I noticed this problem, too, recently. I've got a Cateye wireless (a little more than a year old), and after descending a long hill the other day, I wanted to check to see what my max speed had been. Usually, I hit around 40-43mph coming down this particular hill. But when I checked it this time, it said 77mph! I've never had any problems with this cyclometer, I didn't have a cell phone with me, etc. Weird.