Cannondaleriders

I'm setting my E440 up for my son for a dual sport ride we are doing and need to figure out the spring rate to get close (I'll check/set sag to get it perfect).
My son is ~160 lbs and I have springs ranging from 31/95 up to 36/105. I'm figuring start with the light one. We'll be riding in the rocks in the Sierras so want
to stay on the softer side. With Cannondaler gone I can't really look anything up for bike suspension. I have the forks covered already since I have a large range
of fork springs to select from.

Thanks

It's been a while for me. But I seem to remember , if you install the spring and have to preload more than a certain measurement to get proper sag. You need a heavier spring.