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A couple of my mechanic's observations on tubeless and carbon

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A couple of my mechanic's observations on tubeless and carbon

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Old 02-08-19, 11:14 AM
  #76  
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The rim cracking issue of carbon rims (which is what I think the OP was referring to) has been a discussion item for years among MTBers, before, during, and after the tubeless evolution. So some guys just refuse to ride carbon rims regardless of tire or tube setup, for good reason - there is no real benefit. I personally don't believe it has anything to do with whether there is a tube involved or not, but would love to see the data. My son cracked a brand new carbon MTB rim from a high end manufacturer on his first ride. I could have ridden that rim for many years and never put the stress on it he does. In fact I'm going to try, because after he warrantys it, he's giving them to me once I find a suitable alloy replacement wheelset for him.
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Old 02-08-19, 11:53 AM
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+1 Watch the documentary on McLaren. Amazing, and they are laying up the stuff in their facility.
Originally Posted by crank_addict View Post
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.

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Old 02-08-19, 12:17 PM
  #78  
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Originally Posted by allig9r View Post
Everything breaks somehow doesn’t it?
in principle,yes... but has anyone ever seen a broken Schwinn Varsity frame?

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(I honestly don't know the answer, but am expecting very few people to say yes)
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Old 02-08-19, 01:33 PM
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Here's a short and way off the 'radar'.

I'll refrain from naming anyone and the who here because I certainly don't want to be liable. But there's no harm in me chit chat in the following.

I personally know and have seen full carbon fiber automotive support jackstands made by a student 'x' at well renowned University 'X' using all tools of the industry made from military only carbon weave and resins donated by longtime aerospace mil contractor 'X'. This was purely student DIY and take me home.... cuz that's what ya learn for the price paid in 'high' education.
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Old 02-08-19, 05:43 PM
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Originally Posted by CliffordK View Post
Not necessarily true.

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.
OK, you got me on that one...
When I was posting I just never credited combining a carbon rim with a tube that must weigh at least double the weight of the rim.
What's more, rubber without matrix reinforcement of some kind exhibits viscoelastic behaviour, in my experience. So even your thorn resistant tube, especially when warm, will tend to keep on relaxing when stretched, over time. In the scenario where it is contained in a tire-rim assembly, I would expect that its contribution to the hoop stress will diminish over time to a residual value.
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Old 02-08-19, 11:29 PM
  #81  
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Originally Posted by old's'cool View Post
OK, you got me on that one...
When I was posting I just never credited combining a carbon rim with a tube that must weigh at least double the weight of the rim.
What's more, rubber without matrix reinforcement of some kind exhibits viscoelastic behaviour, in my experience. So even your thorn resistant tube, especially when warm, will tend to keep on relaxing when stretched, over time. In the scenario where it is contained in a tire-rim assembly, I would expect that it's contribution to the hoop stress will diminish over time to a residual value.
On the same 'weighty' subject, I now wonder how wide the trade off is vs. affecting rotational and mass for climbing. Fat rubber adds heft. And for off-road, you have a basketball effect on non-suspension which is why everyone keeps lowering pressure but rely on air volume. There's a whole lot of other maintenance issues going tubeless off-road too. Burp flats, sealant degradation.

I could see the day where the bikes are all disc brake, carbon rim is married to specific tire and flex bead similar concept to the newly introduced automotive Maxion - Michelin flexible wheel.


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Old 02-09-19, 09:47 PM
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Originally Posted by nomadmax View Post
I'm fully aware that my aversion to carbon fiber isn't rooted in science; for me it's an irrational phobia that it will somehow collapse on me.
I don't trust a CF frame either. I get a bike I love, I want it to last me many years. Unless wrecked or badly abused or stolen, I keep my bikes for years, and choose carefully. I have ridden bikes I like through 2 or 3 drivetrains, through mileage and sheer use. And maintained well. I trust CF in other applications, but on bikes, and bike wheels I tend to remain conservative. I am no weight weenie, I value a balance between weight, and reliability.

