Yesterday I took my C past 80 for the first time. It had been over 800 miles and just hadn't done it. As soon as it hits 80 though, there is a lot of vibration. My last C was like this until past 100. I have no idea why it vibrates so much, the only solution I can think of is all the electronics I have put under the seat, which fills the gap between the seat and frame, and now transfers the vibration. I don't know...