Tandem Cycling - 200 gram savings $7

Found a 140mm Easton stem on Ebay for $7 to replace the adjustable stoker stem.Will go from 360 grams to 160grams.

I think it should be just long enough. The current stem is actually extended to 160mm. However, its 17 degree rise. 140 mm with 6 degree rise will allow the stem to be more than an inch up the seatpost. (moving the bars back due to seatpost angle) and the difference in rise is worth about 1/2cm itself base on the Habenero chart.



And if it doesn't fit,its only $7.

Nice move! That's the way to shave grams with pennys, ya gotta love. I'm trying to do the same thing with our adjustable stoker stem but haven't found the correct fixed stem yet.

That Habenero chart is great by the way, thanks.


KRhea

I just got my stem (probably from the same seller..abaxo?) in the mail yesterday. I wonder where in the world he got those so dirt cheap. He also had Cane Creek headsets for $15-20, depending on model.

glad to hear you actually got one. It was so cheap, I was thinking there had to be some catch.

If you can get away with a standard threadless stem for use as a stoker stem that's a good deal. Of course, it's also a double-edge sword as it means your stoker's nose is usually in the middle of your back side.

As for stems going at blow-out prices, one of the other list members recently mentioned someone was blowing out Ritchey stems for about $20. It does make one wonder.

I would like to replace the adjustable that came on our Santana with a fixed. We have it all the way down and collapsed in so adjusments not needed. Problem is the Santana 29.6 seatpost.
Haven't been able to find anything. Hell I'll pay $200 to save 200 grams.

^ I think you just need to find the right sized shim.

The 29.6 is only .040" bigger than the 1 1/8" stem..you could easily hone that much from the stem ID without worrying, IMO.

Got the stem and put it on. The 140mm stem puts the stoker's bar within a couple of mm's of where it was with the adjustable stem.

Actually measuring it out, the 140mm stem ended up giving the same extension as the Co-Motion adjustable stem extended to 175mm.

The Co-Motion stem appears to have about 30 degrees of rise. ( I was wrong when I thought it was 17, which is obvious thinking about it, because it still gives a lot of rise mounted on a seatpost angled at 73 degrees, and +17 would give it zero rise.)

The 140mm +6 degree stem ends up mounting approximately 4 inches farther up the seatpost to get the handlebars at the same height. And this 4 inches up on a seatpost sloping backwards ends up putting the hadlebars in the same place with a 35 mm shorter stem. If you needed even more extension, you could flip the stem, make it -6, move the stem up the seatpost, and have the same height for the bars but slighty further back. (again because the seatpost slopes backward.)

So the moral of the story is that you may be able to get your correct fit with a regular fixed stem, even if you're currently running your adjustable seatpost well beyond a standard stem length by using a stem with little rise. (of course this assumes that the stoker's handlebars are set up below the captain's seat.) A little trigonometry (or some trial and error) can calculate the fit.

Merlin, thanks for the great tip on the stem deal. I got mine yesterday and will be including it as my build continues. I think it's gonna work fine as you said, by raising it up the post and "flippin" it, but again, the big deal is the amazingly ultra-cheap yet huge weight savings it provides. I'm really hopeful our fit guy can make it work. If not, oh well, $7 gone.

My stats were: 325gr for the adjustable stem versus 184gr for the fixed. A few savings like this here and there on the bike and it all adds up. If I can shave another pound without risk or ridciulous expense I'm a happy man. Another 312grams and another pound drops off the bike. Not sure where I'll find the 312gr but I'm lookin'. Perhaps a lighter tube, maybe I'll use 2 Thomson Masterpiece posts instead of one or a lighter stoker bar, lighter skewers etc. I also have a couple sets of Nokon cables I might toss on for bit of weight savings.

I'm not a weight weenie tandem guy by any stretch but boy it's fun putting a bike on a "Jenny Craig" program. I like it when my bike "loses" weight, even if it's purely "fantasy" I still feel faster gosh darn it!