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Old 02-11-19, 12:40 PM
  #83  
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Originally Posted by shoota View Post
Again, no. There is a big difference between clamping a carbon and resting on it. And who the heck supports their entire body weight on one leg, on a top tube? Sorry, but nope. I'm willing to bet your guy is seeing damage from handlebars hitting the top tube, not from resting a leg on it.
AH, Bingo--I think. The bar strikes could be like hammer blows on a relatively thin area. So I don't doubt that the mechanic saw these failures but I do think he guessed wrong on the cause.
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Old 02-11-19, 12:43 PM
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Not designed for stress

Having been trained to do non-destructive testing on military aircraft (looking for stress cracks and discontinuities in aircract structures per manufacturers manual) I can easily see how a bike frame can crack if stress is applied to a part of it, that the frame was not designed or stress tested for by the manufacturer. But how does a rider rest their leg on the frame at a stop? I've 9,000 miles of loaded touring, and 2 years as bike messenger, and I've had my leg next to the top tube, but never ON the top tube, at a stop.
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Old 02-11-19, 01:20 PM
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Being most on this C&V thread are mostly into steel frames, you might not like to hear about ultra fragile tubing on today's modern lightest steel. It doesn't take much to crimp.

Cool as they are I have zero interest in an ultra light modern mtb in steel. Will take carbon fiber any day over the super light steel. In addition and should the worst happen, the carbon frames ARE repairable.

Though in all fairness I would expect a CF or ultra light steel race frame as designed only for a race season and then hang it up.

The 99% of cyclist who don't race probably are expecting something more, especially after spending $8000. Then you have others weighing 200 lbs when the frame is designed for a 130 lbs. rider. 💨

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Old 02-11-19, 02:22 PM
  #86  
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Originally Posted by Reynolds View Post
But are there any aircraft where all the major structural parts are carbon fiber, like in bikes?
You mean like the Boeing 787 and, I believe, the A350??? The 787 fuselage is all-carbon. That's a fairly major structural part. Similarly, the control surfaces as mentioned by the previous poster: a) experience considerable stress b) are critical to maintaining stable, controlled flight - failure of one would ruin your day.
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Old 02-11-19, 02:34 PM
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Originally Posted by squirtdad View Post
On carbon, for a while he and a partner sublet space to a guy who did carbon frame repair. The guy did a lot of top tube repairs, right where you rest you leg on the frame at a stop, apparently a lot of high end frames are not designed for this stress
You mean that place where newb home mechanics clamp their expensive carbon frames in a workstand? Nah! Couldn't be that! [/sarcasm]
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Old 02-11-19, 02:57 PM
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Originally Posted by OldChipper View Post
You mean that place where newb home mechanics clamp their expensive carbon frames in a workstand? Nah! Couldn't be that! [/sarcasm]
Positively known of one who did just that. BRAND new and very EXPENSIVE cyclocross carbon fully built. Took it home and that was the first thing he did. Crackola
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Old 02-11-19, 03:11 PM
  #89  
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On one of our Dayton Cycling Club Tuesday/Thursday evening summer rides. I was in the “B” group about 6 or 7 miles into the ride and came upon the “A” group riders all standing around and attending to one of the members who was bleeding and laying in a ditch. My first assumption was that maybe he had gone down when crossing wheels with someone. No! It was something much weirder that none of us would have ever expected. The top tube on his “Stattante” full carbon bike spontaneously snapped during ordinary, moderate tempo paceline riding. IIRC, when it snapped, somehow one of his legs got caught up in the unsupported (broken) top tube and went through the tube leaving a big, circular gash on his inner calf area. I wish I had taken some photos to prove it. They called an ambulance and he was taken to the local ER and got a few stitches.

The inevitable chatter after the fact was surrounding “how can this happen”? There was a lot of talk about how Scattante’ which was Performance Bike’s house brand, made a lower quality carbon fiber product. The guy who it happened to had a perfect excuse to upgrade to a new Cervelo or BMC. AFAIK, prior to the catastrophic top tube failure, his bike had not been subjected to any sort of unusual stress.

