respect?
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I personally had a carbon frame crack on the top tube during my first Belgian Waffle Ride. It cracked in the place where I've seen guys sitting on it, The manufacturer replaced the frame in due time, but I was told by someone at the shop not to rest on the top tube of carbon bikes because that is where the manufacturers can save some weight. This was about four years ago, and led me to start buying steel bikes for my more adventurous rides. I've attached a photo of the crack.
I received a Giant CF frame that was hit by a car, non drive side seat stay snapped clean through the mid-section. The rider was only scrapped up and decided to just reset by force the broken seat stay and continue on!
What I found interesting in examining was how stiff the remaining frame is even with the sheared seat stay.
I also get it that things break and bad things happen. But use your judgement and keep a close eye on your equipment, tools whatever.
I've personally seen including reading enough online (including here) of others mishaps, some very unfortunate. What some risk vs others and how you balance that judgement is always going to be there. Do you park or toss the old carbon bike? Or do you roll the dice?
I think the OP is absolutely wise in sharing this subject. Take or learn what you can from it, calculate in your own mind on what it means or how it affects you. Carry on and safe travels~
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Having read this thread, I have come to disbelieve the mechanic that resting your body on a top tube can cause it to fail. I was undecided when the thread opened. But I do believe he's seeing some kinds of failures frequently. We just don't know the cause yet.
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My immediate thought of current rides in the stable.
1950s Weinmann aluminum cottered crank, still being used in very tall original race gearing in big climbing.
AVA and Pivo stems.
Viscount with aluminum fork.
Teledyne Titan with original titanium fork.
AlAN early carbon tubed, aluminum lugged.
Felt Nine-3 carbon hardtail 29er.
And of course, the subject of using 'numerous' very much aged vintage tubular tires. The horror!!
1950s Weinmann aluminum cottered crank, still being used in very tall original race gearing in big climbing.
AVA and Pivo stems.
Viscount with aluminum fork.
Teledyne Titan with original titanium fork.
AlAN early carbon tubed, aluminum lugged.
Felt Nine-3 carbon hardtail 29er.
And of course, the subject of using 'numerous' very much aged vintage tubular tires. The horror!!
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Peter Sagan says it's okay to sit on the top tube -- at 80 kph. (oh, but I forgot that pro team bikes were disposable...)
Last edited by rm -rf; 02-06-19 at 02:21 PM.
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Other mention in our vintage racing minds is Sean Kelly. Many others too as they had a fleet ready at their disposal. No one has a true count on how many professionally used race bikes were tossed away at season end, but most are. Few kept and or gifted away.
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the top tube is the most vulnerable part of a bike. The Elance thread in this forum shows that, and a carbon bike would probably need a repair from a similar fall. That's why I don't really want a carbon bike. I think they need to make them more robust to hits like that. There is an MTB company that says they have done that, we'll have to see.
The problem with rims is they are too light. Plenty of cracked rims out there that have only been used with tubes. A tube probably does spread the stresses out a little bit more evenly. I am waiting until road tubeless is a little more established. I have heard of problems. I have some 38mm tires I am running tubeless and I would never put tubes in those wheels.
The problem with rims is they are too light. Plenty of cracked rims out there that have only been used with tubes. A tube probably does spread the stresses out a little bit more evenly. I am waiting until road tubeless is a little more established. I have heard of problems. I have some 38mm tires I am running tubeless and I would never put tubes in those wheels.
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My immediate thought of current rides in the stable.
1950s Weinmann aluminum cottered crank, still being used in very tall original race gearing in big climbing.
AVA and Pivo stems.
Viscount with aluminum fork.
Teledyne Titan with original titanium fork.
AlAN early carbon tubed, aluminum lugged.
Felt Nine-3 carbon hardtail 29er.
And of course, the subject of using 'numerous' very much aged vintage tubular tires. The horror!!
1950s Weinmann aluminum cottered crank, still being used in very tall original race gearing in big climbing.
AVA and Pivo stems.
Viscount with aluminum fork.
Teledyne Titan with original titanium fork.
AlAN early carbon tubed, aluminum lugged.
Felt Nine-3 carbon hardtail 29er.
And of course, the subject of using 'numerous' very much aged vintage tubular tires. The horror!!
From the consumer's perspective... well, it's unlikely that you'll experience the failure. It's sort of like playing the lottery, but in reverse.
If you do it a few times, you're very unlikely to experience the failure. If you ride it thousands and thousands of times, then your odds go up quite a bit.
There's certainly value in having fun and interesting bikes, especially if they don't get ridden a lot!
I tend to keep my bikes a long time and put a lot of miles on them... less so for my vintage bikes. I figure I'm taking some chances just using the original stem on my '82 Olmo Competition... hopefully not too much?
I have had a failure on one of my newer bikes.. a broken fork blade on my 2008 commuting bike. I was lucky it didn't break earlier in the day, while coming down a hill at 45mph! There had been other failures of the same type, but I never heard the manufacturer recall the fork. They did send me a new fork, of an improved design, though.
