I have a Nitron R1 rear shock on my 23’ Svart. It has a spring set for my weight of 90-95kg the spring is 800lb or 140Nm. I also have fitted YSS fork springs at 7.5Nm, they are for the KTM 390 Adventure but fit perfectly in WP forks. I changed to Motul 5w fork oil.
The handling has dramatically improved over the stock suspension. Even with a lot of fiddling and testing the standard shock could not provide the feel I wanted. Like the forks the progressive spring is too soft in the lowest rate and too stiff in the highest rate. The damping is far too much for the spring even at its max preload setting and minimum rebound. I believe both the spring and the damping are at fault, for my weight and riding style anyway.
The standard forks have the adjustment but the progressive spring is way too soft in its lowest rate and way too hard in its highest, meaning you can only get good damping in the middle of the stroke but the spring compresses too much to use the soft part of the spring and the hard part just feels like you have bottomed out. I you wind in Compression to stop the fork dive you lose the suppleness, the springs in the front are at fault.
There are cartridges available but I felt the springs sorted the front for me.
I can now throw the bike into corners with so much confidence and know the (Standard Rally STR) will keep me gripped. I have thought about fitting sticky road tyres but really have no need now the suspension is sorted.
Hope some of this rambling helps, Jes.