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  1. #1
    jur
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    My Downtube Mini died...

    The folding handlepost riser broke off below the hinge. Photos later. Off to bed now. Luckily I wasn't doing breakneck speed.

    I hope Yan has spares...

  2. #2
    Senior Member law4jba's Avatar
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    This happened to my Swift Folder yesterday. Crack formed at the top of the compression slot of the stem riser.

  3. #3
    Bicycling Gnome
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    Sorry to hear the bad news from both of you gents. What a disappointment for you.

    Damned good job neither of you pitched head first onto the road. It could have been a disaster rather than a pain in the arse.

    I suppose that the long handlepost design gives rise to heavy loads at the base doesn't it. That combined with the use of fatigue prone aluminium alloys is a recipe for disaster. This is one reason I like the steel handlepost on the Merc. It really looks bomb proof as far as that kind of failure is concerned. Little Pixel just sent me a ton of spare parts left over from his Mercton Fixie project and that was just about the only part that I declined because it is so strongly made..... I'm just wondering if I should have asked for it to be included.

    As an aside - Little Pixel is a top bloke in my opinion. He sent me the stuff beautifully packaged for the cost of the postage and a meager donation to his beer fund.

  4. #4
    Eschew Obfuscation SesameCrunch's Avatar
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    Yikes! That's scary! Glad both of you are OK. whew!

    Geez, what a bad luck day yesterday was. Your handlebars, my rear axle...

  5. #5
    Eschew Obfuscation SesameCrunch's Avatar
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    Quote Originally Posted by EvilV View Post
    As an aside - Little Pixel is a top bloke in my opinion. He sent me the stuff beautifully packaged for the cost of the postage and a meager donation to his beer fund.
    I'll second that! He sent me some parts also, all the way across the pond. He's some man for one man - as the Irish would say .

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    Quote Originally Posted by EvilV View Post
    I suppose that the long handlepost design gives rise to heavy loads at the base doesn't it. That combined with the use of fatigue prone aluminium alloys is a recipe for disaster.
    While the main frame of the Xootr Swift is aluminum the fork and stem riser are both steel.

  7. #7
    Part-time epistemologist invisiblehand's Avatar
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    If it is no longer under warranty, I believe Yan has them for sale on his website.

    "Died" is an overstatement ... don't you agree Jur? All the king's horses and all the king's men can still put the Mini back together again ...

    Glad that your teeth are still in their original places Jur.

  8. #8
    Bicycling Gnome
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    Quote Originally Posted by JonathanG View Post
    While the main frame of the Xootr Swift is aluminum the fork and stem riser are both steel.
    Oh - sorry for the wrong assumption. That must have taken some force to break then unless it's very thin gauge tubing. I wonder if it was a welding / brazing fault.

  9. #9
    Senior Member law4jba's Avatar
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    Quote Originally Posted by EvilV View Post
    Oh - sorry for the wrong assumption. That must have taken some force to break then unless it's very thin gauge tubing. I wonder if it was a welding / brazing fault.
    Tubing cracked around the circumference of the tube at the middle of the round hole at the top of the compression cut out. Hopefully that makes sense. I'll try to upload pictures of the crack when I take install the replacement.

  10. #10
    jur
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    'Died' is indeed melodramatic... I have already turned dozens of schemes for repair over in my mind.

    The bottom section of the handlepost is a quill style; it was still held together by the quill tightening bolt. It went from slightly loose to uncontrollable over about a mile. I first though the bolt was simply loose. I had forgotten to pack a minitool so I couldn't stop to tighten it, which in hindsight was a blessing in disguise, as tightening it may have hidden the break. In fact I wonder if I had actually ridden with the break for some time. I'll do a careful inspection tonight when I get home.

  11. #11
    Gak! Wud's dat smell??? Archer-ca's Avatar
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    Wow! Glad to hear both you gentlemen are ok. A good lesson to have quick inspect of your bits and bobs before a ride...just in case...

