What controls or can be modified to increase the turning radius of a car?
First...If you increase your turning radius, you will make a bigger circle as you turn.
I think you want to Decrease you turning radius.
Second there is lots of things you can do to "decrease"
your turning radius. They all have to do with geometry of your Steering componets and how they work with each other component. The wheel base length is critical, as well as the Ackerman angle of the front end.
The car turns or rotates about a point that is located along an imaginary line that is roughly equadistant between the rear axle center line and the front spindles. near the midline of the car. i I guess the place to start would be understanding the dynamics of a turning car.When an automobile is negotiating a corner, the vector sum of the forces acting in the plane of the tires' contact patches points toward the instantaneous center of the turn. The tangent to the automobile's path is perpendicular to the radius defined by this center and the vehicle's center of gravity. The contact patch is the portion of rubber at the bottom of the tire which lies against the pavement. For a perfectly elastic tire, the product of this area and the tire's gauge pressure would equal the load supported by that tire. The force of adhesion developed in the contact patch may be found by integrating the rubber stress against the contact area. The size and shape of each contact patch changes during cornering, being a function of the centripetal acceleration and the normal load .
The stress that may be reacted by each element in the contact patch is a function of the elastic properties of rubber,the ultimate stress being achieved when the rubber shears. This stress arises through molecular attraction of rubber for the road, and the mechanical interlocking of rubber with pavement irregularities.
One interesting aspect of this force development is the fact that the line of intersection of the wheel plane with the road will point in a direction different from that of the tangent to the turn radius. The angle between these two directions is called the "slip" angle, but do not take the word "slip" too literally.
I would just lenghten the pitman and idler arm lenghts about an inch. and make sure the front wheels don't rub.
Shortening the wheel base would drop the radius and therefore increase the speed of the turn about its roll center also. I guess in the end it just your call.