I'm pretty sure this has been covered. Anyway, I just accidentally discovered a simple but darn effective way to align the handlebars to the front tire. I guess most of us try to align the bars by eyeballing it while keeping the stem straight relative to the top tube. The problem with this method is that the rear half of the front tire can't be seen because its view is blocked by top/bottom tubes making it difficult to see the angles between the bars and tire. Now, turn the stem to either side. Doesn't matter how much. Now you can have an unobstructed view of the whole front tire, telling you right away if the alignment is correct or incorrect.