threaded and threadless fork origin

Question

I was wondering why for a relatively long time the most common fork set-up was the threaded + quill stem one. Why?

• To me, it makes sense to try to have one point of failure for the the steering system of a bike (handlebar and fork), but it does not seem appropriate that said point of failure is hidden, requiring the disassembling of parts of the bike to be checked for its conditions.
• From the fork manufacturing point of view, threaded and threadless fork still share the design of the 2 tubes down and 1 tube coming up, with the possible failure at the connection between the two parts, so I see no reason for making the top part "shorter" and then having a stem reaching down into it to connect.

This question states that threaded stem are stronger, but the "test"[a] does not convince to me as being reliable.

I reserve myself to put here the answer, if I find something useful in the next weeks/months.

[a] holding the front wheel between your feet and checking if you can turn the handlebar without turning the fork ...

Answer 1

Most bicycle part designs get at least tinkered with fairly early once materials science is sufficient to enable them. Here is a picture from Terashima's The Data Book of a threadless headset from 1952:

The question you ask weaves together technological, cultural, and regulatory elements. It would be difficult to come up with an answer that isn't conjecture and doing so would probably be a good topic for a graduate project in industrial history. Threaded favors the type of upper body position that utilitarian cyclists favor (the vast majority of cyclists in the world, especially for most of the last cenutry). Getting to the same type of upright positions with threadless is possible, but takes contrivance. The adjustability and ease of making major position changes offered by threaded is also a boon to utilitarian cyclists, while the weight savings of threadless are of little functional benefit even if they are welcome.

Why the change didn't happen en masse earlier on performance bikes is an interesting question. Cultural and commercial inertia can be powerful forces in that world. A dynamic to consider is what degree of risk has to be accepted by the first companies to make and market a particular new standard. Threadless does succeed at giving performance-oriented and/or strong riders a marginal gain, but for manufacturers and brands, the benefit of offering that has to be weighed against the risk of being rejected by dealers or the public. In the bike industry there are often a group of people who have their eyes open to the direction things could go once the value and risk proposition looks attractive enough, but who also have strong impetus to stay the course and make conservative decisions so their companies stay in the black that year.

Answer 2

The threaded design is good enough. Sure it is heavier than necessary, flexy, has the single point of failure, the stem can seize in head tube, it is more expensive to manufacture and requires special wrenches to adjust, but none of these problems is exactly a showstopper. On the other hand, it has the benefit that the height can be easily adjusted until the stem is stuck.

For a long time there was no strong incentive to invent a different system, but when threadless headsets were invented, they quickly took over the market.

Answer 3

It depends what you mean by "a relatively long time". You're looking to compare one against the other, but that is only possible now they both exist. The threadless headset was patented in 1990. So for the 100 years of safety bicycles before that point, there was no comparison to make.

Once it had been invented, it was quickly adopted by the world's bicycle manufacturers. It may not be superior in every way, but things rarely are.

For a timescale on the changeover period, I give you the 1999 Specialized Allez, which adopted a threadless stem over the previous year's threaded. I regard Specialized as relatively responsive to cycling trends and it took about 9 years to see this innovation arrive on one of their mainstream, base model, road bikes. Threadless headsets are now effectively ubiquitous on all kinds of bicycle.

In the grand scheme of things, ten years or so for this system to become widely adopted isn't such a long time.

Answer 4

This seems like a good history of the Aheadset, the first successful threadless headset that I know of. The advent of mountain bikes uncorked a lot of new ideas in cycling, this being only one. A lot of those ideas caught on because they reduced the cost of manufacturing, as is true of this. As mentioned in this thread, threadless systems are worse than quill stems in terms of adjustability, and I would speculate that adjustability wasn't seen as such a big deal on mountain bikes at the time.

Another thing that probably cemented its popularity is carbon forks, which started to catch on around the same time. Early carbon forks usually had aluminum steerer tubes; better carbon forks these days usually have carbon steerers (I know of one company that sells some carbon forks with steel steerers). In either case, those are not good materials to cut threads into, so in order for carbon forks to take hold on road bikes, a threadless system would be a prerequisite.

Answer 5

In a word - tradition.

A bike looks like a bike because that's what bikes look like. Quill stems and threaded headsets endured for so long as the normal will be at least partly because of this.

I was going to say that manufacturing requirements contribute, but the argument doesn't stack up for forks where the steerer length is either trimmed at install, or hidden by the top cap.

In short, Cycling suffers from a boat-anchor of "that's the way we always did it" compounded by UCI regulations mandating what bikes look like.