Keep in mind that though this is true, it isn't from the crank arms or BB, it is the better chainrings that come with it that makes for smoother/shifting, which if you wanted to, you could simply purcahse new rings. But, If I had tiagra, I wouldn't waste my money to try and make a bottom shelf crank feel like it was mid class. If you are going to put any money into an upgrade, make it worth while. If I were looking to upgrade from tiagra, I would go sram rival, fsa slk or ultegra AND then purchase praxis works chainrings.