Turtle?.....
Anyway,... common method is tighten 'till you can twist it 90" degrees at mid-point...
Very dependent on thumb strength... I can turn it to 90, at any adjustment... and I've seen your picture,... you can turn it 180'...
Tighten it, to where there's no flop, but it can be moved up and down 1/2" to 1" without making a grunty noise...
Harley goes way tighter than that... but as long as it's not able to slip a cog, it's fine...
I have 12" shocks, so I like a bit of leeway for travel...
Changing is easy,... pull the back wheel and the front cover plate.. that's it... wait,.. might have to pull the left shock... no biggy, two bolts there...
I've never had to replace one...
My bike has 22k miles and the belt has no wear... other than, when I took an angle grinder to it, to make it shut up...
It's quiet now....
BP beat me to the post,.... not that I'm knockin' the 90' method... it just doesn't work for me...
a turtle, huh?.... That's cool...