maybe angle of the frame (trying to make a place for the leaf to sit flat)
Torque flex (when you load up the front trying to climb up something, and the springs stretch out and you fall over backwards?)
I've seen a missing link (double shackle) setup on the front before. JimJob from Polock Pines used to use that setup on his front with 150 springs.
Con.....I already max out my 9012's easily.