Font set spaces size

Hi, I'm using the method setSpacesSize http://openframeworks.cc/documentation/graphics/ofTrueTypeFont.html to change the dimension of the space between the words. It looks like it has no effect, I've tried with different fonts but I've always the same result. Am I doing something wrong?

ofTrueTypeFont font;
font.loadFont("OpenSans-Regular.ttf", 30);
font.setSpaceSize(3.0);