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Thread: "Short" tandems

  1. #1
    Dharma Dog lhbernhardt's Avatar
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    "Short" tandems

    Well, being a contrarian by nature, and having put many thousands of kilometers on the nearly-vintage Kuwahara tandem in the past couple of years, I am coming to the conclusion that the biggest boost to tandem popularity in the past 30 years - namely, the stretched rear compartment pioneered & promoted by US tandem builders - is oversold. Having attended a couple of tandem rallies in the Pac Northwest, it seems to my contrarian eyes that a lot of rear frame space is wasted. The stoker seems to have too much room.

    This wouldn't be an issue, except that the longer rear compartment comes at the expense of a longer wheelbase, which I think most would agree is detrimental to "sporty" handling. Maybe this really isn't an issue, as I have heard that Co-Motion has the handling paradox resolved in its frame geometry.

    Anyway, just as a mind exercise, I wonder how a "short" tandem would fare? By "short," what if we REALLY shortened the rear compartment, moving the stoker right up behind the driver (much like on a motorcycle). The stoker's stem would be flipped around to the front of the captain's seat post and much longer, so that it would rise up between the captain's legs. The stoker's bars would then be placed in front of the pilot and the stoker would reach around the captain to grab them. The two cranksets might have to be so close together that pedaling would have to be in phase to avoid conflict. If the tandem crashed, the captain would basically be trapped in the stoker's bars! (Or maybe protected by them...). In any event, the wheelbase could be considerably shorter, resulting in faster handling, and the stoker may not feel the bumps as intensely.

    I wonder if this has been attempted/mentioned/designed?

    - L.

  2. #2
    hors category TandemGeek's Avatar
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    Quote Originally Posted by lhbernhardt
    The stoker seems to have too much room.
    How much time have you spent on the back of a tandem stoking?

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    I am a big proponent of the extra long stoker compartment. I learned it also from Erickson and R & E cycles.

    I think the first supposition that you are making, that is a tandem would handle more "sporty" if it was 3 to 4 inches shorter in its wheelbase is not completely accurate.

    IMHO, fit supersedes all other bike design considerations. A proper fitting team will produce the most amount of power available with the most comfort. The frame must be designed around this. So even though it may look like there is a lot of room available, some of that room may be used when teams stand or allow for more aerodynamic positioning of the stoker without interference from the stokers handlebars and such.

    Also consider that handling is multifaceted. The overall length of a tandem only affects the turning radius of a vehicle to a small degree (exactly the extra length *PI) so this case if the tandem was 3 inches longer then I will have increase theoretical turning radius by about 10 inches. This has even less effect at speed. As long as the tandem is ridged enough to handle the extra length well everything works well.

    I have considered as a design exercise an extremely short "donkey back" tandem. I see it for track use and such where the stoker pedals directly into the rear hub and the rear wheel is right underneath the rider. Even with a generous cockpit this would make for a tandem that was not a whole lot longer than a single and might allow for faster positioning in tandem track racing.

    Dave Bohm
    Bohemian

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    hors category TandemGeek's Avatar
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    Quote Originally Posted by dbohemian
    I have considered as a design exercise an extremely short "donkey back" tandem.
    Something along the lines of the infamous Corima tandem built for Chenoweth when he was "managing" and racing on the EDS squad?


    http://images.velonews.com/images/news/1680.1687.t.jpg
    Last edited by TandemGeek; 06-18-07 at 10:36 AM.

  5. #5
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    Quote Originally Posted by TandemGeek
    How much time have you spent on the back of a tandem stoking?
    +1 on that

    Im in the back and there is not enough room, and to have more, I would have to go custon. not off the shelf tandem could give both of us the correct sizing.

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    Stokers want more room

    I've piloted 3 tandem lengths and from a captains POV,the shorter tandem is less of a wrestling match.

    However,the stoker greatly preferred the longest bike...

    I'm guessing/betting that one of the most common options on custom tandems is a longer stoker TT/distance between BB's. They can stretch out and get low and I'm quite sure that being farther downwind from me on a hot day would be nice...
    no signature

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    Senior Member zonatandem's Avatar
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    Doesn't look very comfortable . . .

