What is the difference between threaded and threadless forks? Unlike a threaded headset, a wireless headset does not have a threaded upper headset race or use a threaded head tube. Instead, the steerer tube extends from the fork through the steerer tube and over the headset, and is held in place by the tight-fitting stem on top.
Can I use a threaded fork with a wireless headset? It is a very bad idea to install a threadless headset so that the handlebar stem is supported by the threads of a threaded fork. You can install a threadless headset on a threaded fork, if the steerer tube is high enough and you use a bushing stem. Threads must terminate above the top race of the helmet.
What is the difference between threaded and non-threaded forks? The threadless fork is easier to store because it can have fewer sizes, it can be cut to fit the bike. While the threaded fork must be cut to size, or rather made to size. This therefore makes it cheaper to store threadless forks.
Can you replace the threaded fork with Threadless? It’s possible. You just need to remove the old bearings and get a complete new headset for the frame. You then treat it as you would any wireless system. Note, it is possible to do this without replacing the current headset, but this requires knowing exactly what top travel and seals you would need.
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Theres a page on here explaining the basics, Terminology index – a list of bike part names and cycling concepts
There are some advantages for maintenance, it is simpler and faster to adjust the bearing preload with the central bolt through the top cap, rather than using the lockrings on a threaded headset. Threadless also requires only hex keys to adjust, as opposed to specific lockring spanners.
The overall system of threadless headset and clamp on stem is probably lighter and stiffer, but Im guessing… if true its a big reason! i.e. lighter weight and better steering.
The larger stem with threadless headset allows material for the modern handlebar clamp with four bolts, enabling you to remove the whole handlebar assembly easily. It is able to achieve this without significant weight penalty. With a lot of quill stem designs, the clamp forces you to remove brake levers etc from the bar to remove the bar from the stem by sliding it through. There are two bolt clamp designs for quill stems but arguably 4 bolt clamps are a superior design.
With threaded, the quill stems have a tendency to get rusted in place, worsened by aluminium vs steel combinations, so rust or galvanic corrosion can prevent removal of the stem, thus adjustment or bearing servicing becomes impossible if a threaded headset is neglected for too long. This is less likely to be a problem with a threadless headset.
Also for threaded steerers, the steerer must be cut to fit the frame head tube and the headset stack height quite accurately. Replacement headsets must match this stack height quite closely to be compatible. Whilst this is an unusual occurrence, more significantly the fork/steerer tube cannot be re-used in a taller head tube on a different bike. Both these issues are more easily managed for a threadless system.
Hope that helps, no doubt theres more reasons than this!
As to the what, others have pointed to other resources.
As to the why.. From all I read it appears to be because of MTBs and the aftermarket fork sales. The threadless fork is easier to stock since it can be fewer sizes, it can be cut to fit the bike. Whereas the threaded fork has to be cut to the correct size, or rather manufactured to that size. Thus this makes it cheaper to stock the threadless forks. It doesnt sound like the right reason 😀 But from all I read, this was the primary reason. There are other reasons that others have pointed out, weight, stiffness etc. I dont like the reason that the larger stem makes it easier to remove the handlebar easier because I feel they could have done that with quills as well.. but that is an advantage for most people.
Another advantage is it is easier to adjust or assemble/disassemble. I spent weeks/months tracking down the right tool to tighten my threaded headset, but threadless are typically fastened with very common hex key size screws.
But I am not convinced of the original reason either because all the cheaper bikes have threaded stems :D. Although it might be that standard designs such as MTB and road are easier to use with the threadless design, whereas the threaded system allows for more variety such as my foldie.
I was curious about this.. because I find the whole adjust the height with spacers concept very hacky. Spacers are typically used in other places to hack stuff that dont otherwise fit after all..
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What is the difference between threaded and threadless forks? – Related issues
A “threadless” stem refers to a system in which a fork with a threadless steerer tube extends through the steerer tube. A stem (A) then clamps around the outside of the steerer tube with spacers (B) if necessary. Finally, a top cap (C) keeps everything in place and acts as a helmet adjustment.
When should I replace my bicycle helmet?
If you’re experiencing play (unwanted movement) in your headset or a rough squealing noise when turning the bars, it’s likely time to service your headset or replace the headset bearings. Most modern bikes use two sealed bearings positioned at the top and bottom of the steerer tube.
FAQ
Can I use a threaded fork with a threadless headset?
Why are threadless stems better?
How do I know if my fork is threaded?
What does threadless fork mean?
