My Roubaix SL4 came with 25's. I actually went from 23's to 28's on my Trek. Do you think going to 28's on the Roubaix will be an issue? I just like the wider tires and more contact patch. I have a brand new set of Gatorskin 28's here I got for the Trek and never installed.
I don't think clearance will be an issue.