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    Senior Member zonatandem's Avatar
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    short tandem?

    here's the picture . . .
    Attached Images Attached Images

  9. #9
    Senior Member zonatandem's Avatar
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    Shortest wheelbased tandem we have owned/ridden/designed had 60 1/4" wheelbase . . .
    Very 'petite' stoker, big toeclip overlap, bent rear seattube with extremely short chainstays (so short, we had to deflate rear tire to remove wheel). Pilot's quads hit stoker's gloved hand if she was on the hoods . . . but not in the drops. In extreme tuck position, her helmet was against pilot's back. Stoker bars/stem were in the traditional position.
    Quick/fast/light racing tandem . . . but it fit. We put 64,000 miles on that tandem, and yes, we loved it (but that was in younger hell-bent days!).
    Contrary to your belief the shorter tandem was harsher ride for stoker (as she really sat over that rear wheel) than our later longer tandems which had/have a 63 1/2 wheelbase.
    Pedal on TWOgether!
    Rudy and Kay/zonatandem

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    Hey Zona, scary that Sears would have the answer to the OP.
    NewbieIATandem
    Big Team on Trek T900

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    Ihbernhardt....I think you need to think your idea over a little more. I see some serious "issues". If the two riders are as close on you suggest... as on some motorcycles, how does either person pedal. There would not be enough room for them to move their legs in the full circles needed for pedaling. Standing on hills ... or to just get off the seat, would be totally out of the question. How would you even get on the bike and get moving? The stoker can't hang onto anything until the capton gets on. It sounds very awkward.

    When I had an off-road tandem custom made. We wanted it as short as we could get it... to fit through our tight and twisty trails. Yet having the bike fit correctly ... had priority to that. The wheel base was slightly shorter [maybe an 1" or so] but the bike fit like a glove. It handled great. Of course it did not handle in the woods like a single bike... but there are some things in physics you can't get around. Besides we enjoyed the challenge of getting a "beast" of it's size through the woods.

    glenn

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    hors category TandemGeek's Avatar
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    Hey, there's always the "Love" bike, or as it's now known the "Buddy Bike"
    http://www.buddybike.com/

    Seriously though, I think you need to take a contemporary performance tandem like a Co-Motion for a test ride to scratch your itch. The Kuwahara is well off the front in terms of where materials and frame design have gone since they were produced.

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    close, but technically a "donkeyback" has the stoker putting power directly into the rear hub and is also directly over the rear wheel. Kind of like this:

    http://images.google.com/imgres?imgu...icial%26sa%3DG

    To make one with gearing would be a difficult engineering issue, fixed would be a little easier.

    Sorry that is the best picture I could find quickly. I have seen some very old ones up close.

    That one will most likely stay a conceptual idea. Can't see that there is a market for such a thing.

    Dave

  14. #14
    rebmeM roineS JanMM's Avatar
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    Quote Originally Posted by zonatandem
    here's the picture . . .
    Reaching for the bars in front of the captain's seat would put the stoker's face just about in the captain's.....................................................lower, lower, lower back region.

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    Elite Rider Hermes's Avatar
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    It is an interesting observation. I suggest that you spec out a short wheelbase tandem, have Dave Bohemian build it for you and see how it works. If you cannot find any stokers, you can hang it on your wall as a piece of art and it will not take up much room.
    "Insanity: doing the same thing over and over again and expecting different results." Einstein

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    Radfahrer Rincewind8's Avatar
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    Quote Originally Posted by zonatandem
    here's the picture . . .
    For some reason I have the feeling the bike was not assembled as intended by the manufacturer. I mean how would the captain of this bike pedal without hitting the stoker handle bars?!?
    TH 1.81 (133kg*62)

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    Quote Originally Posted by Rincewind8
    For some reason I have the feeling the bike was not assembled as intended by the manufacturer. I mean how would the captain of this bike pedal without hitting the stoker handle bars?!?
    Check it out, it is on the Sears website for $175 or there abouts. If you can do your own setup etc. maybe Sears is OK, but except for very light use a $175 tandem where the marketing photo is not even setup correctly...

    I had thought about buying this bike as a second light duty bike but once looked at it more closely and yep, it's obviously setup incorrectly.
    NewbieIATandem
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    Radfahrer Rincewind8's Avatar
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    Quote Originally Posted by NewbieIATandem
    Check it out, it is on the Sears website for $175 or there abouts. If you can do your own setup etc. maybe Sears is OK, but except for very light use a $175 tandem where the marketing photo is not even setup correctly...

