OldPilot

Commercial airplanes due use kevlar wing spars (generally), the wing spars are designed to take more stress than a normal operation envelope. Basically the wing spar is over designed for a margin of safety, this gives the pilots' that extra margin for emergency situations. Bicycle CF frames are designed to be light, responsive & stiff, correct? I was curious about CF bikes strength/durability after seeing a thread showing bikes with CF failures, mostly at the headtube/downtube area.

I guess if CF bikes were dangerous bike manufactures wouldn't make/sale the bikes & you would hear about all the lawsuits. When you shop for a CF bike how do you discern a quality frame from junk?

jbhowat

Aluminum and steel (and Ti and Mg) bikes fail and the head tube as well - it happens when you push the bike past the forces it was designed for (you crash or hit something HARD).

BillyD

I wish I had time to read through this whole thread. But I don't, so I'll just jump in here.

I just love these bike frame material squabbles. It's always so entertaining to watch the carbon zealots as they frantically try to convince the world that carbon is as durable as any other bike material.

It isn't.

Sure all bike materials will eventually fail . . . ALL ! But carbon fails easier than the rest. It's less durable than the rest. And it can tolerate less abuse than the rest. To argue otherwise is to insult our intelligence. Please stop.

waterrockets 

To rope all frames into four categories based on their material is silly. I think the wrong blow to the top tube would destroy a CAAD9 before a Ridley Noah. It's just too thin.

One thing to note, CF is cheaper to repair than any other material, and everything that's not a major joint separation is pretty easy to repair well.

...I say as I prepare to enter race season on 9-year-old steel...

Velo Vol 

Yes, please do. There's not much intelligence left to insult.

KiddSisko

I'm surprised no one replied to this very good question. Actually, the topic has been discussed here many times, so maybe fatigue is the reason why no reply. Try a search on the topic if you want the complete saga. In general though, price is often the key determining factor. There, I said it. Also, reputable name brands, those companies who have been in the business for over a decade who's good name is as much a part of their ongoing success. Another consideration is recent frame materials and construction methods bring with them the benefit of knowing what to avoid based on past mistakes.

Pedaleur

It just happened to a friend of mine. Dropped his chain, scraped away some coating, and dug a little hole in the carbon. He's looking for repairs shops.

Sorry, no pics.

patentcad

Yes.

patentcad

But of course it's worth it.

tntyz

Is this the case under all conditions? I really only need a frame that's tough enough (with safety margin) to support my style of riding. I'm thinking that a crash that f's my frame, no matter what material, is going to do even worse to my body. And if my CF frame lasts 10 years, then I'll probably be in the market for something new anyway.

jbhowat

That's simply not true. I've seen aluminum frames dent from falling a couple of inches from the saddle to the top tube when resting against a sign post. I guess to be fair you would have to compare frames of similar weights and stiffness of all materials - a normal cycling crash/impact that is bad enough to damage carbon is going to damage any frame material. Quite frankly, I'm more comfortable riding a monocoque carbon frame where there is essentially NO junction between tubes, they are all one piece. On AL and TI bikes you're relying on a very tiny weld. I've also heard of several Titanium bikes cracking at those welds, and of course it happens to aluminum.

I ride an aluminum bike, by the way - but would (and might soon) if it was affordable. You simply can't match the weight and stiffness of carbon. I've ridden high end Ti frames that were flexier than cheap steel. The only carbon frames I've ridden that were that flexy weighed like half as much.

merlinextraligh

From my anecdotal experience, I'd agree the CAAD 9 is more likely to fail. Wife's CAAD7 (with tubes a little thicker even) suffered a fatal dent to the TT from the bike falling over in the garage, and striking a metal christmas tree stand.

The extremely thin walls on on certain portions of an oversized AL tube frame are much more prone to damage than a typical CF frame.

logdrum

Saying I have ridden this and that material is not the same as owning them for a while. I rode a Colnago Carbon the other day and yes I thought it was crap but is it because I have envy or I need more time.

I have bikes made of ti, steel, aluminum and carbon. Carbon is the best climbing bike even though the bike is only 2.5 lighter.

When I was building the carbon bike, I dropped the frame and the seatpost collar took the impact. Nothing happened and it was about 4 feet unto concrete. Alu or steel may have been dented. Also I overtightened the Chris King (supposedly the toughest) lower bearing cup unto my ti frame. You can see that the headset (made of alu gave and not the ti head tube. So much for ti being soft. The thing is that frame was 1250 grams.

Just for grins I ran over the extra carbon fiber seatpost with my car and nothing happened.

silversx80

Methinks that somebody doesn't know their butt from a hole in the wall when it comes to materials.


Quick hint: I can build a frame out of balsa wood and super glue that is tougher than your Ti frame.

4cmd3

This thread is still better than reading about 'cross any day...

bretthammy

Good idea. Increase life insurance too. I'm pretty sure madones top tubes end up impaling 90% of their riders within the first year. By year 3 survival rate drops to zero. You have been warned.

rschleicher

One potential negative of aluminum as a material is that it is subject to fatigue, over long periods of cyclic (no pun intended) stress. With steel, carbon, and titanium, for that matter, stresses that stay reasonably below the failure strength of the tube (or weld, or joint) will not weaken the tube or joint over time. But with aluminum, repeated safe stresses can still result in a slow degradation in the failure strength, due to fatigue.

In practice, this means that the aluminum frame designer needs to over-design the frame to allow for some level of fatigue over time. It might also mean that a very light aluminum frame, without as much design margin, would have a finite lifetime. (Whereas the other materials can retain their designed strength for very long periods.)

As a totally irrelevant aside, my company makes small micro-mirrors (a form of MEMS), that are basically etched out of single-crystalline silicon. This material is extremely non-ductile - at normal size scales it seems perfectly rigid. But we etch into our little micro-mirrors tiny torsion beams that are on the order of 150 um (a um is one thousandth of a millimeter) long, by 20 um wide, by 2 um thick (think of a 10 foot length of 2x12 lumber, only much smaller!). These torsion beams are twisted over a range of +/- 7 degrees. To prove (to our customers) that these devices aren't subject to material fatigue, we have cycled them over 10 billion full-deflection "twists". (To put this into perspective, we flex them 500 times a second, which equates to 43 million flexes a day, and it still takes us almost 8 months to rack up the 10 billion cycles.) Essentially, there is zero fatigue with this material.

bretthammy

So...make me a bike that will last for-ev-er out of it please.

jbhowat

I'd say that as long as you don't crash, a carbon bike will last forever.