Steve Kurt wrote:
"The curved seat tube was unique to Schwinn (at least to my limited knowledge), and I don't recall it being used on the low-end tandem models. Was the purpose of the curved tube just to keep the frame tubes short, and thereby reduce the flex that was typical of tandems of that era?"
Curved seat tubes were actually quite common in short wheel base tandems
in Britain. You can see a couple photos of my late 70's Bob Jackson
here:
http://www.wooljersey.com/
This big difference between the Schwinn and these British short wheelbase tandems is that on the SWB tandems the wheelbases were actually shortened by the use of the curved seat tube. On all the Schwinns that I have seen, you could just as well have inserted a straight seat-tube without it affecting the wheelbase. To understand this look at the tight clearances between rear seat tube and rear wheel on my tandem and compare to those on the curved tube Schwinn tandems.
As far as the flex of these old tandems, I have never found them to be overly bothersome. Indeed I prefer riding my old 'flexy' Bob Jackson to the newer 'stiff' tandems.
Steven Maasland
Moorestown, NJ
USA