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Old 02-11-19, 03:24 PM
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While I have no idea if the mechanic is correct or not about these particular items, I would say this:

I have known a lot of mechanics and they almost always have some kind of weird "old wives' tales" that they believe. Once a guy was insistent that "WD40 corrodes aluminum!" So I always take this kind of stuff with a grain of salt and treat it as conjecture at best unless I see it proven.
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Old 02-11-19, 03:56 PM
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Haven't read all the posts, but the TT photo shows a crack on the top side most likely resulting from a tensile load. The TT is normally loaded in compression, the ST in compression, and the DT in tension. Sitting on a TT would bend it the wrong way and it would crack on the bottom, if at all. But CF strength in tension is very high, and likewise the matrix in compression.
Also, the tube wall stresses are so easily measured with strain gages under full service loading that a material mismatch is pretty hard to imagine, from Specialized or others.
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Old 02-11-19, 03:59 PM
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Originally Posted by clydesdale65 View Post



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.
Now sitting on, I can see. Resting your leg? Nah.
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Old 02-11-19, 04:08 PM
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Anecdotal evidence is what science is based on, right?

The car, tool or cheeseburger are only as good as the upright primates skill that crafted them as it applies to the competence of the clown that purchased them.

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Old 02-11-19, 04:23 PM
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Originally Posted by OldChipper View Post
You mean that place where newb home mechanics clamp their expensive carbon frames in a workstand? Nah! Couldn't be that! [/sarcasm]
I have seen posting in bike forums with manufactures warnings not to transport on bike rack where the bike is supported by the tube.....not even clamped. I also have seen couple of mechanics add padding to the top of their clamps and just hang the bike by the saddle..... and I have no idea at all of how you clamp a carbon, non round, aero mast seat post, never having to do so.
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Old 02-11-19, 05:10 PM
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Originally Posted by squirtdad View Post
Not bashing, but sharing a couple of interesting (or so I thought) observations from my mechanic (don't use a lot, but buy parts from)

This guy as been wrenching for 20 years and works at a shop that builds frames, The sell Rivendell, Jones, etc. the guy works on everything and is not a carbon hater

On Road Tubeless he noted that he saw a tech article from USA cycling noting that there is increased rim cracking without tube usage, due to the pressure of the bead on the rim IIRC, he noted he has seen some rims this way

On carbon, for a while he and a partner sublet space to a guy who did carbon frame repair. The guy did a lot of top tube repairs, right where you rest you leg on the frame at a stop, apparently a lot of high end frames are not designed for this stress
Cheap Chinese tubeless carbon rims are trash - out of four wheels and one new rim every single one of them delaminated at only 80 psi. Four of them the separation was at the bead. One of them went 3" out of true when inflated - this was a delamination down in the aero part of the rim. I am told that there are American made carbon aero rims that do not do this. The prices I've seen is some $2,000 or so for a wheelset.

Aluminum rims such as Campy or Mavic or Fulcrum do not break out here IF you do not have excessive wear. However you have to remain very aware that these new wheelsets are designed to be ultralight and that the braking surface is not long lived.

The cheap Chinese clinchers have a different design around the bead and so these clinchers seem to perform well. But you should always remember that the tubeless delamination shows that the method of manufacture is not all that great and you always have the chance of a clincher coming delaminated at the worst possible time.

Another thing about tubeless tires - you HAVE to have real tubeless tires. They really are different than a clincher with a deep bead area. A real tubeless put together initially and correctly will inflate with a regular floor pump. You do not need these "tubeless inflator pumps". They will also hold air without a sealant in them. Though you shouldn't run them that way.
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Old 02-11-19, 05:17 PM
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I've been sitting on the sidelines on this one. My only comment is who amongst us would buy and ride a 10 year old CF frame, one that had been ridden many miles? 20 y.o.? 30?

I trust steel.
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Old 02-11-19, 05:26 PM
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Originally Posted by crank_addict View Post
Being most on this C&V thread are mostly into steel frames, you might not like to hear about ultra fragile tubing on today's modern lightest steel. It doesn't take much to crimp.

Cool as they are I have zero interest in an ultra light modern mtb in steel. Will take carbon fiber any day over the super light steel. In addition and should the worst happen, the carbon frames ARE repairable.

Though in all fairness I would expect a CF or ultra light steel race frame as designed only for a race season and then hang it up.