Yo Merlin, find me a couple more elcheapo weight saving deals my friend.


KRhea

Found some extra long stems, some upto 165mm at hbtrails.com.

http://www.hbtrials.com/stem_en.html

Found a 140mm Easton stem on Ebay for $7 to replace the adjustable stoker stem.Will go from 360 grams to 160grams.

I think it should be just long enough. The current stem is actually extended to 160mm. However, its 17 degree rise. 140 mm with 6 degree rise will allow the stem to be more than an inch up the seatpost. (moving the bars back due to seatpost angle) and the difference in rise is worth about 1/2cm itself base on the Habenero chart.



And if it doesn't fit,its only $7.

Just curious, I'm assuming you got a 1 1/8 (28.6mm) threadless stem, and fitted it to a 27.2 seatpost, or some seatpost size that required a shim.

Guess the bottom line is, were these Eastons 1 1/4".

PK

Here is a 130 gram saving (over a Co-Motion stem) for $85:

http://www.webcyclery.com/product.php?productid=18468&cat=478&page=1

It's a 185mm x 35 degrees fixed stem for a 31.8mm handlebar. I think the Co-Motion stem is also 35 degrees. We have ours adjusted to 185mm. I can't get the height needed with the options discussed above.

The weight is similar to an adjustable carbon stem.

Just curious, I'm assuming you got a 1 1/8 (28.6mm) threadless stem, and fitted it to a 27.2 seatpost, or some seatpost size that required a shim.

Guess the bottom line is, were these Eastons 1 1/4".

PK

I believe the seatposts on Co-Motions are 28.6mm

In fact, Co-Mo uses 29.8 seatposts on their tandems. Probably because they "leveraged off of" (as opposed to copied :-) Santana standard practice at one point in their early history. It would be nice if the tandem world would standardize on 28.6, but that's not likely to happen anytime soon... If ever.

The robusta appears to be 28.6 From the web page:

Robusta Frame Specifications
Frame Size 21/18 22/19 23/20 23/18
Head Angle 73˚ 73˚ 73˚ 73˚
Seat Angle, Captain 73˚ 73˚ 73˚ 73˚
Seat Angle, Stoker 73˚ 73˚ 73˚ 73˚
Top Tube, Front 21.75" 22.5" 23.25" 23.25"
Top Tube, Rear 28.5" 28.5" 28.5" 28.5"
BB Height 10.5" 10.5" 10.5" 10.5"
Rear Axle Spacing 145mm 145mm 145mm 145mm
Seat Post Diam. 28.6mm 28.6mm 28.6mm 28.6mm
Stand Over, Front 29.8" 30.75" 31.65" 31"
Stand Over, Rear 27.25" 28.35" 29.15" 27"

The robusta appears to be 28.6 From the web page:

I believe you'll find that in the more detailed specs (http://www.co-motion.com/pdf/tandem_specs.pdf)the Robusta, Supremo & Macchiatto use 28.6mm Alpha Q Pro carbon seat posts with shims, i.e., the seat tubes are still sized for a 29.8 seat post.

True. It is shimmed going into the frame. However, for the purpose of fitting a stem on the seatpost, a 1 1/8 stem fits on with no shim.

True. It is shimmed going into the frame. However, for the purpose of fitting a stem on the seatpost, a 1 1/8 stem fits on with no shim.

Agreed.... just driving home the point that it's hard to assume or to be sure just what size seat post anyone might have without actually checking what's sticking out of a given frame. Older Robusta and Supremo frames would have come fitted with the 29.8 Wound-Up carbon seat posts instead of the Alpha Q models.

True. It is shimmed going into the frame. However, for the purpose of fitting a stem on the seatpost, a 1 1/8 stem fits on with no shim.

With a 28.6 seatpost you were very fortunate. I've been dealing with the 29.8 seatpost and trying to find the best overall solution for stoker stem selections.

