I expereinced some roll PIO in some earlier days on my Air Command - with heavier Skywheels blades. I discovered that the stick would shake a lot less if I tightened the roll and pitch pivot bolts for more and more friction. At some higher friction point, the "sticktion" must have added some delay in my roll response and I unexpectedly PIO'd in roll. Stopped it by not moving the stick. Landed immediately and loosened those bolts a bit!
Another way to experience (or think about) PIO (and buntover) in a car is to drive in reverse fast - faster than you are proficient at. In reverse, the steering is statically unstable which means it tends to stray further from straight quickly - "buntover"! (try not to roll over!) And, if the "pilot" is able to stop the "buntover" with quick reversal steering commands, it is likely that he/she will start to PIO back and forth. Things get worse the faster you go - which may also analageous to flying a statically unstable gyro at higher airspeeds. In this auto case, there is little dynamic damping, but it would be instructive to discover if it is easier to PIO in a heavier car or a lighter one - inertia to overcome is higher or lower, but dynamic damping is nil. (Inertia and damping are components of the inherent dynamic response. But, without inherent damping, the "pilot" is the dynamic damper - just as in a statically unstable gyro without little dynamic damping.) The quickness of steering is also a factor - as it is in gyro cyclic quickness.
Thanks, Greg Gremminger