ReneV

"Truly".

1500SLR

So now you can't debate the argument with logic and start with the semantics... semantics is one of the lowest form of arguments. They lead to equivocation rather than debating the actual content in context.

ReneV

I see we have any number of comprehension issues in play here. I am stating clearly that you keep moving the goal posts in what you say.

1500SLR

No we don't have a comprehension issue here at all. Its clear to me you didn't read the article I gave you on fracture toughness. We are talking about bicycle frames not carbon rods by the way. To deal with carbon in the context of all the ways a bicycle frame could be built we have to deal with the realities of fracture toughness. Compressive failures where alloys become plastic are actually all kinds of irrelevant to bicycle frames. In the vast majority of cases you will never reach the point on an alloy frame (steel is also an alloy) where you will reach the point where it becomes plastic. Even if you do the frame will bend rather than crack which is almost always entirely more survivable for bike frames.

The common and popular misconception is that materials that bend are "weak." It is based on the misconception that those materials that do no not bend are "strong". In reality, many materials that undergo large elastic and plastic deformations, such as steel, are able to absorb stresses that would cause brittle failures in materials such as carbon and glass. You've been run over by the carbon hype train.

ReneV

The Cinelli XCr frame you mentioned earlier is listed as weighing 1,560g on the manufacturer's product web-page.
The Trek Emonda SLR frame is commonly quoted as weighing 640g.

What parts of this are hype? What parts are not based in reality?

1500SLR

The argument was that "carbon is stronger than steel." In fact, we should be more worried about whether a bike is prone to brittle failures. But people who continue to push the fact that carbon is stronger than steel continue to rely upon plastic failures. They also ignore the constant stream of brittle failures, even those that pop up on this forum repeatedly.

As to your question explicitly... The weight of a frame is only one factor among many. I already raised the point that you can make a 6.7kg bike out of steel, you can also make one out of aluminum, or titanium. You have to take into account all of the components of a bike not just the weight of the frame itself.

phtomita

seau grateau

Carbon is dumb and if your bike is over 14lbs you're not even trying.

Kimmo

When I say carbon is stronger than steel, I'm talking about riding the damn thing, not crashing it - this is why a carbon frame weighs like 60% of a steel frame - because it's stronger stuff. You're thinking of a property better described as toughness. By the way, it's said that carbon's fatigue life is practically infinite.

And there's no way in hell tube profiling and mucking around with wall thickness can match what you can do with carbon in terms of stiffness and compliance in various directions.

This shouldn't be that hard to understand.

PS. My TCR cost $40 after I sold the groupset off it.

1500SLR

Then we have to accept that crashes are inevitable. I've been driving for over almost 20years. In the space of that I'd never had accident until a couple weeks ago. For whatever reason a series of unfortunate events happened. A car came to a complete stop after another car was involved in an incident where they swerved in front of the driver ahead of me, before you know it you have a pile up. On a bike especially in racing conditions accidents happen nearly every stage of a race. In crit racing it happens almost every race.

We can accept that carbon has an almost infinite life if its put in a vacuum avoiding all other facts but we don't live in vacuums. If you accept the fact that you're going to be spending money breaking bike components inevitably. That's fine also. Not all of us have a bottomless put of money to spend on a shiny new bike frame every time something happens even if its not our fault.

HTupolev

While it's true that crashes usually need to be very extreme to fracture steel frames, the yield strength of steel frames is usually not particularly good. And while it's not that dangerous to bend a slightly-deformed Varsity frameset back into shape, higher-end steels and thinner-wall tubes make the matter much sketchier. In the case of some supersteels like Reynolds 953, framebuilders even have to plan their process carefully to avoid post-weld alignment cold setting.

I mostly ride steel bikes, but crash resilience has nothing to do with it.

The anisotropic strength of carbon is the root of both benefits. As to which one is more "primary", there really isn't enough readily-available information to say, since the actual effects of frame flex and stiffness are not particularly well-understood, at least on the public stage. I was shocked last summer when Cannondale let one of their engineers go and semi-agree with Jan Heine.

1500SLR

I never really said anything about bending a bike back into shape . I was talking about the problems that are involved in relatively common bike crashes and frame failures. Actually, the primary concern with steel and aluminum frames isn't even whether they will bend. You will likely break a weld before you bend anything seriously. On the other hand a brittle failure happens rapidly, it may even happen as a result of you dropping your bike and it may well cost you your life if you keep riding on it. These are all facts.

Its good to talk about all the other benefits of carbon in a perfect vacuum, bu they don't represent the reality of riding a bike and some people choose to be ignorant of the facts that accidents do happen even if its detrimental to their own benefits to understand.

znomit

1500SLR

Carbon... but yeah... Its had a pretty damn easy life. 2owners and about 6000miles. That's exactly what I'm worried about especially with older carbon bikes. The forks assploding and killing the rider as a result. You can't really tell if your bike has cracks in it or not either unless you trust your own riding history.

Kimmo

Yeah, it's hard to test this stuff, for sure. I wonder if having a special frame with a downtube a bit like one end of an adjustable swaybar would help...

Anyway, if some flex is advantageous, I suspect you want less of it in a carbon frame than a steel one, because hysteresis.

themidge

Back on topic, for road bikes this is what I think:
>12kg is mega heavy
>10kg (most cheap stock bikes) is pretty heavy
>8kg (midrange stock) is a bit porky still
>6.8kg (higher end stock bikes and easy to achieve when building up your own) is pretty good and definitely 'light', some pro bikes are like 7.5kg
<6.8kg, technically 'illegal' so definitely light, but nothing particularly special
<6kg (very high end stock, still easy to build up but getting expensive) is very light
<5kg (a select few stock bikes, and difficult to build up without vast expense and/or tuning) super light, and probably not suitable for heavy people
<4kg (no stock bikes I've heard of, requires customisation and lots of money!) ultralight.
The lightest bike in the world weighs 2.7kg and cost an estimated $45,000, not a single part can be bought as it appears on the bike 'off the shelf'.
IMO any road racing (whether you race or not) bike over 8kg is unnecessary heavy. So many people spend thousands on fancy custom bikes, and I'm often amazed at how much some of them weigh, even with top end everything! Of course it doesn't reeely matter how much your bike weighs, but it's so easy to build a light one so why wouldn't you?
My bike weighs 7.3kg, which I do not consider to be particularly light and would like to improve on.

Bah Humbug

If you call it art, it's art.

Kimmo

Damn straight.

Also, technology = culture.

woodcraft

Your mean like your 1500SLR?

When you dent the top tube of your aluminum frame, it's junk.

A carbon frame can be readily repaired.

1500SLR

No not really, you can repair aluminum just like any other material. Carbon doesn't dent it cracks, and that's my point. It cracks and a lot of a time you don't know its cracked until it snaps and at which point it may kill you. You are more likely to break a weld than dent an alloy bike anyway.

Pizzaiolo Americano 

1500SLR

I'm not playing this game.

Kimmo

If it's 6xxx-series ally, it should be heat-treated after the repair; pretty sure nobody offers such a service.

The fact is, there are mobs doing proper repairs to carbon frames, and that pretty much doesn't happen with ally.

LOL, cause you know that's fail by hypocrisy?

Pizzaiolo Americano 

Kimmo

Not so much if you've spent a bunch of energy slagging off carbon, methinks