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Threaded bottom brackets

  • are much simpler to install
  • require minimal tools (press-in requires a $300 press)
  • are automatically aligned, as the thread was cut in the factory.

So what is the reason not to exist headsets, the cups of which thread into the headtube? And be the most often used ones?

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Note that a lot of high-end mountain bikes are moving to a press-fit bottom bracket. I'm not the right person to tell you why, though :) –  Olly Hodgson Oct 11 '13 at 10:38
    
I've been wondering the same thing. It seems to me to be needless change for change's sake -- a selling point, but actually complicating bike fitting. –  Daniel R Hicks Oct 11 '13 at 11:50
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There used to be threaded headsets. However I think they have fallen out of fashion. Perhaps they had a tendency to become loose, which would be catastrophic, as you would no longer be able to steer, or your front fork could disengage. Compared to your bottom bracket cups coming lose, which would just cause problems with providing power to the bike (cranks would still be connected to the bottom bracket). Also properly designed (not Italian), they are self tightening, and won't ever come loose, for the most part. –  Kibbee Oct 11 '13 at 12:48
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@Kibbee, I think those still use pressed-in cups. No? –  Vorac Oct 11 '13 at 13:10
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@Kibbee - I've seen threaded headsets loose to the point that the balls were falling out, and they did not catastrophically fail or cause an inability to steer (other than being simply more difficult). And I cannot imagine how a loose headset could possibly cause a fork to "disengage". The threadless headsets seem more prone to catastrophic failure. –  Daniel R Hicks Oct 11 '13 at 14:57

1 Answer 1

up vote 3 down vote accepted

The cranks are always spun in the same direction and the threads are located so the cups don't get loose.

The headset does not have a direction where the spinning is happening and it is not possible to have self-tighning cups.

Also fork gives vertical load, directed into the threads. Also there is a big frontal load on the fork which will be transferred into single directional side-load on a thread. A thread can cope with each of these factors separately, but both of these, combined with constant vibrating, will eventually cause the thread to fail, especially in aluminium frame.

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But the torque on a headset cup is vanishingly small, compared to other rotating parts on a bike. The locknut on top is more than sufficient to prevent loosening if properly installed. And there's certainly "side-load" on a bottom bracket. I can see, however, the argument that aluminum bikes have a problem with the threads, and, since we must always driven to use the least common denominator, steel bikes end up with the short end of the stick. –  Daniel R Hicks Oct 14 '13 at 22:08
    
@DanielRHicks It is only theories I've came up with. I really don't know why the industry gone with the current set up. –  trailmax Oct 15 '13 at 9:24
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Additionally, threading is expensive to manufacture and involves an extra process step. –  Byron Ross Oct 15 '13 at 20:57

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