You are looking for the attribute 'offsetR' which works like padding. The is located inside the 'scaleR' object, which is the scale used for radial charts. From there to adjust the numerical values, you must modify the 'item' object.
scaleR:{
item:{
offsetR:45
}
}All documentation referenced here:
http://www.zingchart.com/docs/json-attributes-syntax/graph-objects/scale-r/