Dynamic tick font siziing - based on http://jsfiddle.net/900k/ej4ujx81/4/

c3.js

@@ -6977,7 +6977,7 @@
         }
         function textFormatted(v) {
             var formatted = tickFormat ? tickFormat(v) : v;
-            return typeof formatted !== 'undefined' ? formatted : '';
+            return typeof formatted !== 'undefined' ? formatted.toString() : '';
         }
         function getSizeFor1Char(tick) {
             if (tickTextCharSize) {
@@ -7079,7 +7079,7 @@
                     var dy = sizeFor1Char.h;
                     if (i === 0) {
                         if (orient === 'left' || orient === 'right') {
-                            dy = -((counts[d.index] - 1) * (sizeFor1Char.h / 2) - 3);
+                            dy = -((counts[d.index] - 1) * (sizeFor1Char.h / 2) - sizeFor1Char.h / 4);
                         } else {
                             dy = ".71em";
                         }