John and Cecil wrote: ↑Jun 23 2018 7:08pm
Something like this maybe?
rack.JPG
The closer the connection points are to each other, the better the triangulation and the less stress on every part.
It should be possible to flip the new diagonal slides over and file or cut (hacksaw) or grind away just enough of the "L" rail on each side of the main flat area at the mounting end point to allow it to fit under the existing rails and up against the dropout/frame.
Without the L portion all the way to the end it won't be as stiff at that end but since it's just triangulation tying two points together, it makes less difference than it would to the other (vertical and "horizontal") struts.
If it could be welded along the mating edges it'd be better, but bolting the flat part is good enough for this.
Regarding the mirror, if you have a celphone, you could temporarily mount it to the back fo the seat and leave it recording video while you ride, then watch it later to see how he behaves thru all of it. Since the phone is on hte seat and he's on the suspension, you 'll be able to see when you hit bumps cuz he'll move up in the vid, and when you hit holes he'll move down.