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Old 11-06-13, 09:01 PM   #1
5b00
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Unwanted rotation in Dahon adjustable handlepost

Does anyone else have excessive play in Dahon adjustable handleposts? I'm aware that this was brought up in 2008, but I'd like to see whether current designs have solved the problem or whether I should give up and get a fixed handlepost.

Dahon - A potential SAFETY ISSUE

My handlepost rotates around the steering axis with just a light touch, even with the quick-release tightened as tight as I can get it (ludicrously so). I measured the play to be about 13 degrees, which means that it moves by more than an inch at the end of the handlebars. The play has gotten so bad that the steering is extremely imprecise: in leaning turns there's always a scary moment where the handlebar and the wheels decide that they want to go in opposite directions. I've almost bitten it trying to balance when nearly-stopped.

I'm pretty sure that the play results from wear on the inner and outer pieces of the handlepost, especially wear on the anti-rotation dimple. Here are some pictures:

This shows the pattern of wear around the dimple. Sorry for the weird shadows.


This shows some galling on the inner part, which may not be a direct cause of the play but gives some perspective on how tight the clamp has been. The wear also suggests that the clamping force is unevenly distributed. It also creaks like crazy unless I ride no hands. I am closely monitoring this area for cracks. The parts in the shadow are worn from rubbing against the dimple.


You can see that the inner part is damaged by resting on the bolts holding the clamping mechanism in place on the outer part. For a while, this was a good thing because it held my handlepost in a consistent position. Now the two indentations are wallowed out and also contributing to the creakiness.


Looking down into the outer part. The two circles in the middle are the bolts that bump against the inner part.


I am using bullhorn handlebars and do standing sprints away from traffic lights, so it's conceivable that I'm putting more force than was intended to be handled by the design. I have less than 1500 miles on my handlepost in the current configuration, and only about 500 miles on it before with a flat handlebar. I did saw about an inch off both ends of the handlepost to make it shorter (bottom of the inner, top of the outer), but I'm confident that this particular modification is not a direct cause of the wear.

Any other reports? Advice?
Attached Images
File Type: jpg inner handlepost 1.jpg (35.2 KB, 30 views)
File Type: jpg inner handlepost 2.jpg (38.8 KB, 23 views)
File Type: jpg outer handlepost 1.jpg (30.8 KB, 32 views)
File Type: jpg outer handlepost 2.jpg (34.4 KB, 22 views)
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Old 11-06-13, 10:53 PM   #2
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I am using bullhorn handlebars and do standing sprints away from traffic lights, so it's conceivable that I'm putting more force than was intended to be handled by the design. I have less than 1500 miles on my handlepost in the current configuration, and only about 500 miles on it before with a flat handlebar. I did saw about an inch off both ends of the handlepost to make it shorter (bottom of the inner, top of the outer), but I'm confident that this particular modification is not a direct cause of the wear.


well..... ??
That seems to be a different post than I am used to... does the picture show some kind of shim ? or is that the part you cut off ? The clamp is at a strategic position and if you cut the top off, it might not work as intended....

The above copied sentence from you..
Standing sprints with a bullhorn bar... did that Bullhorn bar came standard ? As far as I know all Bullhorn bar equipped bikes have T - onepiece tops and are not adjustable in height ... well a little with the syntace double clamps... I am sure that is the reason for your handlebar turning ...

The slot and the knob are there that the handlebar if it is loosened not turn all over the place, and to guide it somewhat in a general correct position when you close it again, after it has been folded, but not to keep the handlebar from rotating when the quick release is closed properly.

You should invest in a Jetstream one piece stem. that will get you down in front, and will eliminate the rotating all together. And I do have them back in stock as well.


http://www.thorusa.com/images/dahon/...es/jetstem.jpg

Best Thor
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Old 11-07-13, 07:11 AM   #3
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This is my setup. The bullhorn handlebars have a 25.4 mm stem clamp section and I had to relocate the grip shifter to a computer mount accessory bar.


The "shim" that you see is actually the top edge of the outer piece. It's bright at the top because that's where I sawed through. The clamp is still sort of in its original position with the screw attaching it to the dimple, but it's now closer to the handlebar by about an inch. I've read many of the posts about moving the clamp, and I don't understand the vague claims about there being an effect on the torsional rigidity. Are you saying that it's because I've removed some of the clamping surface above the clamp and that if it were still there, the post wouldn't be worn and twisting this much?

I'm aware that I fall outside of Dahon's intended use case and that my modifications really muddy the issue. But I still believe that the adjustable handlepost design is far from over-engineered and foolproof (maybe that makes me a fool). I just want to understand whether this is a typical failure mode and whether the solution is just to buy another post once the dimple is worn down.

Thanks for the comments, Thor. I'll probably be buying the Jetstream handlepost from you soon!
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Old 11-07-13, 12:08 PM   #4
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I am not a engineer... :-) and even if .. it would be difficult to say if the extra material which you cut off above the clamp, will have any effect.
The knob is there for general guidance when you have to loosen the stem in order to fold it. Its not designed to keep the bar from rotating ... it will do that to an extent obviously,preventing the bar to fully swing around.

Whats definitely not designed for is to have a bullhorn bar on a height adjustable stem ... that together with sprinting standing up mashing the gears is definitely the reason for failure...

I am positive that a Jetstream T one piece post will be the answer...
best Thor
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Old 11-07-13, 05:16 PM   #5
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I'm curious what's going on with the brake levers. Why would you move them to two different places?
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Old 11-07-13, 07:31 PM   #6
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Originally Posted by dynaryder View Post
I'm curious what's going on with the brake levers. Why would you move them to two different places?
The front/left TT brake lever is for harder braking in the forward position. The rear/right interrupter lever is for lighter braking at slow speeds, in a more upright position. I took out the right TT lever because I never use it.
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Old 11-07-13, 08:15 PM   #7
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Originally Posted by 5b00 View Post
The front/left TT brake lever is for harder braking in the forward position. The rear/right interrupter lever is for lighter braking at slow speeds, in a more upright position. I took out the right TT lever because I never use it.
LOL! I can understand the rationale. On my ghetto track bikes (hipster fixies ) with bullhorns, an asymmetrical placement of the brake levers (only got two in the parts bin so that's what I have to work with) would still allow some form of emergency braking regardless of hand position. Looks unconventional but it works.
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Old 11-08-13, 08:17 PM   #8
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I like this setup most. From turning drops upside down and cutting back. Even better with dual drive and brifters like on my mezzo. On this brommie it folds completly flush using the dahon stem extender.
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