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  1. #1
    Newbie
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    North end of Long Beach peninsula, sw Washington state
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    Trek 4300 Trek T100 Giant OCR-C3
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    New to Forums with question!

    Hi everyone! My wife and I used to tandem with an ill - fated GT Quatrafoil. Sadly we gave it to a collector friend and moved away. Never got encouragement from dealers over ordering 650B components -- at the time they were available in Australia but they didn't follow up and give me prices or timelines, so I stopped pushing the issue.
    Last week we rejoined the community in that we were able to find a 1994 unused Trek T100 in the correct sizing in pristine condition. I am going over all of the systems carefully, especially to avoid corrosion, as we are 7 blocks from the Pacific Ocean. All of the components are identical to our GT's except I don't remember the stoker cranks as 175 mm. Might have been, not sure. The previous owner handed it over to us with new Specialized Flak Jacket tires, and they do look bombproof. I am excited, but the weather for once appears to be ready to return to its usual patterns, unfortunately. That's okay -- we need to replace the fresh water "lens" we lost during the long, hot draught. And the new tandem will help us witness the lens returning. We will have plenty of opportunity during the winter to "test" my maintenance and check the marsh nearby.
    We had a shock seat post for the stoker, and I want one again. We are 10 years older! I wonder if anyone here has an idea how I might determine a correct seat post and shim combination for the tandem. I see the seat posts on the new Trek are indicated as 29.8. Either the choices are lesser now, or the tubeset used in the GT was more in line with available seat post sizes -- I think we used a 30.8 mm. post or something like that. This time, I will try a 27.2, but am unsure just what shim combo to use. Anyone have stories of what worked for you?
    I have found the Trek to be stiffer than the GT, and about 2 pounds lighter, incidently. I had also forgotten about the wider turning radii! Dan

  2. #2
    Senior Member
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    Kingston, Ontario
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    Norco Bigfoot, Miyata 110, Giant TCR Advanced 0
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    For seat posts see what's in the bike now 29.8 and buy that size or smaller. If it is smaller you need a shim for both sizes.



    I.e. If you use a 27.2 post get a shim that is 29.8 to 27.2. That's all there is to that. Just make sure you can get the proper shim before buying a post. Some shims can be impossibly thin.

  3. #3
    Senior Member
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    If you're buying a suspension post, a 27.2 is a common size. It's easy to get seatpost shims in a wide range of sizes:

    Problem Solvers

  4. #4
    Nigel nfmisso's Avatar
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    Mar 2011
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    1980s and 1990s steel: CyclePro, GT, Nishiki, Schwinn, SR, Trek........
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    We have a '94 Trek T50 (same frame as the T100 & T200). When we first got it a few years ago, it has a suspension seat post. My wife decided that she did not like the suspension seat post, after trying rigid......

    Sorry, it did not stayed with us after the last move, otherwise I'd send it to you.
    Nigel
    Mechanical Design Engineer

  5. #5
    Senior Member
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    Quote Originally Posted by mtseymour View Post
    If you're buying a suspension post, a 27.2 is a common size. It's easy to get seatpost shims in a wide range of sizes:

    Problem Solvers
    You just need to make sure that it is not bigger than your existing seatpost. But I agree.

  6. #6
    Senior Member
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    Feb 2010
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    Philadelphia area, Pa., USA
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    Santana Cabrio triplet, Santana Fusion S&S tandem, Co-Motion Mocha S&S tandem, Co-Motion Pangea S&S, Co-Motion Nor'wester S&S, C'dale F2000
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    29.8 is a common seatpost size for tandems, especially Santana and Co-Motion. Keep a look out on Ebay and I'm sure you'll find one. Alternately, you just need a 29.8 to 27.2 shim, also readily available either online or your LBS can order you one.

    One piece of advice is to stay away from the cheap suspension posts. They generally don't work very well, and either compress right away or give you a "pogo-stick" sort of experience. Make sure what you get has adjustable preload, and also preferably adjustable/replaceable suspension parts (elastomers or springs, etc.). "Tamer" is a well-regarded brand, which is used as OEM on Santana tandems. RockShox also makes a decent one. There are other very high-end suspension posts in the MTB world, but they are overkill for tandems IMO.

    I may have a Santana/Tamer suspension post in my parts box that we took off one of our tandems. If so, I'll let you know and post it for sale here. My wife prefers a non-suspension post because of knee issues.
    Last edited by briwasson; 11-23-15 at 10:54 AM.

  7. #7
    Senior Member zonatandem's Avatar
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    On all of our tandems (5) in the past 40+ years we have never needed/wanted a suspension seatpost.
    Attached Images Attached Images

  8. #8
    WPH
    WPH is offline
    Senior Member WPH's Avatar
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    Perth, Western Australia
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    2015 Apollo Syncro tandem, 2006 Scott CR1 SL (still a beastie race bike), 1993 Trek T200, 2006 Fuji Absolute Le, 2000 Thorn Club Tour
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    Better post a picture of your new bike. In fact several pictures, some on this thread, some on the 'pictures of happy tandem teams' thread and one or two on the 'what does your tandem weigh' thread.

    The stoker cranks on my 1993 T200 are 175mm.

    We have tried a Thudbuster ST on the T200 but it has always slipped in the shim. Have tried 3 or 4 shims of different brands and materials, plus carbon anti-slip paste, plus roughing the contact surface, but no luck, even when the rear QR is done up scary tight. Never heard of anybody else having this problem )-:

    But anyway my current stoker is happy on the rigid seatpost and I have found some economically priced 29.8mm models online (the stoker seatpost was corroded into the frame when we bought the bike, it was cut out).

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