daviddavieboy

In the early days of carbon I could see this happening but I think that there is a very good grasp of the material now. FWIW I sit my fat a$$ on the top tubes all tie time and haven't broken my 12' supersix. Mind you I am only 220lbs.

noglider 

Good point, @lostarchitect. Very rational people hold a few beliefs like that. I know I've held some. I probably still do, and I hope I am disabused of them eventually.

Johno59

One of difficult realities to anticipate when CF failure is concerned is the pressure spike of a sharp projectile/object striking CF. If the offending entity has a hard sharp point that strikes the surface of the CF and that tiny point exceeds the yield strength of material the monocurque nature of CF can result in the shock causing the adjoining structure turns to a fur ball.

After the space shuttle re-entry disaster it was discovered heat entered the wheel bay of the wing via the CF leading edge of the wing and this ingress subsequently destroyed the vehicle.
The chicken cannon was deployed to reaffirm the integrity of the leading edge. As expected the high velocity chickens comfortably bounced off the leading edge of the wing.
Someone suggested the insulation seen falling off the main fuel tank and striking the wing's leading edge during lift off might have been frozen. The chickens were subsequently frozen and to everyone's horror the frozen chickens comfortly punched thru the wings CF leading edge.
CF can handle astonishing loads way beyond any other materials. When it comes to sharp pointed loads like a handle bar end, a sharp piece of flying flint, a falling bike striking a pedal axle, chainring, chunks of frozen insulation or a frozen chicken beak the potential for unexpected catastrophic failure is much more complex and unpredictable.

RobbieTunes

Now I'm afraid of chickens.

RobbieTunes

This could be solved easily at RAGBRAI. (As if a "solution" was needed).

Find 100 cyclists on steel.
Find 100 cyclists on aluminum.
Find 100 cyclists on carbon.
Let's leave titanium out of this.

At the halfway mark, each bike will have a cinder block dropped from 4' above it, directly onto the TT. Participants must ride the bike, damaged or not, to the finish.

Or skip the whole mess and just ride bikes.

crank_addict

I've watched this vid a few times, made by Joe Graney - Santa Cruz

squirtdad

only frozen shot by cannons should be of worry.......but my last crash was because my neighbors fat/solid dog ran in front of me cashing a cat.... so I am very careful passing dogs

crank_addict

Its NOT the makeup or carbon fiber material and resins, its how its put together, number of layers, directional weave, etc. applied for intended application.

Hopefully some of you naysayers watched near the end of Joe Graney's vid.

In comparison the best steel bike frame with that bashing would be butter bat.

Johno59

If you are very fit and very strong a CF bike will leave every other made bike in your wake, regardless whether it be on a track or on a 3000 km tour.
f you are neither fit nor strong the added cost and reduced comfort makes little sense.
These characteristics still appeal to an amateur for aspirational reasons but if you foolishly lend your bike to anyone or allow it to fall over, whether you are mounted on it or it merely fell over in the bike park, the rationality vi's a vi's steel makes even less sense.
​​​​​​

squirtdad

no question....now lets do that with a high end carbon road bike, not a well engineered mountain bike

RobbieTunes

I wish I understood that.

Johno59

If you could duplicate the same power under the same conditions on a carbon bike and then a steel /ally bike at say 20 % of your best there would not much difference in distance travelled. If you put in 100 % on all three the CF bike would travel further coz the frame transfers power more efficiently.

Pros can generate 300 Watts for hours, sprinters get over 1200 Watts at the end. At over 25 mph very strong very fit people can extract the performance dividend CF offers that steel simply doesn't possess.
I drafted a guy yesterday on my 40 yo steel flat pedal winter hack. We sat on 25 mph into a headwind
His bike full carbon, disc brakes electronic shifters and a crank power meter. My bike cost 50 bucks his near enough to 10,000 dollars . All good you might say but by wheel sucking I needed only half the power he was putting into the road. If we'd swapped bikes I doubt he'd be able to keep up that speed on point for very long and if so he'd need considerably more power.
If you lend your CF bike and it gets a bad knock you might not know it until it begins to delaminate and go mushy hundreds of miles later when you are giving it all the berries.
In aircraft one compelling reason they didn't build fuselages from CF up until now was if ground equipment ie stairs, fuel trucks, baggage conveyors etc hit the hull CF wouldn't ding like an Ally skin that received the same impact. In other words if you are the sole user of your CF bike you are fully aware if any damage has occurred, especially the knocks that leave no discernable sign on the surface.
In the video the whacking of the CF frame would not become a structural problem for a thousand miles later whereas the metal frames were obviously kaput.
Some might argue clear evidence of damage is the safer option. Having examined much damaged CF that records indicate nothing untoward had ever occurred in the failed area I am very sceptical of what people choose to admit to. As such I would jealously guard any expensive CF frame I owned like a complete *******.

daviddavieboy

Did you have to Drope the hamer?

