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Old 08-28-14, 04:31 PM   #1
RobKelley
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Can you downgrade a Tern handlebar post (Physis --> Telescopic)?

Hi:

Following the theft of my trusty Dahon Mariner, I've recently bought a used Tern Link D8. The original owner did some nice upgrades (better derailleur and seat post), and I'm thinking of my own changes. One thing that's bugging me is that on the D8 the Physis stem collapses to the outside of the folded bike where on the Mariner it tucks in between the two halves.

I know the Physis is a Tern selling point, an awesomely stiff handlebar post, "massively strong, precision machined design that virtually eliminates flex. Four new patented technologies go into the design." That said, it's a little short, it doesn't extend, and it doesn't tuck in for easy carrying. The lower-end Tern Link C7 also tucks in, which got me wondering.

I've started researching the various handlebar posts. ThorUSA.com stocks a lot of Dahon and Tern handleposts, and this site has a lot of just Dahon-brand items . But it seems this may not be an straightforward replacement.

Can I just swap out the handlebar post of a d8 for a c7's? Do I need to replace other parts on the front as well? Will a Dahon telescoping post fit? Again, it looks like there's a lot of options; it's just hard to make sense of what will actually fit.

Thanks for the advice.

Rob

What I have:


What I want:
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File Type: jpg physis3d2.jpg (8.3 KB, 12 views)

Last edited by RobKelley; 08-28-14 at 04:37 PM.
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Old 08-28-14, 04:40 PM   #2
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If its direct fit, I'm interested in a trade. I have adjustable in black.
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Old 08-28-14, 05:51 PM   #3
jur
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I wouldn't do that swap. That particular Dahon stempost has proven notoriously unreliable and hasn't been discontinued for nothing. I can off the top of my head rattle off no less than 6 design deficiencies in that thing.
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Old 08-28-14, 06:28 PM   #4
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Quote:
Originally Posted by jur View Post
I wouldn't do that swap. That particular Dahon stempost has proven notoriously unreliable and hasn't been discontinued for nothing. I can off the top of my head rattle off no less than 6 design deficiencies in that thing.
Um are you referring to Dahon Vector p8 stem? Funny I don't remember thinking about cycling safety when I was a kid..sigh. Off topic I jock that bike of yours Jur. I hate you somewhat and I don't even know ya- kiddin
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Old 08-28-14, 08:11 PM   #5
RobKelley
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Quote:
Originally Posted by jur View Post
I wouldn't do that swap. That particular Dahon stempost has proven notoriously unreliable and hasn't been discontinued for nothing. I can off the top of my head rattle off no less than 6 design deficiencies in that thing.
Jur, thanks for that advice. You have some amazing bikes on your site -- I really like the Raleigh Twenty!

Is there a telescoping handlebar post you would recommend or seen other trustworthy sources recommend (either from the ThorUSA list or from elsewhere)?
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Old 08-28-14, 09:14 PM   #6
jur
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I think the Radius V is an improvement because it uses an external V-clamp technology. Less to go wrong.

There are some who think the original Radius is better ever since Dahon altered the design to mill away less crucial material. However, the basic design is unchanged and all of the deficiencies have been retained.

Maybe ThorUSA could sell you a Radius V. Definitely contact him - he is totally trustworthy and his prices have always been very reasonable. Thor disagrees with me about the Radius issue. Besides that, he will be able to give far better expert advice than me of what can be done. For example, he might be able to confirm if a Dahon post will be able to be installed.

It may be an option to alter the top of your Tern post to accept a Revolve stem. Cut off the top, make a stress relief slot, add a seatpost clamp of the right size, slide in the revolve section and you're done. There will be some things to beware of, I don't know if the diameters of the Tern stempost is suitable for the above mod, and even if the are, the Revolve stem has a system to prevent it from rotating in the bottom section of post, which will be absent in a self-mod. Unless you are mechanically able enough to add such a feature.

Last edited by jur; 08-28-14 at 09:18 PM.
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Old 08-28-14, 09:28 PM   #7
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Just another thing: Folding geometries are usually quite critical and it may not be possible to have the stempost tuck in between. You could form an idea by removing your handlebar assembly from the stempost, loosening the bolts at the bottom enough to allow you to rotate it through 90deg, which will get the post to fold in between. Then you could see the room available.
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Old 08-29-14, 08:07 PM   #8
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Interested to hear how well this works.

Last edited by Hinge; 09-15-14 at 02:57 PM.
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Old 09-02-14, 03:13 PM   #9
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FYI, blopslee responded with this information over here:

Quote:
Originally Posted by Blopslee View Post

As far as I know The standard Dahon handleposts on recent recent models are all the same in terms of the interface with the fork/ headset (might want to confirm with Thor, but would bet they are).

I simply removed the Term handlepost, added a 10mm headset spacer (because the tern has beefier clamp) and a few of those super thin headset shims (that come with lots of headsets or easy to get on ebay/ local shop) to make sure it was not rubbing and it worked super well, held up well over bumps, was reliable, etc. In my experience the inside fold makes the bike much more stable when folded and the magnet faces are better held together without sliding especially if you want to slide the seat up and use it as a handle while walking/ pushing the bike.

As per earlier in this thread - get a Dahon post that folds to the outside if you want it to end up on the inside of the Tern. I'm pretty sure that any telescoping Dahon post will be fine though.

Best of luck!
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