Originally Posted by RoadLight

And you don't think that ride quality is important? It's no "reach" at all.

In the past alloy frames have a well-deserved reputation for poor ride quality (bad mixture of stiffness and vibration damping). And aluminum alloys have a generally bad reputation in all industries regarding stress and fatigue.

A few bike manufacturers have continued to develop their alloy frame design and manufacturing processes and have found ways to mitigate much of the ride quality issues. But such frames are still in the minority and the majority of alloy frames have an undesirable ride quality. Manufacturers have realized this for a long time and the higher-priced alloy frames are typically mated to composite forks to improve the ride quality.

But, short of some amazing metallurgical breakthrough, nothing can be done to improve the fatigue problems of aluminum. This is why alloy frame designers are forced design alloy frames with much higher safety margins than steel or titanium. And this robs alloy frames of much of their potential weight savings since tubes must be so much thicker owing to fatigue and the fact that aluminum is a relatively "soft" metal.

Composite forks are used to overcome the "harsh" ride quality of alloy frames. This has nothing to do with stress failure or fatigue. And most cyclists---including many who "think" they know a lot" are ignorant of composites, what they can do and how they are used. Composites made with carbon and other materials typically suffer from near-zero stress accumulation. Simply put: they do not fatigue! When they are pushed beyond their "breaking" point, they break. But you can push them just short of their breaking point over and over and over again with no weakening of the material. This is untrue for all metals but the levels vary dramatically from one metal to another. This is where aluminum alloys are their weakest because aluminum begins to fatigue at very small stress levels and this fatigue gradually grows over the years even when the stress is very mild. Steel, for example, has no cumulative fatigue at low stress levels---you can push it much harder before stresses begin to accumulate. The same for titanium.

But the unique thing about the composites is that engineers can control the breaking points based on direction and kind. Metals are uniform. Since the composites are not, crafty designers have tried to make the lightest frames possible for racing by designing them with good strength only in the directions needed. They intentionally allowed them to be weak in areas where they would not receive much stress. This is why you cannot use a strong circumferential compressive force on most composite bike tubes---they simply were not designed for it.

But the thing is, if frame designers wanted to make a composite frame that can handle a wider variety of stresses, they could at the expense of weight. This is what they should be doing for consumer frames---but they aren't because many cyclists get it into their head to buy what they see the pros riding without considering that those frames are purpose-built for racing---not general cycling. And another reason they don't is because the high amount of manual labor required to construct a composite frame, keeps their price high and most buyers looking to spend top dollar on a bike want it to be as light as the pro bikes they see being raced.

So, if some enterprising manufacturer wanted to design a composite frame for touring that would have great durability for most situations, they could and it would last longer than any metal frame because there is no practical lifespan limit for most composite materials.

In the future after manufacturers figure out how to fully automate composite frame making, I expect cyclists to be able to order a custom-built composite frame based on their personal design criteria. They'll be able to specify how much strength any part of the frame can handle from a variety of vectors. Composites are the future. But we're still in the stone age of manual labor regarding their manufacture today.

Kind regards, RoadLight