There's a whole lot of things that might cause you to feel a vibration somewhere in the bike, even things occurring as far away from the floorboards as you can get, but to be truly helpful we really need a bit more of an in-depth description of the vibration you are feeling??

Does it only occur at a given road speed or in a given range of road speeds; or is it there all the time regardless of speed? What about when accelerating or decelerating - does it vary any then? Is it only in a given gear, or all gears? Or is it only at a given rev range regardless of gear selection? What about if you're just coasting, is it still there then? Does it only happen on one particular section of road; type of road surface; or is it there on any/all road surfaces? Have you tried changing the belt tension (not adjusting the belt vibration damper, which
ISN'T actually a belt tensioner anyway, despite that being what you erroneously called it!

) What about adding a dab of appropriate belt grease to the belt itself - does that make any difference?? And have you had a proper wheel alignment done yet? Altho that lot's really just for starters! :shocked:
However, I guess you're still running the OEM Spec Tires?? :dontknow: If so, you might want to try another set of tires & rims (preferably not Kendas/OEM

) - you might hafta beg, borrow, buy or rent another set off a friends Spyder or the dealer's stock to see if that makes any difference; fronts only if that's all you can manage first up; but if you've looked at everything else & that still doesn't sort it, try swapping the rear too. :thumbup:
So it could be any one of or any combination of things in that lot, and I'm sure there's a bunch more besides.... :helpsmilie: But if you check thru all of those and you've
STILL got an annoying vibration that you can't get rid of, you might be surprised at the number of people who've spent a
LOT of time &/or money unsuccessfully chasing a vibration thru every other part of their Spyder/Ryker, only to finally bite the bullet & eventually/begrudgingly swap the OEM tires over to a set of a/mkt tires &/or sometimes swapping out the rims too
and only then do they discover that their un-traceable vibration has
finally gone.... :shocked: The bad news is that for some, it can be the rims too, rather than just the tires; and sure, the rims/tires being the source of these sorta vibrations is occurring waaayy less often now than it once did, but it's still happening often enough to be of concern.... :banghead:
Just Sayin'

Good Luck! :cheers: