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. Inside 'scaleR' adjust the numerical values by adding the attribute within the 'item' object.
scaleR:{
item:{
offsetR:45
}
}All documentation referenced here:
http://www.zingchart.com/docs/json-attributes-syntax/graph-objects/scale-r/