I know about adding mass. When I ride citibike and strap my laptop bag to the front basket, the handling becomes so heavy and when I ride with no hands (on the 10% of bikes that actually tracks straight), I have to really shift my body weight around just to make corrections and keep the bike straight. I did do a quick ride with the front fork/handlebar rotated 180 deg, creating a negative trail and vastly increasing the trail (it must have gone from 28mm to over 75mm). This made the bike ultra stable, thought about using this setup for my wife, but then I didn't want to use the bike not as it was intended.