This is somewhat generic but does apply to the spyders as well.
I just finished replacing the engine output bearing on a 2006 Kaw Vulcan that I am converting to an RT. The belt was tightened to the key of G and consequently the bearing took a dump.
Normally replacement requires total removal and disassembly of the engine however I have a machine shop so the replace and repair only took an hour and did not require any real disassembly.
I have talked to several Spyder owners who are experiencing vibrations at higher speeds which I am linking to overly tight drive belts which are harmonically tuned to higher rpm. My advice to all is to loosen that belt. These Grimler belts are not designed to run tight and do not stretch like a chain will so engine and wheel hub damage will result if they are run tight.
One of the issues is the swing arm and shaft center are alined to the rear axle on differing arcs so if the belt is over tightened when the bike is unloaded the belt will normally get even tighter when the suspension is compressed causing some real concerns on my part.
There is no too loose setting as no damage will occur to the belt or pulleys by an over loose condition however the belt may rub on guards or engine case so there is a limit.
I know most shop mechanics do a pretty good job of overtightening and to be fair there is some consolation in the term "good and tight"
So just friendly advice - give loose a try and see if things improve. I know every time I work on any bike with a drive belt the very first thing I do is loosen that belt and so far 100% have been way over tight.