Originally Posted by Steve Katzman
I am no expert on what steel tubing is generally used by tandem builders today. I don't even know exactly what tubing is used on my 2003 Co-Motion Speedster, except the Co-Mo calls it air-hardening and it is definitely oversized diameter. I believe that Santana steel frames are similarly oversized. Based on this, I would conclude that the differences in stiffness between aluminum and steel are much smaller than those reported in Rinard's tests.
Santana & Co-Motion have been using oversized steel tubing for many years, noting that even our '96 Arriva had Santana's "Megasize" 8/5/8 tubing and, with the exception of the newer ZR9000 and a few scandium tandems built by Erickson & Bushnell, there haven't been too many tandem frame material changes in the steel and aluminum camps as carbon has been the focus of most builders, forks or frames. But, be that as it may, what you suggest could very well be the case. So, rather than guessing and relying on old data I'll see if I can get an answer as to whether or not the deflection gap has been narrowed and let you know.