Handling Stability Parameters I'm building my first bike: probably steel (easy to work with). 2X26" road tires. Full suspension. Will be used on sandy dirt roads, and paved streets with moderate incline. Want hands free option, and good directional stability--both seated and standing on uphill sections.

Which design factors will help stability? How much trail, fork shape, crank more forward or backward? What else?
I'm just going to make a list of all the factors I can think of that affect stability, but please be aware that this list is not exhaustive.


front tyre size/width
front tyre weight
front tyre pressure
front wheel size
front wheel rigidity
headset angle
trail
front fork rigidity
front fork travel
front fork suspension friction
front suspension travel shape
front fork preload
stem length / handgrip position relative to steering pivot 
handlebar rigity
grip size and firmness
primary frame/main triangle rigidity
main triangle size and angles (affects BB to handlebar and seat position)
rear triangle rigidity
rear suspension type
rear suspension travel
rear suspension travel shape
rear suspension preload
slop in suspension pivots (all six axes)
slip in all the other bearings - headset, bottom bracket, wheel axles etc
BB to ground distance
seat height
seat front-back position
seat firmness
Q factor (BB/crank/pedal spacing)
chainstay length
rear wheel size
rear wheel rigidity
rear tyre size/width
rear tyre weight
rear tyre pressure


I am certain that I have missed some, and a few of the entries above should really be split out a great deal more - the rear triangle could be made of composite materials allowing fine, semi-independent control over rigidity in different axes, for example. And vertical compliance of the main triangle is a subject of intense discussion in some cycling circles. Likewise, suspension design is a complex subject that's quite different from suspension tuning, but I've largely conflated them in the list above.