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All American 6
07-19-07, 06:44 AM
Road Frame:
Why do some builders (Cannondale/some Santana/others) have the top tube connected to the lateral tube instead of the head tube?
What are the advantages/disadvantages?
Is this desirable?
Is there a name for this frame design?
AA6
Thanks Craiglist for selling my Burley/Piccolo in less then a week!
TandemGeek
07-19-07, 08:04 AM
Why do some builders (Cannondale/some Santana/others) have the top tube connected to the lateral tube instead of the head tube?
One of two primary reasons:
1. To provide the captain with more standover height than would otherwise be possible with a conventional, un-stepped top tube on their smaller road and off-road tandems while still providing some additional, internal bracing in the front triangle and a relatively tall head tube to support somewhat higher handlebar positioning often times favored by tandem captains. The alternative is to use a highly compact frame design similar to what's now showing up on the lateral-less (or as I prefer to call them, top (tube) less) tandems from Paketa, Calfee, Co-Motion, etc... You'll find a similar, steeply sloping top tube on most Erickson tandems.
2. To simplify the lines of a tandem's horizontal top tube to support convertible (aka. cabrio (http://www.sandsmachine.com/a_san_t5.htm)) multi-seat tandems that can be converted from two seat to three seat, four seat and/or five seat configurations. This also affords the captain additional standover height which, again, may be desireable on a multiseat tandem, as well as additional front triangle bracing. The alternative (or at least one of the alternatives) is to use an even more radical design (http://www.bikemagic.com/news/images/ib05_comotion_big.jpg).
What are the advantages/disadvantages?
Advantages: As mentioned above. Moreso when used on off-road tandems where 3" or more of standover height is desireable.
Disadvantages: Functionally, none. Aesthetically... that's somewhat subjective.
Is this desirable?
Only if you need or want more distance between the top tube and your "boys" and/or are considering a convertible multi-seat tandem. If you need a smaller size Santana or Cannondale it is what it is, unless you opt to go with a custom-framed Santana. Cannondale does not do one-offs.
Is there a name for this frame design?
I've always referred to it as a "stepped" top tube.
If you're interested in seeing just how many different ways there are to design a frame to accommodate riders of varying heights, or what a multi-seater would look like if it was designed without a continuous, horizontal top tube, take a look at a few Ventana El Conquistadors...
zonatandem
07-19-07, 01:16 PM
Standover room is the primary reason.
Here's a different aproach on our Zona tandem.
Drastically sloping top tube. Lateral blends into the downtube.
Aestethics are a personal issue . . .
Pedal on TWOgether!
Rudy and Kay/zonatandem