    I had thought about buying this bike as a second light duty bike but once looked at it more closely and yep, it's obviously setup incorrectly.
    Oh, I'm not in the market for a new tandem, nor would I buy that one. It's just funny (or maybe sad) that they use a photo with the handlebars set up incorrectly.
    TH 1.81 (133kg*62)

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    Quote Originally Posted by Hermes
    It is an interesting observation. I suggest that you spec out a short wheelbase tandem, have Dave Bohemian build it for you and see how it works. If you cannot find any stokers, you can hang it on your wall as a piece of art and it will not take up much room.
    Well, I am willing to give it a shot, just as long as the stoker fits correctly

    Many early tandems were built super short. I think the concept may have died do to the difficulty of incorporating gear sets into the designs and the fact that you could not use standardized componenty.

    IMHO bike designs are almost never optimized nor does it mean that because something does not exist now, that it did not have great merit previously.

    Dave Bohm

  20. #20
    Co-Mo mojo
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    Quote Originally Posted by dbohemian
    Many early tandems were built super short.
    I am on the road (figuratively), but when I get home tomorrow I'll try to find and post a picture of a friend's track tandem from the 1968 Olympics. The picture has Peter on the bike with no stoker -- it almost looks like a single. I was the stoker for a few months on an early 1970s Paramount and my most important recollection was how tight the fit was (ok, the bike was probably too small for a 6'2" stoker with long legs).

    Our 1977 Gitane had a bit more room, but nothing like the luxury of our CoMo Speedster. My stoker would stick to her single if the only choice was a short frame. In this case, the change in design made regular tandeming possible for us. YMMV....

  21. #21
    Senior Member zonatandem's Avatar
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    Yup, Paramount built a 'short' tandem with drastically bent rear seattube back in the 70s. Gitanes were a bit longer. Did see a Gitane with bent rear settube. Most tandems of that time period were shorter than the current average of around 69" wheelbase.
    Nothing wrong with a 'short' tandem, as long as it fits the riders properly.
    That's Sears tandem, with erroneous stoker bar setup, of course was done by an 'expert' Sears certified assembler . . .
    Pedal on TWOgether!
    Rudy and Kay/zonatandem

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    Elite Rider Hermes's Avatar
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    Quote Originally Posted by DBC Steve
    I am on the road (figuratively), but when I get home tomorrow I'll try to find and post a picture of a friend's track tandem from the 1968 Olympics. The picture has Peter on the bike with no stoker -- it almost looks like a single. I was the stoker for a few months on an early 1970s Paramount and my most important recollection was how tight the fit was (ok, the bike was probably too small for a 6'2" stoker with long legs).

    Our 1977 Gitane had a bit more room, but nothing like the luxury of our CoMo Speedster. My stoker would stick to her single if the only choice was a short frame. In this case, the change in design made regular tandeming possible for us. YMMV....
    Sorry for hijacking this thread for a moment but DBC Steve, will we will see your tandem in a local TT race? Did you race at Dunlap?
    "Insanity: doing the same thing over and over again and expecting different results." Einstein

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    Elite Rider Hermes's Avatar
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    Back to topic...I think the advances in material's strength to weight ratio allows manufacturers to lengthen bikes without turning it into noodle.

    Here are two tandems that go in the other direction in pursuit of speed. One would need a miracle to make a u turn around a cone on a narrow road.



    "Insanity: doing the same thing over and over again and expecting different results." Einstein

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    The fastest mixed tandem team at the last Paris-Brest-Paris used a 50 year old French tandem. No bent seat tube but a super-short rear top tube. It didn't seem to slow them down and it must have been comfortable enough (1200 km in just over 2 days)

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    The older French tandems were very nice.

    The reason old tandems were so short was that the available tubing was all sourced from singles. If you cut off the absolute bare minimum you ended up with stoker top tubes similar to what old Herse's and similar bikes had.

    I don't think it necessarily held back riders but I do think it was far from optimum concerning stoker fitting.

    The long stoker compartment (for a large majority of riders but not all) is the single biggest improvement in tandems in the last twenty years. I believe that strongly in it. It is only with the advent of longer tandem specific tube sets and reasonable OS tubing to retain rigidity that this has become possible.

    Also consider that having a long stoker compartment opens up whom you can ride with. Tandem teams don't often have other stokers out for fun but it is entirely possible with longer compartments.

    Dave

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