After all is said and done, my best guess is its Belt Chatter Vibration. I have Tried all the tricks, and read all the threads and after getting front wheels spun balanced at a Tire shop, plus Lazar alignment on my new 2016 RT Limited, and having my Dealer adjust the Belt tension to try and remove the vibration, all it did was move it from 60 MPH to 70 MPH. So my next move was to buy Doc's Vibration Dampener for my RT. After installation, I reported here on another thread that I really could not tell any difference after installing the Dampener. I than bought a Tension Gauge and checked belt tension, which was to Factory Specs. The Vibration stayed. Then, I discovered the spring on Doc's dampener was broken. Doc said he would waurentee a new Spring that should have been on my RT but was made for the F3. So I got the new Spring, installed it again, and after installation, the vibration "appeared" or "felt" like it had decreased. But it quickly reappeared again, and I still have it from 60 MPH thru 75, then it smooths out. My present conclusion regarding the Belt Dampner is,...regardless of the Manufacture, its a good Placebo. I now have 7500 miles on my RT, and have not changed my OEM Kenda tires. The rear is obviously quite worn, whch I plan to change around 10,000 miles if possible to a new Khumo I have sittng in my garage. I had a 2012 RT with 55,400 miles on it when I traded it, and I had used 3 Khumos on it, getting about 15,000 miles on them, so I like that tire. My front Kendas seem to be wearing evenly, and have lots of life left in them, but all 3 tires are obviously not balanced the same as when new, so surely is contrbuting to my increased vibration which no Dampener is going to completely eliminate. My Dealer told me that the Belt also stretches with wear, so needs to be readjusted periodically, so that's another contributing factor to the vibration. I keep checking my new Tensioner spring, and after 1500 miles, it has not broken again, and the Roller is not loose or wobbly, so its doing its Job of being a good Placebo, and as long as I ignore the vibration, ......it is not there below 60 and above 75. In my opinion, the only cure for the belt vibration will be a Drive Shaft, or some Engineering to greatly reduce the length of the belt drive. Well, the sun is shinning, and it isn't raining, so I am going for my daily 100 mile cruise and fully anticipate the usual vibration which is, has been, and most likely, will continue to be the Nature of the Beast, in spite of the complaints, hype of good and bad reports, and Prayers for BRP to step up the plate and recall every Spyder with Belt Vibrarions, and install a a waurenteed Up Graded Drive Shaft conversion to replace the Belt Drive. I won't hold my breath waiting, tho!
How many miles on the bike. I tend to agree with Joe. Loose ball joints or bushings could cause the problem.
