This is sortof a mix of physics, engineering and metallurgy so I'm not sure if this is the best place for this, but I figured it will get sorted out. I am looking into adding an after market rear-suspension device to my recumbent bike which attaches at the rear dropout and what would be the seat stays on a normal diamond frame bike with cromoly stays. This mod has been done on other 'bents but the seat support stays on those are also cromoly. My particular bent has aluminum stays that are adjustable by a tube-within-tube design held in place by a pin. The forces created by the suspension device should be linear to the support stays, thus putting most of the force on the pin as well as where the stays attach to the frame and seat. Is aluminum going to be significantly weaker than cromoly for this application or does it have comparable tolerances for such linear forces? If this is too complicated to visualize without some pics I can post some if desired.