Originally Posted by
steelbikeguy
Is there any chance that the Schwinn tandems had short stoker top tubes because they were copying the geometry of racing tandems?
Yes I have heard that story, maybe apochryphal. The version I heard was the first Paramount tandems were made for the Rome Olympics (1960), and the only tandem event at the Oly's was Match Sprint. That's essentially a 10-second event, the part of it that matters. So comfort for long miles is not in the list of requirements.
Then (the story goes) they used the same jig made for the 1960 Oly bike to make P'mounts for sale through dealers.
I guess that story might be laughably wrong if the 1940s tandem you showed is really a Paramount. I guess it doesn't matter what they called it; the important fact is they had the ability to make tandems much earlier than 1960. The jig doesn't care if it's a Superior, Town & Country, or a Paramount.
The story could still be true, if they used a single-bike jig (or no jig at all) to make tandems previously, which is do-able, just inefficient. And only made a dedicated tandem jig in the buildup for the '60 Oly's. Certainly you don't need a jig to make a tandem; The Taylor bothers (Jack Taylor) made hundreds, maybe thousands? with just tubes laid on firebricks, with a heavy weight laid on to to hold the tubes down! Alignment checked by holding the frame up towards the window and squinting.
I recall photos of track tandems where the stoker had his chin in the captains back, which makes me think the stoker's top tube must have been relatively short.
I don't have one of those photos handy, but I do have pics of a 1940's track tandem that was displayed at the 2016 Classic Rendezvous gathering. Maybe one of you folks can eyeball it and judge whether the stoker's top tube is as short as the 1970's Paramounts?
and a second topic... I like the extra set of stays, which I assume are to help stiffen up the rear end?
This leads to the next topic... would the short stoker top tube be used just to stiffen up the frame, or is it more to make the bike more maneuverable or aerodynamic?
Yes and yes, all of the above. Except any stiffening of the rear triangle from those mid-stays on the 1940s bike is not going to be detectable, they are poorly placed to resist the stresses on a rear triangle. If those stays continued all the way up like on a mixte or on the red Paramount that started this thread, then they can "pull their weight" so to speak. But the ones on the '40s bike are just extra ground-hugging mass IMHO.
EDIT: ooh and notice the tiny chainrings used for the timing chain on the '40s bike; definitely suboptimal for a sprint bike. Chain tension is inversely proportional to chainring size, all else being equal, so if you used rings twice as large, you'd have literally half the chain tension from the cap'n sprinting. There's a lot of frame flex caused by that chain tension, due to the chain being offset from the center-plane of the frame. It's not threoretical; you can feel it underfoot, and even see it by eye: the lower run of the chain sags visibly when cap'n applies force to the pedal, enough sometimes to cause the chain to derail, which can cause a crash. That type of flex is the main reason why some bottom tubes are oval instead of round.
Even if it didn't flex the frame, having double the chain tension can result in the chain snapping. I've seen it, happened right in front of me when Nelson Vails and Scott Berryman were on a Team USA sprint tandem. When they jumped, the timing chain broke. That's the captain's pedal force only BTW, stoker's strength doesn't go through the timing chain at all. So Vails broke that chain all by himself. And it wasn't a tiny chainring, it was Campy 144 BCD, so we know it was at least a 41t, probably bigger. Him on a chainring half as big would have sent shrapnel into the bleachers!