Paluc52

Modifying the cockpits on an aluminum-framed tandem, I'd like to use a Specialized CG-R carbon seatpost for the captain. Should I be concerned about the lateral stress caused by the stoker's stem? Obviously, I should be very careful not to overtighten the stem.

Sprout97 

And rightly so. The Specialized is a 27.1mm shaft diameter. That's fine for supporting you on your half bike. Not as a fulcrum for the stoker bars. I'm running an oversized 31mm Wound Up Composite seat post. I haven't had an issue with it for the 8-9 yrs that I've been using it. But again, it's a bigger seat post. And my wife's weight won't stress anything. Except maybe me on a long climb.

Chris_W

Why would you need a CG-R or any carbon post for a tandem captain seatpost? The captain's saddle is so far from either wheel that shocks are mostly absorbed by the frame before reaching the seatpost, I really don't think that the CG-R is going to be very effective or necessary. If you want slightly more comfort, try 10 psi less in the tires first.

Tandem2

I was wondering the same thing, we have been using an alloy post on our Fuji.
While anxiously waiting for the completion of our Supremo frame, I have been collecting bits for the build, one of those bits is a FSA SLK 31.6 captains post.
I was/am leary of this choice, but see so many new Tandems specced this way.

merlinextraligh

I agree you don't need a CF seat post, but if you're going for an uber light build it helps a bit. Also if everything else is carbon,particularly the stoker's seatpost, then it will help with the matching aesthetics.

We've had a Co-Motion Robusta with a 29.8 Alpha Q CF seatpost, and a Calfee Dragonfly, with a 27.2 ENVE seatpost, and have had zero issues, with the captain's seat post. The Robusta has something like 30,000 miles on that configuration, including racing, and sprinting an climbing out of the saddle, and we're not a small team.

Reputable tandem makers wouldn't spec bikes with CF seatposts if it were a significant issue.

zonatandem

Our all-carbon custom Zona tandem was built in 2003 including c/f pilot and stoker bars, c/f seatpost for stoker and c/f stoker stem + a custom c/f rear rack. Weight: 26.5 lbs.
45,000+ miles on that tandem, no issues so far. Attached pics of when new, and shot taken last year in Logan, UT.
In our opinion/experience there is no need for pilot suspension; heck, stoker Kay has only test ridden various suspension seatposts and never has used one on any of our 5 tandems snce 1975.
Pedal onTWOgether!
Rudy and Kay/zonatandem

TandemGeek

I've used 27.2 aluminum, titanium and Easton carbon seat posts without any issues on our tandems. The Easton EC90 was a fairly robust CF seat post but, like all captain's seat posts, success or failure is not a level playing field. I don't have a lot of exposed seat post mast on our road tandems and given our riding positions Debbie's stoker stem clamps on at the bottom of the seat post just above the seat tube clamp, see photo below. The same was true on our other road tandems.



Debbie is also a very slight stoker of 62" in the 110-120 lbs range who doesn't input much in the way of loads on her handlebars and I'm also a very lightweight rider. So, our success or failure would not be as useful as a benchmark vs. Merlin and his stoker who are both larger riders, or with someone whose stoker has to have the stem attached at the top of the seat post, just under the saddle clamp. Just something to keep in mind when getting feedback on what works and what doesn't.

Now, all that said, I decided to use Thomson's aluminum Masterpiece seat posts on our Calfee build back in 2008 because after comparing them with all of the other alternatives to include the composite posts that were available at the time, the Thomson Masterpiece were about as light as the composite alternatives and less expensive. Moreover, the Thomson seat posts are notoriously robust. So, as you evaluate your alternatives be sure to look at the cost benefit of the various different materials used for some of those component decisions, you might be surprised by what you find.

jnbrown

I also use a Thomson but the Elite model which I think is slightly heavier and thicker wall than the Masterpiece.
I felt better using it over a carbon post but not sure it matters that much. There have been reports of Thomson posts breaking on singles so there is no guarantee when using lightweight components. I think carbon is not a problem as long as there are no sharp edges digging into it from the stoker stem and stem is properly torqued.