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Thread: Sizing

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    Sizing

    This is probably a stupid question but why is the frame size of the tandem all that important. Could a small frame work for pretty much any team. By changing stems, adding a stem riser and adjusting seats isn't it essentially possible to get a frame that works for anyone? It looks like rear top tubes are all the same and I'm thinking that's the idea with the co-motion periscopes (still offered in small and larger). I would guess the reason not to do this is control and stearing but how can you tell if it's unsafe (before you crash). What else am I missing.

    I'm saying this because frames that are "too small" for us appear often while the XL and the Jumbos are a bit more rare. Read between the lines as there is a small co-motion that is a great deal but we currently ride a Cannondale Jumbo and I'm trying to convince my wife that we should get it.
    Last edited by act0fgod; 08-18-10 at 06:47 PM.

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    just another gosling Carbonfiberboy's Avatar
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    I'll let the more knowledgeable tell you why, but when I was searching for our small CoMo, I found large frames much more common than small. Keep looking. And say how tall you both are.

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    I'm 6'1" and my wife is 5'7".

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    hors category TandemGeek's Avatar
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    Quote Originally Posted by act0fgod View Post
    This is probably a stupid question but why is the frame size of the tandem all that important. Could a small frame work for pretty much any team.
    The front of the tandem needs to fit the captain, in the same way that a single bike needs to fit its rider... No difference and, in some respects, a proper fit on a tandem is more important since the task load on the captain is higher than a single bike rider.

    Quote Originally Posted by act0fgod View Post
    By changing stems, adding a stem riser and adjusting seats isn't it essentially possible to get a frame that works for anyone?
    Yes, it is 'possible' to make a small bike's touch points mimic the dimensions of a larger bike: BikeFridays and Brompton folding bikes prove this point. So, if you can get your reach and the height of the handlebars to fall in line with your normal riding position, you should 'technically' be able to ride the bike without creating a fit problem. Now, as to how that bike might 'feel', all bets are off as there's a point of diminishing return that comes with riding bikes that are just a little bit too big or too small. However, you won't know if you've pushed the limits a bit too far until you put a few miles on a bike that's been 'tweaked' to fit.

    From personal experience, too small is better than too big, but TOO SMALL just won't feel right at at 6'1" you're a good deal over even Co-Motion's generous size range for a small frame, e.g., 5'10". The Medium's top-end of the size range is, coincidentally 6'1".


    Quote Originally Posted by act0fgod View Post
    ... Read between the lines as there is a small co-motion that is a great deal but we currently ride a Cannondale Jumbo and I'm trying to convince my wife that we should get it.
    Personally, I think you're over-reaching, so to speak. However, if you're really enamored with it see if you can take it for a test ride -- or take any other small-size Co-Motion for test ride -- and see how it feels. If neither of those things are possible, just go take a test ride on a single comfort bike that's sized like the Co-Motion -- same top tube / reach and relative head tube height -- and see how that feels: most of these comfort bikes come with VERY adjustable stems that would allow you to raise and move the bars forward.

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    With a smaller frame you might get toe overlap with the front tire.
    With a real long stem the bike will respond differently to steering input.
    Adding hardware to move the bars could made for a less solid connection. I have an adjustable stem that has too much flex for me.
    A shorter frame will put more weight on the front wheel, but that won't matter with the long wheelbase of a tandem.

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    just another gosling Carbonfiberboy's Avatar
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    And on a small tandem, the stock crank lengths might be less than optimal for you.

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    Well you've all agreed with my wife so there is still a coupled co-motion that is roughly 5 years old in Flagstaff AZ for only $2200...don't think it will be available for long at that price.

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    hors category TandemGeek's Avatar
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    Quote Originally Posted by Carbonfiberboy View Post
    And on a small tandem, the stock crank lengths might be less than optimal for you.
    Sadly, most production tandems come with the same size cranks regardless of the frame size (175/170), in the same way many production tandems from a given builder will also have the same stoker top tube length regardless of frame size designation. There are some dealers who have been able to accommodate requests for different sizing, but it's the exception and not the rule that such a request is made.

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    just another gosling Carbonfiberboy's Avatar
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    Quote Originally Posted by TandemGeek View Post
    Sadly, most production tandems come with the same size cranks regardless of the frame size (175/170), in the same way many production tandems from a given builder will also have the same stoker top tube length regardless of frame size designation. There are some dealers who have been able to accommodate requests for different sizing, but it's the exception and not the rule that such a request is made.
    Ah, thanks. And all this time, I thought ours was a mistake, or some weirdness of the original owners. I understand the same size stoker compartment, but not the cranks.

    Checked out the bike in question, nice bike, always wished ours was coupled, but ours is a slightly higher spec and we love it. Can't afford two.

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    You may be limited by the top tube length for the captain on a small frame. The C'dale Jumbo has a long top tube (around 60 cm). If this is about right for you there is no way you will get by with a top tube that is 6cm or more shorter and also a steering head that will be significantly lower.

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    We just bought our tandem after a lengthy search and after spending quite a bit of time on the sizing issue. Bottom line: size matters! As everyone has mentioned.. Here are some key lessons from our experience --

    - Top tube matters more than seat post length. You have more range in seatpost adjustment (4-6"). Not as much in compensating for top tube size. Make sure you shop for the correct top tube length for the captain. Stoker has a bit more flexibility with this dimension, since most tandems have reach-adjustable stoker bars, but seat tube length and standover also matter for both you and the stoker.

    - Frame sizes are not standardized across manufacturers. E.g. A Co-Motion Large is not the same geometry in terms of the rider-fit dimensions as, say, a Santana Large. Become familiar with the actual frame specs for the bikes you're shopping.

    - I think it's largely irrelevant, or at least misleading, to judge your own fit on a bike in comparison to someone else' height. Just because the seller is 6'1" doesn't mean the bike will fit you. It could be a poor fit for him/her, and as well your body proportions are almost certainly not the same as the next guy's. I'm 6'3", and thought I needed an XL Santana. I rode one being sold by a guy 6'1" and found the bike was impossibly large for me.

    - I went to my local bike shop and paid them $50 to fit me and it was money well spent - I would have wasted that much on gas, going to look at a tandem 3 hours away. I also re-fit myself (using the dealer's expertise) to my current personal road bike. After that process was complete I had a much clearer understanding of both my seat tube and top tube length requirements.

    Good luck with your search, and keep asking questions!

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    Quote Originally Posted by Carbonfiberboy View Post
    I'll let the more knowledgeable tell you why, but when I was searching for our small CoMo, I found large frames much more common than small. Keep looking. And say how tall you both are.
    That's ironic; we were looking for a large, so of course we found smalls and mediums to be the more commonly available size! I think there is a Murphy's Law to be discovered in these occurrences.

  13. #13
    Senior Member CHAS's Avatar
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    A stem that is too long for a frame will put the rider OTB too often. Been there, done that.
    OTB=over the bars
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  14. #14
    Senior Member zonatandem's Avatar
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    Folks have presented the proper case for proper fit for 2 people.
    Tandems are like shoes . . . the right size matters! So wear sandals as fit is not as crucial . . .
    Yes, you can have a make-do fit in a tandem also.
    We've owned 4 custom tandems; pilot 5'7", stoker 4' 10 3/4".

    Pedal on TWOgether!
    Rudy and Kay/zonatandem

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