Folding Bikes - 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...

This happened to my Swift Folder yesterday. Crack formed at the top of the compression slot of the stem riser.

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.

Yikes! That's scary! Glad both of you are OK. whew!

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

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 :).

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.

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 ... :D

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

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.

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.

'Died' is indeed melodramatic... I have already turned dozens of schemes for repair over in my mind. :D

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.

:( 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

Sounds like some of that "off-road" riding may have taken its toll on your little gem.

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

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

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 :D

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?

:p

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. :)

Photo at last...

http://i160.photobucket.com/albums/t188/juried/DT%20Mini/brokenhandlepost.jpg

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

The person that designed that should be locked up!

The person that designed that should be locked up!How so? I thought it wasn't bad for the purpose...?:deadhorse:

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

*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.

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?

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. :eek:

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.

The only workaround, I can think of, would be to bond another thick wall steel tube inside the quill tube. I would do that with your replacement one, jur.

The only workaround, I can think of, would be to bond another thick wall steel tube inside the quill tube. I would do that with your replacement one, jur.

I agree it might help to spread out the stress load area by adding support across the weld. If you do decide to add support, I suggest you use the same metal alloy as the quill tube. The last thing you need is to replace a stress issue with an electrolysis issue.

Have you gotten your new riser yet?

Have you gotten your new riser yet?Not yet... I arranged for my boss to carry it accross in his luggage, but then he decided to put it in a box with a bunch of other business stuff which hasn't arrived yet... and I specifically arranged it that way so I could get it sooner! I would have had it long ago if it was posted by Downtube. :mad: :mad: :twitchy:

Not yet... I arranged for my boss to carry it accross in his luggage, but then he decided to put it in a box with a bunch of other business stuff which hasn't arrived yet... and I specifically arranged it that way so I could get it sooner! I would have had it long ago if it was posted by Downtube. :mad: :mad: :twitchy:

Rats, rats, rats ! ! !

Well, maybe you would get it sooner...

I used to go nuts trying to ship internationally. There is all this paperwork, and 2 sets of customs. Either 1 set gets returned with a nasty note that you left out the comma on page 6 of 12, so you have to resubmit it (which means a NEW set for the other customs and another chance for a bounce back) OR the shipment sort of goes through, but the customer gets a nasty note that something wasn't quite right, so the package must be picked up and personally brought in. The customer only has to drive 300 miles, get chewed out for whatever the problem was supposed to be, fill in more paperwork, and usually pay an additional customs fee that is not in fact a legal fee.

I hope you get your part soon.

Rats, rats rats! :mad: :mad: :mad:

It now appears the parcel which my boss arranged to get sent, which also contains my replacement handlepost, is missing! Tracking number doesn't work and everybody claims innocence. In in the meantime my Mini gathers dust...

Gunna have to approach Yan for yet another one. Damn!

Damned bad luck that. It must have transited through Heathrow Terminal 5. It's a black hole.

Gunna have to approach Yan for yet another one. Damn!

Maybe this is a good thing, afterall, wouldn't you rather have the new 2009 handlepost that folds to the inside of the frame? :innocent:

Maybe this is a good thing, afterall, wouldn't you rather have the new 2009 handlepost that folds to the inside of the frame? :innocent:Yep, I asked Yan if he has the new ones spare. But the current one can also very easily be arranged to fold to the inside. Just loosen the quill bolt and rotate 90 deg.

Well Yan continues to be generosity itself. He didn't have to do it, but he waived any money and is sending me another handlepost. What a guy. :)

I looked over the crack in mine again, and found a second crack, also in the weld, but on the left side only. I think it must have happened when I crashed on the tour I did on the Mini, after grinding to a halt while crossing some deep gravel and not unclipping fast enough. The bike & I fell to the left and that's when it might have started, and propagating over the next few weeks of normal use.

I will now go over the frame with a magnifier as well.

Well Yan continues to be generosity itself. He didn't have to do it, but he waived any money and is sending me another handlepost. What a guy. :)


That's very impressive :thumb:. Downtube is still small enough to be run with heart.