Tube on top of headset... purpose?

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simonineaston
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Tube on top of headset... purpose?

Post by simonineaston »

What's this tube thing on top of the actual headset? It looks nice, but what's it for?
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AM speed bar arrangement #3
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531colin
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Re: Tube on top of headset... purpose?

Post by 531colin »

It looks like this thing https://www.bing.com/images/search?view ... ajaxhist=0
But taken to the Nth degree.
I never liked the Stronglight thing....the idea was you could fit the quill stem higher, because the extended top nut covered the "max" mark on the stem. Does it support the stem properly? who knows.
Would that great long tube which is held only by a few threads support the stem properly? I wouldn't trust it!
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NATURAL ANKLING
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Re: Tube on top of headset... purpose?

Post by NATURAL ANKLING »

Hi,
Its looks like a steerer extender.
As that is a lock nut on the top.
Raises the steerer without having a long head stock tube.
So you can use a standard stem!
To be good it would need the coloured tube between the nuts on the steerer to be a snug fit on the external diameter of the top portion of the steerer tube!

P.S. Brucey would probably scream at that device!
Although in favour the steerer tube is not extended with an addition part just supported by the additional tube from distortion by the stem wedge.
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Norman H
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Re: Tube on top of headset... purpose?

Post by Norman H »

It looks like an extra long headset spacer. The stem expander should be below the threaded part of the steerer but with that arrangement it might well not be.
MarcusT
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Re: Tube on top of headset... purpose?

Post by MarcusT »

I agree, it looks like a stem extender, but I must say, that is an ugly bike
I wish it were as easy as riding a bike
rogerzilla
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Re: Tube on top of headset... purpose?

Post by rogerzilla »

Is that a new bike? TSRs (the povvo's version) went threadless years ago.
PT1029
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Re: Tube on top of headset... purpose?

Post by PT1029 »

It isn't like the Stronglight extender, it is just a (very long) headset spacer, so inside the "extra bit" is the fork column. Thus a stem is still clamped inside the fork column.
I too have never liked the Stronglight extender, not a good engineering solution.
Cyril Haearn
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Re: Tube on top of headset... purpose?

Post by Cyril Haearn »

Is there a better solution, to buy or make/have made specially?
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iandusud
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Re: Tube on top of headset... purpose?

Post by iandusud »

This was an option on AMs from the start for taller riders or those wanting a more upright position. It allows the use of a longer steerer tube without the need for a different frame. In fact I think Alex M's personal bike used this arrangement until he came up with the Wishbone stems on the Jubilee.
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Mick F
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Re: Tube on top of headset... purpose?

Post by Mick F »

Seems to me, that it's a sticking plaster approach to combat poor design.
If they wanted a taller quill stem arrangement, the head tube should have been longer.
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531colin
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Re: Tube on top of headset... purpose?

Post by 531colin »

iandusud wrote: 29 Apr 2021, 8:14am This was an option on AMs from the start for taller riders or those wanting a more upright position. It allows the use of a longer steerer tube without the need for a different frame. In fact I think Alex M's personal bike used this arrangement until he came up with the Wishbone stems on the Jubilee.
Thats a one inch threaded steerer?
So there is a huge threaded length, from below the headset top cap to where the locknut fits?
"Standing orders" for threaded headsets include that the quill stem wedge should be below the threaded bit of the steerer; this one can't be, otherwise the extra bit of tube isn't needed.
There is a lot of stress and a lot of leverage on that threaded length of steerer. I don't like it, I think its a poor workaround for a bad frame design.
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NATURAL ANKLING
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Re: Tube on top of headset... purpose?

Post by NATURAL ANKLING »

Hi,
Mick F wrote: 29 Apr 2021, 9:07am Seems to me, that it's a sticking plaster approach to combat poor design.
If they wanted a taller quill stem arrangement, the head tube should have been longer.
Yes.
Someone has already suggested this to give a more upright position without changing the frame.
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leftpoole
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Re: Tube on top of headset... purpose?

Post by leftpoole »

I have been under the impression the extra length can be removed 'cut down' to allow an option to fit an A-head stem.
I recall being told this by another Moulton owner. It is not my assumption.
As a Moulton owner I have a great opinion of these bicycles but admit that Alex Moulton had some silly options on his designs. He did admit once that his designs were always being changed as he found better answers.
Currently the factory is building and has a very long waiting list.
I believe alterations come as and when a better solution is 'discovered'.
Norman H
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Re: Tube on top of headset... purpose?

Post by Norman H »

Is it your bike?

If it is you need to drop the forks and check the length of the threaded portion of the steerer. As I mentioned earlier, and as Colin also suggests, it's critical that the stem is inserted far enough that the expander is below the level of the threads.

Any threads below the level of the stem expander would be perfect stress risers and could lead to steerer failure.
AndyA
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Re: Tube on top of headset... purpose?

Post by AndyA »

Norman H wrote: 28 Apr 2021, 10:45pm It looks like an extra long headset spacer. The stem expander should be below the threaded part of the steerer but with that arrangement it might well not be.
Agreed! If the wedge is in the threaded part of the steerer then you've got a real risk of the steerer breaking there, doubly so if there's a slot. Loads of aftermarket forks are like this, threaded for 150mm or so of the steerer to fit a maximum number of frames. Terrible!
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