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Single bolt Bontrager carbon seat post is a PITA!

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Single bolt Bontrager carbon seat post is a PITA!

Old 07-07-19, 07:45 PM
  #1  
Lotus907efi
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Single bolt Bontrager carbon seat post is a PITA!

The custom Taylor frame I recently purchased came with this fancy carbon seat post made by Bontrager. It is a weird single bolt design where there is a horizontal stud that has left hand threads on one end and right hand threads on the other end and there are these tapered pieces that fit into a circular hole in the top of the seat post.

The seat post was shipped to me with the frame and it had all of the mechanical bits in a separate ziplock bag so not parts would be lost. So today I attempted to install a seat onto the top of this post and I found out this fancy single bolt design is a royal pain in the ass.

Anyone ever have any experience with one of these things?

The assembled seat post looks like this:



closeup of Bontrager single bolt seat post
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Old 07-07-19, 07:56 PM
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My advice in the short term is to put carbon fiber grip paste on the cones to try to stop it from slipping-- because it's gonna try to slip. My longer term advice is to buy a different seatpost. I dealt with a very similar Bontrager post awhile back, and it was relegated to the parts bin rather quickly. I recommend the FSA SL-K ITC post-- it uses a three bolt design, so you can adjust fore-to-aft and tilt independently. Also fairly light, and pretty cheap-- I've seen 'em on eBay as low as $30.
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Old 07-07-19, 07:57 PM
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Detail shots of Bont seat post bits

Here are some detail shots of the bare top of the seat post and a closeup of the mechanical clamp bits



Top of the seat post with the mechanical clamp bits removed


Closeup shot of the clamp pieces of the Bont seat post
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Old 07-07-19, 08:01 PM
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Originally Posted by DrIsotope View Post
My advice in the short term is to put carbon fiber grip paste on the cones to try to stop it from slipping-- because it's gonna try to slip.
Actually one of the problems I have is that I am not able to get the cones to move so I can set the front to back angle of the seat. Even with the clamp stud fairly loose so that the outer two threaded clamp plates are flopping around, I cannot get the cones to easily rotate so I can have the angular orientation of the two cones aligned with each other and it is nearly impossible to easily set the rake of the seat once it's even lightly installed into this fancy clamp assembly.
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Old 07-07-19, 08:12 PM
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Sounds about right. Small adjustments are nearly impossible-- you have to "adjust" the saddle around by whacking it with the palm of your hand. But no matter how tight you get the bolt, the cones will try to slip.
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Old 07-07-19, 08:50 PM
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Also even if I crank on the adjustment screw, the saddle still flops around in the clamp. When it is all tight, the clamps pieces and the cones are not moving but it does not actually hold the seat firmly.

Basically this seat post design is a real piece of crap.
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Old 07-07-19, 10:04 PM
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There's an easy solution. Get a different seatpost, preferably one that uses two bolts (Thompson is one). I hope this bike has a standard diameter round seatpost and not one of those cursed streamlined ones.

Life's too short and seat position is way too important to use a less than good seatpost. (I've had a local framebuilder make me two posts with the large setback those bikes were designed around and Thompson hardware. Also picked up a couple of SR MTE-100s (model name from memory; don't quote me); the adjustable super-long setback MTB posts and a new and gorgeous Nitto lugged steel 2-bolt post.)

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Old 07-08-19, 08:41 PM
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Yeah, I've dealt with this junk too. Epic fail from Trek/Bontrager. Bloke I used to work with called em Butt-rager.
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Old 07-08-19, 09:06 PM
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Piling On...

And so ... , you just buy another seat post... does it have to be Carbon?

just match the diameter,, what is it? 27.2 mm?

2 bolt micro adjust, even in aluminum, has many fine offerings..


I, OTOH, in the single bolt category, find the one in a saddle clip format , the Pentaclip,
from Brompton..

Of mostly aluminum , with a multi plate clutch like friction clamping system
holds the angle securely, with my 230# on the saddle ..

Seeing sold in the aftermarket, the 1 steel part, the bolt, is duplicated in Titanium ..


The single bolt , from underneath, Campagnolo seat post also seems to work fine,
for these past 30 years, too ..



I don't think the designer was Mr. K Bontrager , just Trek badges a lot of their stuff with his name,
for some reason.



...

Last edited by fietsbob; 07-09-19 at 08:38 AM.
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Old 07-09-19, 07:07 AM
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I had my first Thomson maybe 20 years ago. For the life of me I can't understand how that clamping design hasn't become ubiquitous. It's superior to everything else I've seen. There are more affordable offerings with that seat clamp design.

Some caveats. The cheap eBay seatposts have a very similar looking design. The rail clamp part is thin aluminum. I broke this clamp on it's first ride. So you need to be careful about going cheap. I think the Origin8 I replaced it with will last longer than the bike.

I have an older titanium Campy Chorus post on my good bike. It took a few months and much pain to finally get it adjusted right. Normally I wouldn't try so hard but it's a damn cool post. It's got the old school single bolt design. I'm pretty sure that if I ever need to replace my seat, I'll replace the seatpost with it.
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Old 07-09-19, 10:40 AM
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Originally Posted by rosefarts View Post
I had my first Thomson maybe 20 years ago. For the life of me I can't understand how that clamping design hasn't become ubiquitous. It's superior to everything else I've seen. There are more affordable offerings with that seat clamp design.
Because weight weenies can just feel the extra 10 grams of that second bolt dragging, dragging, dragging on them with every pedal stroke.

Why would Bontrager want a well-engineered, reliable solution that probably costs more to make, when they can save a few grams and charge more to boot.
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Old 07-09-19, 10:43 AM
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Originally Posted by Lotus907efi View Post
Also even if I crank on the adjustment screw, the saddle still flops around in the clamp. When it is all tight, the clamps pieces and the cones are not moving but it does not actually hold the seat firmly.

Basically this seat post design is a real piece of crap.
Sounds like the rails are meant for oval carbon railed saddles.

I just went through this with a Black Inc seatpost of the same design. Glad it's a buddy's and not mine.
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