The 99% of cyclist who don't race probably are expecting something more, especially after spending $8000. Then you have others weighing 200 lbs when the frame is designed for a 130 lbs. rider. 💨
Carbon is not very repairable. I would not trust it. Older carbon frames are not very trustworthy either. The problem appears to be that they tried to build them like metal bikes. So there were really high loadings around the junctions such as the head tubes. You CAN build a perfectly safe carbon frame but then it isn't particularly light. More lately they've changed the resin so that it is completely hardened from the factory and they design the junctions to spread the loads as widely as possible so that at any point the loads are relatively light. It remains to be seen since people like Colnago will only issue a two year warranty on a frame though Specialized and Trek give lifetime WARRANTIES. Remember - that is not a guarantee. Modern ultralight steel frame may not be any more reliable.

This is not to put people off with scare stories but to let you know that modern bikes built for performance are not built for reliability. Buying the lightest carries with it the inevitable chance that it could break. So chose your weapon with care.
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Old 02-11-19, 06:08 PM
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Originally Posted by RiceAWay View Post
Carbon is not very repairable. I would not trust it. Older carbon frames are not very trustworthy either. The problem appears to be that they tried to build them like metal bikes. So there were really high loadings around the junctions such as the head tubes. You CAN build a perfectly safe carbon frame but then it isn't particularly light. More lately they've changed the resin so that it is completely hardened from the factory and they design the junctions to spread the loads as widely as possible so that at any point the loads are relatively light. It remains to be seen since people like Colnago will only issue a two year warranty on a frame though Specialized and Trek give lifetime WARRANTIES. Remember - that is not a guarantee. Modern ultralight steel frame may not be any more reliable.

This is not to put people off with scare stories but to let you know that modern bikes built for performance are not built for reliability. Buying the lightest carries with it the inevitable chance that it could break. So chose your weapon with care.
As mentioned, how light does one have to ride vs risk? The makers get it. But many buyers don't.

You want it because the guy next to you has one and that guy said its lighter than even the UCI says no go to the pros!

All need to use their best judgement and research.

That said, there's many ways to build carbon frames and they are repairable. Its rapidly evolving. New rapid production in raw material to application. Cost is coming down. So much that the automotive industry is ramping up for use even in the lower budget models. Carbon entry level race bikes are pretty impressive and cost a fraction of steel customs.

I love vintage steel (including some vintage aluminum and carbon frames), not just to park and talk, but do experience them. I've also seen many R-531 steel framed bikes presented with dings and dents if they fall over too. I've seen the finish marred on a carbon bike after falling over but not cracked.

I road back when early carbon monocoque off-road hardtail. Crashed and banged. Paint chip only. They're completely different vs today, but for comparison to very lightweight MTB in steel back then, the Kestrel was most robust. These days I ride a hardtail carbon 29er. I'm most impressed. I realize its a different animal vs carbon road bike layup but I'm not against owning one.
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Old 02-12-19, 01:06 AM
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Originally Posted by gugie View Post
I've been sitting on the sidelines on this one. My only comment is who amongst us would buy and ride a 10 year old CF frame, one that had been ridden many miles? 20 y.o.? 30?

I trust steel.
I trust steel implicitly. Vintage welded aluminum (a la Cannondale) as well.

As to your question, I would buy and ride one. It would be an in-person purchase only, and a lot of going over it and looking at clearcoat condition for any potential issues current or to be. Now, there are not a lot of super tall 10+ year old CF bikes around...that look decent. A lot of stuff less than 10 years, and given the same inspection, I'd ride those. For a 30 year old one, say those CF/aluminum Team Miyatas that were sold (someone on here has one) but are otherwise complete unicorns, I'd ride a clean one.

I suppose it says a lot about my level of trust (foolishness?) when I buy and build up a 1980 Trek 412 with bright orange rust powder in the bottom of the inside of the top tube (no internal rust anywhere else) and paint bubbling. Zero problems with it, and would build it up again and ride it long distance. [Currently it's just resting as a frame, fork and headset. Not selling it though!]
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Old 02-12-19, 03:02 AM
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Is this what we are talking about? A picture is worth a thousand words.


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