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Old 05-06-08, 06:43 AM   #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...
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Old 05-06-08, 06:55 AM   #2
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This happened to my Swift Folder yesterday. Crack formed at the top of the compression slot of the stem riser.
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Old 05-06-08, 07:09 AM   #3
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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.
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Old 05-06-08, 07:14 AM   #4
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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...
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Old 05-06-08, 07:16 AM   #5
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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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Old 05-06-08, 07:58 AM   #6
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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.
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Old 05-06-08, 10:49 AM   #7
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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.
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Old 05-06-08, 11:32 AM   #8
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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.
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Old 05-06-08, 01:05 PM   #9
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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.
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Old 05-06-08, 06:00 PM   #10
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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.
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Old 05-07-08, 07:51 PM   #11
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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
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Old 05-07-08, 08:33 PM   #12
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Sounds like some of that "off-road" riding may have taken its toll on your little gem.
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Old 05-07-08, 08:56 PM   #13
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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!

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Old 05-07-08, 09:01 PM   #14
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Sounds like Jur's money went DOWN THE TUBE.....get it? Downtube?...kidding
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Old 05-08-08, 07:32 AM   #15
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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
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Old 05-08-08, 10:55 AM   #16
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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?

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Old 05-08-08, 05:39 PM   #17
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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.
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Old 05-09-08, 05:20 AM   #18
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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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Old 05-09-08, 05:58 AM   #19
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The person that designed that should be locked up!
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Old 05-09-08, 06:32 AM   #20
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The person that designed that should be locked up!
How so? I thought it wasn't bad for the purpose...?
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Old 05-09-08, 07:15 AM   #21
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They've created a stress raiser at the worst possible point.........
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Old 05-09-08, 05:39 PM   #22
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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.
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Old 05-09-08, 07:55 PM   #23
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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?
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Old 05-10-08, 01:14 AM   #24
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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.
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Old 05-10-08, 01:55 AM   #25
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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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