Resolved #305; Now you may pass axis.y.tick.rotate

c3.js

@@ -1098,7 +1098,8 @@
             axis_y_label: {},
             axis_y_tick_format: undefined,
             axis_y_tick_outer: true,
-            axis_y_tick_values: null,
+            axis_y_tick_values: null,        
+            axis_y_tick_rotate: 0,
             axis_y_tick_count: undefined,
             axis_y_tick_time_value: undefined,
             axis_y_tick_time_interval: undefined,
@@ -4339,9 +4340,14 @@
     c3_chart_internal_fn.yForRotatedTickText = function (r) {
         return 11.5 - 2.5 * (r / 15) * (r > 0 ? 1 : -1);
     };
-    c3_chart_internal_fn.rotateTickText = function (axis, transition, rotate) {
-        axis.selectAll('.tick text')
-            .style("text-anchor", rotate > 0 ? "start" : "end");
+    c3_chart_internal_fn.rotateTickText = function (axis, transition, rotate) {    
+        if (axis.classed(c3_chart_internal_fn.CLASS.axisY) && !this.config.axis_rotated) {
+            axis.selectAll('.tick text')
+                .style("text-anchor", rotate > 0 ? "end" : "start");
+        } else {
+            axis.selectAll('.tick text')
+                .style("text-anchor", rotate > 0 ? "start" : "end");
+        }
         transition.selectAll('.tick text')
             .attr("y", this.yForRotatedTickText(rotate))
             .attr("transform", "rotate(" + rotate + ")")
@@ -4473,6 +4479,10 @@
             $$.rotateTickText($$.axes.x, transitions.axisX, config.axis_x_tick_rotate);
             $$.rotateTickText($$.axes.subx, transitions.axisSubX, config.axis_x_tick_rotate);
         }
+        // we may want to rotate y axis when chart in horizontal
+        if (config.axis_y_tick_rotate) {
+            $$.rotateTickText($$.axes.y, transitions.axisY, config.axis_y_tick_rotate);
+        }
     };
 
     c3_chart_internal_fn.getClipPath = function (id) {

spec/axis-spec.js

@@ -569,6 +569,49 @@ describe('c3 chart axis', function () {
         });
     });
 
+
+    describe('axis.y.tick.rotate', function () {
+
+        describe('not rotated', function () {
+
+            it('should update args successfully', function () {
+                args = {
+                    data: {
+                        columns: [
+                            ['data1', 30, 200, 100, 400, 150, 250, 100, 600],
+                            ['data2', 50, 20, 10, 40, 15, 25],
+                        ]
+                    },
+                    axis: {
+                        y: {
+                            tick: {
+                                rotate: 45
+                            }
+                        }
+                    }
+                };
+                expect(true).toBeTruthy();
+            });
+
+            it('should rotate tick texts', function () {
+                chart.internal.main.selectAll('.c3-axis-y g.tick').each(function () {
+                    var tick = d3.select(this),
+                        text = tick.select('text'),
+                        tspan = text.select('tspan');
+                    expect(text.attr('transform')).toBe('rotate(45)');
+                    expect(text.attr('y')).toBe('4');
+                    expect(tspan.attr('dx')).toBe('5.65685424949238');
+                });
+            });
+
+            it('should have automatically calculated y axis width', function () {
+                var box = chart.internal.main.select('.c3-axis-y').node().getBoundingClientRect();
+                expect(box.width).toBeLessThan(25);
+            });
+
+        });
+    });
+
     describe('axis.x.tick.fit', function () {
 
         describe('axis.x.tick.fit = true', function () {

src/axis.js

@@ -260,9 +260,14 @@ c3_chart_internal_fn.xForRotatedTickText = function (r) {
 c3_chart_internal_fn.yForRotatedTickText = function (r) {
     return 11.5 - 2.5 * (r / 15) * (r > 0 ? 1 : -1);
 };
-c3_chart_internal_fn.rotateTickText = function (axis, transition, rotate) {
-    axis.selectAll('.tick text')
-        .style("text-anchor", rotate > 0 ? "start" : "end");
+c3_chart_internal_fn.rotateTickText = function (axis, transition, rotate) {    
+    if (axis.classed(c3_chart_internal_fn.CLASS.axisY) && !this.config.axis_rotated) {
+        axis.selectAll('.tick text')
+            .style("text-anchor", rotate > 0 ? "end" : "start");
+    } else {
+        axis.selectAll('.tick text')
+            .style("text-anchor", rotate > 0 ? "start" : "end");
+    }
     transition.selectAll('.tick text')
         .attr("y", this.yForRotatedTickText(rotate))
         .attr("transform", "rotate(" + rotate + ")")
@@ -394,4 +399,8 @@ c3_chart_internal_fn.redrawAxis = function (transitions, isHidden) {
         $$.rotateTickText($$.axes.x, transitions.axisX, config.axis_x_tick_rotate);
         $$.rotateTickText($$.axes.subx, transitions.axisSubX, config.axis_x_tick_rotate);
     }
+    // we may want to rotate y axis when chart in horizontal
+    if (config.axis_y_tick_rotate) {
+        $$.rotateTickText($$.axes.y, transitions.axisY, config.axis_y_tick_rotate);
+    }
 };

src/config.js

@@ -111,7 +111,8 @@ c3_chart_internal_fn.getDefaultConfig = function () {
         axis_y_label: {},
         axis_y_tick_format: undefined,
         axis_y_tick_outer: true,
-        axis_y_tick_values: null,
+        axis_y_tick_values: null,        
+        axis_y_tick_rotate: 0,
         axis_y_tick_count: undefined,
         axis_y_tick_time_value: undefined,
         axis_y_tick_time_interval: undefined,