eja_ bottecchia

TiHabanero

clydesdale65
, the shop I worked in for over 30 years and is a Specialized dealer had a Tarmac and a Roubaix come through with this same defect. Model year 2010. It is a real issue, however SBC was unable to determine the true cause of the cracking. Doesn't make sense that a leg in resting position can do this, however when I was racing we often sat on the top tube of the bike while chatting. This may be enough to do it, but I don't really know.

eja_ bottecchia

crank_addict

I had a carbon monocoque Kestrel mtb just after their very first model. This was around 1991 and the CS-X model. Full rigid stock fork -a steel Ritchey Logic and I also had the first full carbon flat bar made by Aerosports. That bike was regularly ridden off road and hard. When Specialized came out with their first shock, called Future Shock, essentially a Rock Shock air/oil, this was installed and the bike was ridden even harder. Never, ever had an issue!

Today I have a very current carbon hardtail 29er. I ride it solely off road for what its designed for. (Key words designed for). I'm not afraid of riding it hard. The modern mtb's have greatly evolved and remarkable machines.
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Back to the 'road' carbon clincher tubeless.

Unlike aluminum rims that dissipate heat, the carbon clincher doesn't, which therefore causes problem of softened weakening resins. Think of the high pressure road clincher and force upon that carbon hook.

Again, this is not an issue with tubular type.

But, that's soon to be changing as disc brakes evolve on road bikes, taking any issues of heat away from a rim. Though as one might guess, another problem for road disc is heat.....

RobbieTunes

He was just relating what a mechanic told him about a guy who repairs carbon frames.
Not sure he outlined the mechanic's qualifications as a goofball.

RobbieTunes

Classic & Vintage:
Not really classic @shoota, either,.
The OP merely related things a mechanic told him.
A mechanic without motive and apparently privy to tech notices and partner to a carbon frame repairer.

I'm interested in the discussion.

shoota 

Meh, I'm just calling bull, not mad. I'm still the same jovial guy. I just don't see how a leg draped over a top tube can crack it. That seems ridiculous. Right?

bikeaddiction1

Good point, something I had not considered.

RobbieTunes

It does, but have you seen guys treating it like it was a lawn chair, rocking back and forth? No idea if that breaks them or not.

My guess is transportation damage. I have followed some really bouncing bikes on bike racks.

My guess is also that if a tubeless rim splits under that kind of pressure, it may just be a symptom of a design or production defect.
After all, spokes have been used for a long time, but there are still rims out there that crack around the spoke holes.

repechage

Ever seen a sunscreen MSDS? (material safety data sheet) And people put this on porous skin?
Scary. Cover up instead.

repechage

my guess is that tubeless with disc brakes might be less of an issue with rims cracking at the tire seal region.

79pmooney

Carbon fibers's strongest asset is its incredible strength when stretched/compressed along the fiber. But that means a minimum weight structure has little strength when stressed in other directions. So, if you built a truly minimum weight frame, you could easily leave out the extra material required for the rider to use the top tube as a lawn chair before the race starts. Maybe not account for a really tight rim grab with a brake caliper,instead focusing on longitudinal fibers that will be strong and stiff for high bending strength for a stiff wheel. (That photo of the crack along the center of the rim web in the photo above perhaps. Or maybe that crack came from too much pressure, perhaps along with resin weakening from a hard, hot descent with rim brakes.)

(I've witnessed the "top tube lawn chair" many times. That's been happening as long as bikes have been raced.)

Ben

Reynolds 

But are there any aircraft where all the major structural parts are carbon fiber, like in bikes?

canklecat

I have just enough room for an orphaned Domane or Roubaix, if anyone is worried their bikes might asplode. Tubeless accepted. I'll take my chances. Just slip it through the night drop. Mum's the word. No one will be the wiser.

Just don't tell my steel bikes. Tears are salty. They might rust.

RiddleOfSteel

Well played.

I think similarly. Late '90s and early '00s models are well on their way to becoming "just old bikes" with stuff from around 2010-2012 not far behind. Not the cheap stuff either. I am looking forward to scooping up 'yesterday's lightest carbon bike [frame]' for dirt cheap and riding it. My only hurdle is an aesthetic one. Specialized frames have all their tubes arch/banana and in the 61-64cm sizes it looks ungainly. Pinarello's Dogma and other models look similarly bad in super tall sizes, squiggly fork blades notwithstanding. Trek generally does a good job, well, at least with the Emonda. Older Madones with similarly straight-ish tubing fare pretty well, too. Cervelos are solid. Cannondale, goes without saying. And the SuperSix Evos are getting cheaper. Still, though, makes one long for and appreciate a good solid straight horizontal top tube. It lines up with the ground, which never looks bad, and it's lack of slope in either direction, to me, says it's not afraid to be that size, whether short or tall. It's a confident look. Good thing I have a bunch of bikes like that, eh?

Lascauxcaveman 

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?

radroad

The damage isn't from the weight of your leg, it's the methane from uranus.

avole

If you know your aviation history, you'll know that, for many years, including WW1, aircraft used wooden frames with doped fabric skins. This went out when aluminium became available and was used for skins and frames, although certainly in WW2 some aircraft still used doped fabric, while others experimented with plywood, though that was an austerity measure. Aluminium is still very much in use, but CF is running it close in newer designs, especially as fuel efficiency is required.

I can't help thinking that the stresses on, say, a 787 are much higher during take-off and landing than for a bike during its lifetime. Yes, I know there are many luddites who, were they aircraft engineers, would still have us travelling in HP 42s, but, hey, life moves on. It is the same with bikes. Perhaps the problem is not the material, but with the average cyclist's understanding of it.

Johno59

I inspect carbon fiber composite material for a living utilizing nuclear radiation emitting cell examination and color spectrometry. The fact of the matter is military spec - jet fighters, missiles etc is lower than commercial aerospace - Boeing, Airbus etc is lower than sporting equipment it in turn is lower than automotive which is the highest . It is to do with any lunatic can drive a car anywhere in any state whereas pilots are highly trained and planes operate in highly controlled environments.
It may seem counter intuitive but ICBMs have the lowest spec. Probably to do with MAD and WW 4 will be fought by the few survivors with sticks and stones .
To be honest I'm not certain regards bike spec but it and aerospace spec are in a different league to automotive . In fact a plant that makes aerospace spec would probably find the level demanded by automotive impossible. You'd have to have a completely different facility.
Commercial aircraft composition is fast approaching military aircraft composition in being 60 % carbon composite. 15 years ago it was 10%. Many folks who work in the composite aerospace industry find commercial flying to be more and more unnerving as the trend continues up and up.
​​​​​

Bikerider007

I sit to one side on my top tube all the time at rests. But not on carbon. Sounds like I may have a prob if it were as it's probably not designed to hold up in that direction.

jamesdak 

Nope, I never do it. Nor do I sit on the top tube and almost all my bikes are steel.

shoota 

lol

delbiker1 

The leg resting on top tube and causing damage due to stress is, IMO, a bit far fetched. It just makes no sense. All the tubes of a bicycles go through much more stress just in normal riding, sprinting, turning, braking, etc.

delbiker1 

Now this gives a different perspective on the " problem ".

bikeaddiction1

Yes:
://www.compositesworld.com/articles/boeing-sets-pace-for-composite-usage-in-large-civil-aircraft