The front guard that goes on the down tube has a groove for a round shaped tube, but the nature of securing it to the frame should give you no problems, providing that the down tube isn't too wide. The guard is secured to the bike with two very strong rubber bands. You may need to give them a little stretch if the down tube doesn't slot nicely into the groove. If your down tube is too wide and is more like a square shape it may not fit in that groove at all, and those bands are quite tight. See the attatched photos.