Most of the newest top end bikes are carbon fiber and the latest trends are for lighter and ever lighter bikes. This causes manufacturers to make lighter and lighter frames.
While carbon fiber has higher strength to weight ratio than most other materials it also has its own problems - the thread length of a carbon fiber is short. This means that as the frame resin embrittles with age the frames can fail catastrophically.
Exactly how much of a problem this seems to be is a question since Trek offers a lifetime limited warranty (they replace the frame only). I think that Specialized matches this but I haven't actually found it written anywhere. But Colnago who has more experience with the material than most other companies only offers a 3 year warranty and that only because it is the minimum by law in many states. They state, when asked, that they don't trust them beyond two years, Now I'm not sure I understand this since most of the Colnagos are constructed quite conservatively and not for minimum weights. Virtually all of the top end CF bikes are lighter than Colnago. And the Taiwanese versions (CLX etc.) pioneered the stress management techniques used in Aerospace industries. Is this only self protection? I don't know.
Titanium frames have roughly the same weight as CF plus they are extremely resilient as long as they are welded properly. It is always possible though rare, for the helium envelope that the welding is accomplished under to allow some oxygen in and cause titanium oxide to form in or around a weld. This is a brittle material and generally if you don't find a crack within a month you're safe forever. This is a long lived material.
Aluminum frames also CAN last forever but they began pressing the envelope of weight pretty rapidly so some frame cracks started appearing relatively early. And unlike titanium they can occur at any time over the life of the material. However, it must be noted that these failures are seldom catastrophic. Usually they will begin making odd noises and you will look and discover a broken tube while the others are fine.
Steel bike frame are another matter. By the time they started making very high quality steel tubing at Columbus, Reynolds and others, it was long after WW II and steel had become a science. There was no guesswork in the double and triple butted tubes and only the very occasional manufacturing errors caused these frames to break. What's more, although they give away a small weight penalty, the frame and fork are only a part of the weight of a bicycle so this penalty is relatively small.
At the moment that UCI has a weight restriction on bicycles of approximately 15 lbs and this isn't very far from the very top end steel bikes though even one ounce is now considered extreme on race tracks and in truth only those with a lot of climbing.
So what we're presently seeing in cycling is probably a very bad trend - lightest weight possible which is similar to the latest trend in components which are the largest number of speeds possible. This will cause little more than headaches for the sports/recreational rider. Though some trends are good (tubeless tires) most of the others are not, More speeds means narrower cogs and rings, higher ratio differences with 11-32 cogsets for hard Tour stages and derailleurs now so weak that picking up a rock or wire into your rear derailleur can end your ride. It makes you yearn for the old days of 8 speeds when you could have a gear for every purpose without having to shift two or three times every time you are changing terrain. So maybe manufacturers should be building bikes more for the actual use of a rider rather than getting them to play at racing rather than buying a bike that actually serves a purpose. This is fine for kids but I have ridden in a lot of areas and what I'm seeing is that riders tend to be in the mid 30's and later. Racers are very few but people trying to keep up with them are far too plentiful. And here I am now in the higher age group and most of my riding buddies are dead or having extreme health problems.
I have a good day when I do a metric and average 15 mph. And yet when I did a very large metric with about 2,000 riders in it when I crossed the line I was told that I was the 182nd finisher. And several hundred of the Century riders started an hour before me! Does this sound like people should be worried about maximum performance and only using the lightest and most expensive bikes made? You could get a high quality high quantity manufactured bike made of steel with top line components on it for $2,500 or less vs a $13,000 carbon fiber wonder. If you are in your mid to late 30's that $10,000 in your retirement account can made a huge difference to having a longer and more comfortable retirement on your original bike!
While carbon fiber has higher strength to weight ratio than most other materials it also has its own problems - the thread length of a carbon fiber is short. This means that as the frame resin embrittles with age the frames can fail catastrophically.
Exactly how much of a problem this seems to be is a question since Trek offers a lifetime limited warranty (they replace the frame only). I think that Specialized matches this but I haven't actually found it written anywhere. But Colnago who has more experience with the material than most other companies only offers a 3 year warranty and that only because it is the minimum by law in many states. They state, when asked, that they don't trust them beyond two years, Now I'm not sure I understand this since most of the Colnagos are constructed quite conservatively and not for minimum weights. Virtually all of the top end CF bikes are lighter than Colnago. And the Taiwanese versions (CLX etc.) pioneered the stress management techniques used in Aerospace industries. Is this only self protection? I don't know.
Titanium frames have roughly the same weight as CF plus they are extremely resilient as long as they are welded properly. It is always possible though rare, for the helium envelope that the welding is accomplished under to allow some oxygen in and cause titanium oxide to form in or around a weld. This is a brittle material and generally if you don't find a crack within a month you're safe forever. This is a long lived material.
Aluminum frames also CAN last forever but they began pressing the envelope of weight pretty rapidly so some frame cracks started appearing relatively early. And unlike titanium they can occur at any time over the life of the material. However, it must be noted that these failures are seldom catastrophic. Usually they will begin making odd noises and you will look and discover a broken tube while the others are fine.
Steel bike frame are another matter. By the time they started making very high quality steel tubing at Columbus, Reynolds and others, it was long after WW II and steel had become a science. There was no guesswork in the double and triple butted tubes and only the very occasional manufacturing errors caused these frames to break. What's more, although they give away a small weight penalty, the frame and fork are only a part of the weight of a bicycle so this penalty is relatively small.
At the moment that UCI has a weight restriction on bicycles of approximately 15 lbs and this isn't very far from the very top end steel bikes though even one ounce is now considered extreme on race tracks and in truth only those with a lot of climbing.
So what we're presently seeing in cycling is probably a very bad trend - lightest weight possible which is similar to the latest trend in components which are the largest number of speeds possible. This will cause little more than headaches for the sports/recreational rider. Though some trends are good (tubeless tires) most of the others are not, More speeds means narrower cogs and rings, higher ratio differences with 11-32 cogsets for hard Tour stages and derailleurs now so weak that picking up a rock or wire into your rear derailleur can end your ride. It makes you yearn for the old days of 8 speeds when you could have a gear for every purpose without having to shift two or three times every time you are changing terrain. So maybe manufacturers should be building bikes more for the actual use of a rider rather than getting them to play at racing rather than buying a bike that actually serves a purpose. This is fine for kids but I have ridden in a lot of areas and what I'm seeing is that riders tend to be in the mid 30's and later. Racers are very few but people trying to keep up with them are far too plentiful. And here I am now in the higher age group and most of my riding buddies are dead or having extreme health problems.
I have a good day when I do a metric and average 15 mph. And yet when I did a very large metric with about 2,000 riders in it when I crossed the line I was told that I was the 182nd finisher. And several hundred of the Century riders started an hour before me! Does this sound like people should be worried about maximum performance and only using the lightest and most expensive bikes made? You could get a high quality high quantity manufactured bike made of steel with top line components on it for $2,500 or less vs a $13,000 carbon fiber wonder. If you are in your mid to late 30's that $10,000 in your retirement account can made a huge difference to having a longer and more comfortable retirement on your original bike!