Regarding the original issue... there have been steel frame tubes that were sufficiently light gauge that they reportedly would flex if pinched hard. Not hard to imagine that a CF frame could be similarly designed to handle only the intended loads. Without actual data, though, it's just speculation.
Steve in Peoria
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Without trying to drift from the OP, carbon fiber and bikes go back to the 1970s. Good, bad or indifferent the use of strong cloth and resin continues to evolve and astound.
A few weeks ago I thought more of about when looking over an early Lola champ car chassis with portions of it carbon fiber. Capable of making but yet had not trusted it enough to surround the driver but was used in bulkhead, largely chassis though.
But today, all top race chassis including just about every component is carbon fiber. Wheels, brakes, all suspension links, etc., etc.. Mind boggling the force and stress with these racecraft at speed. And these are far safer racers then those years ago.
Back to bikes. We're discussing frames and wheels but consider all the carbon used in components today, bars, stems, post, shift / trans, bottom bracket, cranks, even flat pedals for the rigors of off-road.
A few weeks ago I thought more of about when looking over an early Lola champ car chassis with portions of it carbon fiber. Capable of making but yet had not trusted it enough to surround the driver but was used in bulkhead, largely chassis though.
But today, all top race chassis including just about every component is carbon fiber. Wheels, brakes, all suspension links, etc., etc.. Mind boggling the force and stress with these racecraft at speed. And these are far safer racers then those years ago.
Back to bikes. We're discussing frames and wheels but consider all the carbon used in components today, bars, stems, post, shift / trans, bottom bracket, cranks, even flat pedals for the rigors of off-road.
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Carbon reflex
CF s greatest attribute is its ability to flex and not weaken. Unlike Al and to a much lesser degree steel, it is unaffected by constant work load cycles. It is half the weight of Al and a quarter of steel's weight. It is 10 times stronger than Al and 3 times steel.
I would have thought sitting on the TT would have zero affect on the TT. CF being monocurque ensures any load is carried by the entire TT and the tops of the seat post and front head tube. A break on the TT suggests to me a pretty serious crash or a rim crunching pothole under full gas..
The possibility of poor lamination of the layers is also poss. One thing unique to CF is delamination between layers carbon and the resin. Prior to a catostrophic failure delaminated bike would feel like ridiimg a marshmallow
Delamination failure is a feature of long term mechanical loads that have occurred on very old and hard worked machines.
The damage above strikes me as self - inflicted and indicates abuse.
I would have thought sitting on the TT would have zero affect on the TT. CF being monocurque ensures any load is carried by the entire TT and the tops of the seat post and front head tube. A break on the TT suggests to me a pretty serious crash or a rim crunching pothole under full gas..
The possibility of poor lamination of the layers is also poss. One thing unique to CF is delamination between layers carbon and the resin. Prior to a catostrophic failure delaminated bike would feel like ridiimg a marshmallow
Delamination failure is a feature of long term mechanical loads that have occurred on very old and hard worked machines.
The damage above strikes me as self - inflicted and indicates abuse.
Last edited by Johno59; 02-08-19 at 05:34 AM.
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BMW Audi , Mercedes etc wouldn't risk an ashtray made of military/aerospace spec carbon fiber composite.
You may argue that is an absurd argument. BMW will then ask "How many planes will use your composites this year? You answer '1000 units ! ". They will then say' We will build 4 million units' this year mein klein aschloch! ' and that will be the end of the argument.
You may argue that is an absurd argument. BMW will then ask "How many planes will use your composites this year? You answer '1000 units ! ". They will then say' We will build 4 million units' this year mein klein aschloch! ' and that will be the end of the argument.
It's mein kleines Arschloch
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Have you ever tried those thorn resistant tubes? In an oversized tire?
They take 10 to 20 lbs or so to fill up the tire.
I had a sidewall blowout in a 20x3 tire. I bought one of those thorn resistant tubes at Walmart and was able to ride (pull the trailer) half-loaded about 20 miles with just the tube holding it together, no boot.
But, for ordinary thinwall tubes (Latex?), I also doubt the tube/tubeless makes much difference when actually riding, although, when mounting, one often over-pressures tubeless tires to seat the bead, and that pop during seating the bead may cause a substantial dynamic force beyond ordinary riding.
Earlier in this thread was the question whether riding tubeless at lower pressures would make one more likely to bump on rocks. Perhaps, but then the dents would be obvious, and a little slight bumping is usually my sign to stop and fix a flat. With the tire taking a fair amount of deceleration, hopefully the rims are designed to a tolerance that they brake with a slight rock bump.
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Well, I don't really know what to think of all of this. But I do have a friend in the bike parts industry. He's working with a company that does c.f. work for NASCAR. As they help him develop his parts they also are testing other companies current products on the market. Most of those products do not even come close to the standards they have to use for the NASCAR parts. Some parts from major companies are surprisingly bad by their standards. Now I guess you can say that the standards needed for the various industry's are different. But for those arguing that C.F. is used for planes and cars and such it might be enlightening to realize how different the standards are.
I have seen some of the test results myself so needless to say there's some C.F. stuff I'll stay away from for sure.
I have seen some of the test results myself so needless to say there's some C.F. stuff I'll stay away from for sure.
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