So this leads to the next question, since QBP and no one else seems to offer a 29.8 to 28.6 seattube shims, I wonder if Co-Motion will sell them without the rest of the bike?

PK

With a 28.6 seatpost you were very fortunate. I've been dealing with the 29.8 seatpost and trying to find the best overall solution for stoker stem selections.

So this leads to the next question, since QBP and no one else seems to offer a 29.8 to 28.6 seattube shims, I wonder if Co-Motion will sell them without the rest of the bike?

PKI could use one of those too along with an alloy seatpost in 28.6 to match the fixed stoker post. I searched once a few months ago and came up dry on both.

With a 28.6 seatpost you were very fortunate. I've been dealing with the 29.8 seatpost and trying to find the best overall solution for stoker stem selections.
PK

Our Burley has 27.2 seatposts shimmed to 29.8. To fit the 1 1/8" stem I filed a 27.2-29.8 shim down to 27.2-28.6 and cut it to length. Took a while to file and sand it but it worked out fine in the end.

Our Burley has 27.2 seatposts shimmed to 29.8. To fit the 1 1/8" stem I filed a 27.2-29.8 shim down to 27.2-28.6 and cut it to length. Took a while to file and sand it but it worked out fine in the end.

I agree it can be done with a 29.8 to 27.2 seatpost shim to fit a 27.2 seatpost to the frame and then shim a stem from 28.6 to 27.2.

Someone else also suggested obtaining the shim with appropriate wall thickness of .6mm and install it with a slight force fit to allow a 29.8 to 28.6 to be utilized.

The 28.6 seatpost does not seem to be a problem, Thomson offers them. The 28.6 (1 1/8) stem is certainly a non issue.

There are several ways to get there, just deciding which route to take.

PK

At this point I'm leaning towards a custom fixed length stem rather than shim twice. More expensive but cleaner build.

With a 28.6 seatpost you were very fortunate. I've been dealing with the 29.8 seatpost and trying to find the best overall solution for stoker stem selections.

So this leads to the next question, since QBP and no one else seems to offer a 29.8 to 28.6 seattube shims, I wonder if Co-Motion will sell them without the rest of the bike?

PK

Tandem East has a 29.8 to 28.6 shim listed for $12. I'm not sure that it is in stock.

Thanks for the information. Two days ago, after reading here about some Co-motions having a seatpost shim in the size of 29.8 / 28.6, I gave Co-motion a quick call. I inquired and they said that I could get one, so the shim was ordered along with some other small things.

Our setup is fine for now. I'm gathering parts to make some changes, hopefully January will see some toy money to gather the few remaining parts.

Plan will be to go with Thomson seatposts, 29.8 rear / 28.6 front. Plus a few other things to make the bike better for the stoker on longer rides. This should give a lot of possibilities for stoker stems in fixed lengths.

Thanks
PK

While it wasn't my first choice, I'm leaning more towards running a pair of 27.2 seat posts and going with the 29.8 / 27.2 shims to fit the posts to the frame. I'll then use a 28.6 / 27.2 shim, trimmed to match the stokers stem, and go with this to fit the stem to captains seatpost. This also opens up many more choices for seatposts and stems. This is good for my team as I can swipe the Syncros ti posts from two other bikes we have and go with a Syncros setup of posts and captain stem that is kind of period correct for our Y2K bike.

The other option is to keep it as is, but as this post started out...saving grams.

PK

If anyone followed this topic and needs a Co-Motion oem shim to fit a 29.8 frame with a 28.6 (1-1/8") seatpost that is able to accept a 1 1/8" stem, I have a new unused one I can part with.

We got another Co-Motion that fits us better, I'm able to comfortably use the oem adjustable stoker stem, so this shim is not a route I plan to take any longer. If anyone is interested I'll part with it cheap, $5, plus some slow US Postal Service to the lower 48.

Thanks
PK