    Take care,

    Norman

  12. #12
    Senior Member Foldable Two's Avatar
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    Sounds like some of that "off-road" riding may have taken its toll on your little gem.

  13. #13
    Senior Member Speedo's Avatar
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    Quote Originally Posted by jur View Post
    The folding handlepost riser broke off below the hinge.
    My condolences, but it sounds like it's only wounded.

    We have faith in Dr. Jur!

    Speedo

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    Sounds like Jur's money went DOWN THE TUBE.....get it? Downtube?...kidding

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    Quote Originally Posted by jur View Post
    The folding handlepost riser broke off below the hinge. Photos later. Off to bed now. Luckily I wasn't doing breakneck speed.

    I hope Yan has spares...
    Sorry for the loss. Got photos? I'm interested in one of these DT bikes and would like to see where I should look before I ride

  16. #16
    SWS: Small Wheel Syndrome kb5ql's Avatar
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    That's what you get for riding it. You know it supposed to stay garaged, right?

    And what's this nonsense with you actually touring with it?


  17. #17
    jur
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    No photos yet, I'm a lazy bugger... Hopefully I can motivate myself tonight.

    I'm happy to report that Downtube is treating this as a guarantee replacement, which is much more than I hoped for after the hard work I doled out to the Mini - it was not really designed/ expected to be able to do that sort of work. So kudos to Downtube for yet again going beyond what is required!

    I will certainly from now on use lower gears when standing on my various bikes' pedals on the hills instead of pulling on the handlebars in too high a gear. My knees and elbows will thank me too.

    They are sending the replacement handlepost to a firm in Philadelphia where my boss happens to be.

  18. #18
    jur
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    Photo at last...



    I now have the perfect excuse to see if I can modify the forward leaning angle.

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    The person that designed that should be locked up!

  20. #20
    jur
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    Quote Originally Posted by MilesH View Post
    The person that designed that should be locked up!
    How so? I thought it wasn't bad for the purpose...?

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    They've created a stress raiser at the worst possible point.........

  22. #22
    jur
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    *goes off, checks stress riser on wikipedia...*

    I see what you mean. The welding fillet macroscopically spreads the load transition but microscopically there would be local stress risers. I also wonder if these have been heat treated after welding.

    Hmmm... I think I may polish the new one and get it shot-peened before re-anodizing it.


    I inspected the break surface and it is mashed flat. Not sure if this was due to the last mile's movement, or whether this is a longer term break with the break surfaces operating under compression from the quill bolt.

  23. #23
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    Quote Originally Posted by jur View Post
    I see what you mean. The welding fillet macroscopically spreads the load transition but microscopically there would be local stress risers. I also wonder if these have been heat treated after welding.
    The primary error is the reduction in diameter and cross-sectional area at the point of maximum stress

    Is this design common to all the Downtube bikes, jur?

  24. #24
    jur
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    Quote Originally Posted by MilesH View Post
    The primary error is the reduction in diameter and cross-sectional area at the point of maximum stress

    Is this design common to all the Downtube bikes, jur?
    Yes, AFAIK, haven't seen any others but on this part they are the same or similar.

    The way it was constructed, is the hinge plate has this socket at the bottom into which the quill tube is inserted and welded. It appears to my untrained mind a solid design.

    While this part is similar, what is different on the other bikes is the work-load my Mini gets subjected to.

  25. #25
    Bicycling Gnome
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    Quote Originally Posted by MilesH View Post
    They've created a stress raiser at the worst possible point.........
    Would it have been better to continue the lower diameter tube right to the base of the hinge? Then there wouldn't have been a change in shape. How would that have been different to what was actually done from a stress concentration point of view? I only know what I read on Wikipedia about this.

    This stuff seems counter intuitive to me, but it's very interesting. In my simple minded way, I'd have expected that beefing up the part where it enters the hinge plate would be a good idea. It seems that on the contrary, it made things worse because of the steep transition in diameter from the support at the hinge plate to the quill tube. The quill tube obviously has to be of a smaller diameter.

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