I can recommend the book by Paul Thede and Lee Parks (with illustrations by my friend Alan Lapp)
https://racetech.com/suspension-bible/and also the book and software by Tony Foale:
https://motochassis.com/as noted here:
https://www.reddit.com/r/motorcycles/comments/obpe7f/does_preload_make_a_spri...it might be better to say that cranking up the preload doesn't make the spring "firmer" (stiffer) but it will increase "harshness" by increasing the amount of force needed to get the suspension to start moving. Changing preload can possibly compensate to a degree for an incorrect spring rate, but it doesn't change the spring rate.
On the CTX 700 Hondas people add washers to increase the preload on the OEM rear spring because the spring rate is often too light and the suspension is almost bottomed out when the rider (and maybe passenger and luggage) are added. The extra preload helps to extend the damper (raising the ride height) so some movement in the damper rod is available, but the spring is still too light and will bottom out easier than with the correct spring rate.
Suzuki says the rear wheel travel on the Savage is 80mm. With such a short travel they'll have to run a stiff spring and possibly crank up the preload as well so the suspension isn't practically sacked out all the time. But that's the price you pay for a bike where a very low seat height is a major design concern unless you are able to jigger things around to get both decent suspension movement and the low height at the seat.