I have seen quiet a few road bike with a Z-shape seat stay until now, e.g. specialized Roubaix
Does it serve any purpose? What's the advantage of this design in comparison to a straight-bar seat stay?
They add a bit of suspension to the bike
HOW IT’S DONE From It’s CG-R seatpost to the Zertz viscoelastic dampers in the fork and seatstays, the Roubaix is designed to filter both high frequency vibrations and big hits from the road— so your body doesn’t have to.
ZERTZ The Zertz vibration dampers are designed to take the edge off of high the frequency imperfections that every road rider rider knows well. From chip sealed roads, to cracks and everything in between, Zertz take the edge off of even the worst road surface.