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Quill height vs steer tube length

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Quill height vs steer tube length

Old 07-13-22, 05:35 PM
  #1  
dmwill
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Quill height vs steer tube length


Adding Jones H bar to Burley Samba
Any unforeseen consequences from having a quill longer than the steer tube? The tube is 18cm and the quill is 22cm. The quill is inserted to the minimum distance mark, so that makes me think it's ok but it looks kinda funny and I'd hate to split the steer tube from the extra leverage or something.
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Old 07-14-22, 07:28 AM
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That is a lot of extra leverage given the height of the quill. I think I'd probably have it a little lower than the minimum distance mark just to provide a bit of margin. But I don't see any reason that the length of quill compared to length of steerer would particularly matter. Even if the headtube and steerer were a good deal longer, that wouldn't change the extra leverage from the long height of the quill.
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Old 07-14-22, 12:36 PM
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I wouldn't worry about it. Assuming the headset is properly adjusted and functioning well. And there's enough overlap of the quill within the steerer tube. (If in doubt, drop it below the max height line a few cm for peace of mind.)

Think of the difference in leverages on the steerer tube:

1) Your upper body on the handlebars. Sure, you're exerting more leverage, but it's just you pushing with your arms. Not even your full body weight. Unless you're planning on doing handstands on the handlebars. And during a hard stop, you are exerting more force to the bars, but still not more than your body weight.

2) The fork legs. The fork is supporting both riders riding through potholes, bumps, rocks, roots, you name it. That's a ton of instantaneous force acting on the fork blades, which are even longer than your quill/stem/handlebar lever arm. And then think of panic braking. That force is acting perpendicular to the head tube (mostly) and utilizing the entire fork as a lever arm. And it's having to withstand the braking forces exerted by two riders. Now THAT is some MAJOR leverage on your fork's steerer tube. So if this is indeed a tandem fork, then it's been designed with these incredible leverage forces in mind.

Now the only concern I might have would be the forces exerted on the head tube. During a panic braking situation, you would be loading the head tube considerably, and from both sides. During hard braking, your front wheel axle is pushing back hard on the fork legs. And you're pushing forward on the handlebars - and even moreso with a longer quill. So you have a sum of these two forces acting on the head tube pulling it forward off the top tube, and backward against the downtube. THIS could possibly be problematic. So if you DID have a failure, I'd expect it to be along these lines.

But if this is a tandem frame worth more than junk,* it should have been designed to withstand these forces.

*After a closer look at your picture, I see it's a Burley frame. This is a respected tandem maker, so you should be just fine.

Last edited by LV2TNDM; 07-14-22 at 04:35 PM.
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Old 07-15-22, 06:25 AM
  #4  
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Thank you for that thoughtful analysis! I lowered it down a cm or so (as far as it would go) and will give that a try without worrying too much.
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Old 07-18-22, 07:49 PM
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Why such a long quill? Is the front of the bike way too small for you? Personally, I would not feel comfortable with a quill that long inserted anywhere close to the minimum distance and would worry about too much stress on the steer tube. It doesn't matter whether it's a Burley or a piece of junk - the steerer tube was not designed for a quill that long.
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Old 07-19-22, 07:08 AM
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We've been bikepacking on Trek Verves. They are more upright than a straight bar MTB but certainly not full leisure cruiser. We can and have ridden those things all day carrying a fair bit of weight so wanted to somewhat mimic the contact points from the Verve on the Burley. The Burley came to me with a high quill, narrow drop bars, and bar end shifters (I think it came from the factory with straight bars and a lower quill but I didn't get those with the bike). The height of the bars was fine, but the narrowness made everything seem wobbly, especially letting go to shift. So we settled on a Jones Loop H-Bar as something that would give a wider grip for leverage, multiple hand positions, MTB style shifting and braking I can do without letting go, and a way to put my elbows down if I need to fight a headwind for a while. A Moloko or Crazy Bar would work similarly, but we like the loop.
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Old 07-22-22, 06:00 PM
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What could possibly go wrong with that setup?

Personally, I’d sell the bike and buy one that fits
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Old 07-23-22, 04:24 AM
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Personally, I wouldn’t feel comfortable with that setup. This based on little more than concern of any outcome from a failure.

If your goal is to raise your handle bars a large amount, you might consider BMX, or ape hanger style bars with a more conventional stem.
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