R pope beat me to it. add more castor. with the castor angle ( forward or rearward tilt of the suspension components ) if it's too far negative ( or less positive ) then every bump in the road you will feel, because the vehicle weight does nothing to center the steering wheel, with more positive castor, the wheels turn out up and down wise more, but the weight of the vehicle holds the steering str8, also because of this, castor provides automatic return to center ( this is why go carts, lawn mower ect.. will not, but 4 wheelers and such with adjustable castor will ).