I don't have a c90 but my brother-in-law does and we ride together all the time. We put some 3" Hard Chromes on his bike and they sound wonderful....(his bike sounds better than mine and I am just de-baffled). He bought a power commander along with the pipes but we never put the power commander on cause he wanted to see how it rode without it. Rides fine and I don't think he is going to install the power commander any time soon. Hope this helps, and good luck on your decision.