Seriously though I understand what you mean. I have noticed though my w/kg is higher using one of my old steel bikes compared to the carbon bike in group rides but I think that is only because of greater effort to get the same speed.

jamesdak 

Totally not buying this.

RobbieTunes

I was joking. I have some experience.


I've fixed a few carbon bikes that were a-loaned out (lent?), b-had the seat post raised up from the "bottomed out" requirement and then c-fell over. When the saddle hit the ground, leverage and movement prevailed, cracking not only the seat tube, but the aluminum liner for the seatpost, too.

As far as the other stuff, doesn't really matter to me. I've drafted plenty of carbon commandos, and they've drafted me. I've descended past many, many carbon bikes because I just don't feel they had the confidence to let it go. A bit heavier bike on the descents seems to be a confidence-builder. I've climbed past many, and they've climbed past me. They're all bikes.

I don't have the power to worry about some miniscule advantage of transfer at max effort.

After winning the TdF 29 times in my mind, just not my priority.

Your 100% right-don't lend you high-dollar carbon bike out to anyone. They are pretty susceptible to all kinds of damage when not being ridden, and those without a personal investment in the bike don't always have a built-in incentive to avoid that.

ljsense

I've rested my full body weight minus my left leg on all my carbon bikes whenever I'm sitting out a stoplight or waiting for a race to start, someone to finish their coffee, or whatever. It's comfortable and, like that post above, it was modeled by the pros. Now I can never really enjoy it in the same carefree manner again. Thanks.

As for the other part, I did break a carbon clincher rim running tubeless -- just hit a really huge pothole with a sharp edge on the far side, tire burped out its air, rim cracked. I think tubes make more sense for tires less than 700x28 or, better yet, tubular.

Johno59

At half gas CF,, Steel and Al are all pretty rigid. The bottom bracket stays pretty still and most of the power from your pedals goes into the drive train and this power goes into the rubber hitting the road. As you crank up to full gas the bottom of the frames start to flex from side to side. This lateral movement absorbs power. Pedalling in circles rather than squares helps reduce this swing but CFs greater rigidity reduces the power bleeding into the frame more than the others.
We are talking power levels on the cranks by legs that cruise above 25 mph for hours on end for fun. In other words if you go 25 miles under 50 minutes these properties are important - for the rest of us they amount to next to nothing.

ljsense

I've heard this frequently and forever -- the idea that some amount of power vanishes into frame flex, and a stiffer frame would put more energy into the rear wheel. The energy used to flex the frame, though, is released when the frame unflexes -- it doesn't just disappear or get turned into heat or sound. And as the frame unflexes, it actually applies force to the drivetrain. GCN did a feature where they demonstrated that a frame unflexing drives the chain forward, spinning the rear wheel.

It's worth checking out: https://thebicycleacademy.org/blogs/...lex-gcn-tech-1

Johno59

The unflexing energy can go anywhere. Some of it may even go up your backside, hands, or even the rear wheel. One thing for sure going straight into the drive train from the pedals has to be the most efficient path.
But your genersl point is correct, the advantages are miniscule and only exert themselves at the elite level.

crank_addict

RobbieTunes

Hope the post didn't ruin the mojo!


BTW, are you aware of the Coppi birthday party? September, in Hollandale, PM me for details....

dddd

I've seen what appeared to be longitudinal cracks at the top surface of the toptube on at least three monocoque carbon frames over the last ten years.
This on bikes still in service. At least one was a Cannondale as I recall.

I don't know what caused the cracks, but I've seen similar longitudinal cracks along the back side of a few carbon seatposts, near the clamp, a place where inward force is being applied to the tube.
So if a toptube isn't designed with sitting (literally on one's sit bones) in mind, I could see such a failure resulting from this on a lightweight carbon frame.
I sit on a bike's toptube often enough, such as when resting tired legs at a rest stop. Just like a stool or like sitting on a railing, etc. Very common to see.

I agree with the mechanic on what I think he was trying to say (that such failures aren't seen on metal toptubes).

squirtdad

now lets do that with say a ~800 gram frame (1 lb 16 oz) (which is less than the weight of a full water bottle) https://www.bmc-switzerland.com/us-e...lr01_disc-ltd/

52telecaster

Thankfully i wont have to worry about any of this. Being a slow tourist has its advantages!

crank_addict

Kids on juice these days .....