When I got my new 2016 FXS I could feel right away that the belt was way too tight. I bought one of those Krikit gauges but I got a wildly different reading every time I used it, so I then bought a proper gauge...
https://www.amazon.com/OTC-6673-Universal-Tension-Gauge/dp/B000I198J0This revealed that the belt was set to around 100lbs (from the factory!). I adjusted it back to factory spec and it felt much better. No creaking, groaning and general squealing. After doing a bit of experimenting, I decided that the Krikit is OK for getting a ±50% type of reading if you need something for an emergency set up by the side of the road, but its no substitute for a real gauge.