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  1. #1
    PMK
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    Co-Motion stoker fit

    I have to ask. We have a 2000 Co-Motion. The size is a 21/18 (small). We bought the bike used and really enjoy it.

    Here's the crisis, it seems the newer Co-Motions built several years after ours have a 28.5" toptube. Ours has a 27" toptube. Per their specs all stoker toptubes are the same length for all sizes. Even if we were to get the next larger frame (unless it was a more current frame) it would still have the same stoker toptube length.

    My wife/stoker is still finding the length to short. She is 5'6" on a good day. The setup has a stem that is 80mm long, and a seatpost with rear offset of around 15mm. Her fit of saddle height and knee over spindle are good, she wants the bars forward.

    Tonight for grins I installed the Thudbuster off the mountain tandem, we didn't ride but it gained some length. It did move her knee back slightly.

    So as I mentioned, I have to ask, is there any one else with a Co-Motion of similar vintage, that has a stoker that is finding the rear to small. Short of riding more upright, how are these bikes fitting taller stokers?

    PK

  2. #2
    SDS
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    It has occurred to me, that if you have a tandem that has bottom bracket spacing that is too short (i.e., a stoker top tube of 27"), that it might be possible to extend that by adding longer tubes with S&S couplers. The possible advantages would be 1) a perceived upgrade to the bike, 2) reduced cost compared to buying a whole new frameset, and 3) the preferrred fit of the stoker.

    Best fit seems to be single bike fit (the horizontal distance between the center of the seatpost and the center of the handlebars) plus at least eight more inches, so for a stoker with 23" seatpost to handlebar spacing, you would want bottom bracket spacing of at least 31".

    I have a tandem with 37" bottom bracket spacing, which in almost all cases makes using Profile Airstryke aerobars possible for the stoker. There's plenty of room to stand up and move forward just as would normally be done on a single bike, and the aerodynamic drag drops noticeably when the stoker is on the aerobars.

  3. #3
    Senior Member ftsoft's Avatar
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    Quote Originally Posted by PMK View Post
    I have to ask. We have a 2000 Co-Motion. The size is a 21/18 (small). We bought the bike used and really enjoy it.

    Here's the crisis, it seems the newer Co-Motions built several years after ours have a 28.5" toptube. Ours has a 27" toptube. Per their specs all stoker toptubes are the same length for all sizes. Even if we were to get the next larger frame (unless it was a more current frame) it would still have the same stoker toptube length.

    My wife/stoker is still finding the length to short. She is 5'6" on a good day. The setup has a stem that is 80mm long, and a seatpost with rear offset of around 15mm. Her fit of saddle height and knee over spindle are good, she wants the bars forward.

    Tonight for grins I installed the Thudbuster off the mountain tandem, we didn't ride but it gained some length. It did move her knee back slightly.

    So as I mentioned, I have to ask, is there any one else with a Co-Motion of similar vintage, that has a stoker that is finding the rear to small. Short of riding more upright, how are these bikes fitting taller stokers?

    PK
    Just curious-- what is the distance from saddle tip to the middle of the handlebars on the tandem vs. your stoker's single bike?

    Frank

  4. #4
    Senior Member zonatandem's Avatar
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    Or a custom shorter stoker stem could help + use of cowhorn stoker bars . . .
    But then you could end up with capt's quads hitting her hands.
    $&$ retrofitting would an expensive alternative.
    Many stokers (mine included) prefer a bit more upright position.

  5. #5
    PMK
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    Quote Originally Posted by SDS View Post
    It has occurred to me, that if you have a tandem that has bottom bracket spacing that is too short (i.e., a stoker top tube of 27"), that it might be possible to extend that by adding longer tubes with S&S couplers. The possible advantages would be 1) a perceived upgrade to the bike, 2) reduced cost compared to buying a whole new frameset, and 3) the preferrred fit of the stoker.

    Best fit seems to be single bike fit (the horizontal distance between the center of the seatpost and the center of the handlebars) plus at least eight more inches, so for a stoker with 23" seatpost to handlebar spacing, you would want bottom bracket spacing of at least 31".

    I have a tandem with 37" bottom bracket spacing, which in almost all cases makes using Profile Airstryke aerobars possible for the stoker. There's plenty of room to stand up and move forward just as would normally be done on a single bike, and the aerodynamic drag drops noticeably when the stoker is on the aerobars.

    I just measured, out Bottom Bracket to Bottom Bracket dimension is 27.5 inches.

    As for S&S, I would prefer getting another bike, and sell this one. If I went with S&S couplers, I would prefer them done during the original build. Probably less headache. A good idea.

    Thanks
    PK

  6. #6
    PMK
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    Quote Originally Posted by ftsoft View Post
    Just curious-- what is the distance from saddle tip to the middle of the handlebars on the tandem vs. your stoker's single bike?

    Frank
    You had to ask that magic question.

    I had a bunch of notes about the height, bar to nose of saddle dimension and so on and can't find them.

    These notes were done to fit the mountain tandem to her. The mountain tandem was also short. I believe the thudbuster helped a lot since it swings rearward as it works, so just static sag moves the saddle aft.

