I tried everything I could think of to make the tongue with the split steel rims work. I bolted them in 4 or 5 places, put in a second connecting point to the main frame, and then took the brackets from a bolt on kick stand, and clamped it around the tongue and cross brace. It still had too much flex and when Jim grasped it at the cross brace and the end of the tongue he was able to easily bend the tongue upward.
I will try using wider, stiffer alloy rims, at Stewart’s suggestion. I like the shape, it has lots of clearance for the wheel of the bike during turns, and it would be light weight. But if its not strong enough to handle the loads, then it just won’t work.
We are also going to try something that Jim had suggested, and Kevin brought up again, which is using the down tube and seat tube from a step through frame. This will be a lot stiffer, a little heavier, but may end up answering some other design needs. The problem it may present is, will there be enough clearance for the rear wheel when turning in a tight circle? There are a lot of step through frame styles and some will no doubt work better then others.
Fortunately, there are a lot of under appreciated step through frames out there. A lot of folks would call this frame design a “girls” bike and don’t want one. The truth of the matter is a step through frame has a lot of advantages over a diamond frame, Easier to get on and off, no top tube to fall on to, and a kind of built in suspension.
The process continues, some things will work, some won’t, the trick is to have the patience to work it through and to try everything you can come up with to solve the problems as they present themselves. If it doesn’t work, don’t throw away your notes, you might come across some idea that makes it work. If you take the time to review what you’ve done in the past, that didn’t work, you won’t have to go through the process again.