    If memory serves me correct, the length difference is 1 inch. This is single mountain bike vs mountain tandem.

    This why I'm considering selling this bike and getting a newer one. There's an additional 1 1/2 inches. I just don't understand then, how the riders setup their position on these shorter early frames. As I mentioned, all production frame sizes of the same model have the same dimensions for the stoker.

    PK

  7. #7
    PMK
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    Quote Originally Posted by zonatandem View Post
    Or a custom shorter stoker stem could help + use of cowhorn stoker bars . . .
    But then you could end up with capt's quads hitting her hands.
    $&$ retrofitting would an expensive alternative.
    Many stokers (mine included) prefer a bit more upright position.
    I've been playing with stems and bars. Just testing without riding, I installed a 50mm stem. This added 30mm to her existing stem (existing stem is 80mm). This would have been too easy, but as you mentioned, now my legs have hard contact.

    I tried several sets of bars. Our current setup uses a flat mountain bar with bar ends. For testing, I tried a 44cm drop bar and what is I believe the original stoker bull horn bar.

    I ordered the shortest stem I dare try, 65mm. I'll give that a shot once it arrives.

    Thanks
    PK

  8. #8
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    I didn't know you could buy 30mm and 50mm stems. That would place the bars way underneath your saddle. Doesn't your stoker hit your back in addition to your legs hitting the bars?

  9. #9
    SDS
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    If you do get to the point of getting a new tandem, keep in mind that some manufacturers charge only a little or perhaps nothing at all for custom frame dimensions, i.e., longer-than-standard bottom bracket spacing.

  10. #10
    PMK
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    Quote Originally Posted by rmac View Post
    I didn't know you could buy 30mm and 50mm stems. That would place the bars way underneath your saddle. Doesn't your stoker hit your back in addition to your legs hitting the bars?
    I don't about 30mm. but in regards to the 50mm, the 65mm I just ordered, and the 80mm now installed, these are all 1 1/8 regular stems. Not adjustable types. But I will add, the current 80mm stem, is truly an angle adjustable 1 1/8 stem of 105mm@ 0 degrees. With it tilted full up making it 80mm @ 40 degrees.

    As for the bars being under the seat rails, yes they are. Stoker doesn't quite hit my back, and yes my legs do lightly hit the bars on the mountain tandem, I don't even notice it. With the 50mm stem on the road tandem, just a quick hold me up and check test found the stem was to short. I split the difference between 50 and 80 and ordered a 65mm.

    This why I keep wondering, is my stoker a freak, or was being this long not dealt with back around 2000 when this frame was built. I'm sure they had stokers of 5"6" in Y2K, I'd just like to know how they set their stuff up. I know strange, very strange.

    PK
    Last edited by PMK; 01-07-09 at 10:33 PM.

  11. #11
    Senior Member zonatandem's Avatar
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    Production tandems are set up for 'average' riders in that particular size.
    However some of us have longer/shorter arms/torsos/legs and need to find a way around that.
    Usually done by doing some fiddling around with stem lengths, saddle setbacks, etc. Other option: custom.
    Consider our dilemma: Pilot is avarage size 5'7", stoker is 4' 10 3/4" inches 'tall'.
    Our solution: custom tandem(s) for 30+ years. Distance between our BBs is 24 3/4", wheelbase 63 1/2" . So you think you've got fitting issues??!
    Our shortest wheelbase custom racing tandem (back in 1977) was 60 1/4" . . . used to wear out top of stoker's gloves with my quads! But what a great exciting ride!
    Pedal on TWOgether!
    Rudy and Kay/zonatandem

  12. #12
    PMK
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    Quote Originally Posted by zonatandem View Post
    Production tandems are set up for 'average' riders in that particular size.
    However some of us have longer/shorter arms/torsos/legs and need to find a way around that.
    Usually done by doing some fiddling around with stem lengths, saddle setbacks, etc. Other option: custom.
    Consider our dilemma: Pilot is avarage size 5'7", stoker is 4' 10 3/4" inches 'tall'.
    Our solution: custom tandem(s) for 30+ years. Distance between our BBs is 24 3/4", wheelbase 63 1/2" . So you think you've got fitting issues??!
    Our shortest wheelbase custom racing tandem (back in 1977) was 60 1/4" . . . used to wear out top of stoker's gloves with my quads! But what a great exciting ride!
    Pedal on TWOgether!
    Rudy and Kay/zonatandem

    I hear the point about wearing out stoker gloves, the mountain tandem before long will have a polished inner handlebar. But it is nice in tight singletrack, and believe it or not, one reason the stoker would not let me step us over to a Ventana ECDM. The mountain is now a good fit for both of us, and as you say a great exciting ride. The mountain is no problem on technical rides as she's moving or boucing around abit.

    I can see your need for special sizing. As I mentioned be somewhat stymied with her fit, as at 5'6" with a 32/33" inseam, I can't figure out why she needs this room. In the end it doesn't matter, I just need to get her comfortable.

    I'm really leaning towards another bike or frame, then sell this one.

    My last apparent options are trying the 65mm stem, and or seriously trying the thudbuster for a ride or two. I just would like her more comfy and not get her ergos where her legs work best, to far whacked out.

    Thanks
    PK

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