The Marzocchi shiver springs come in 2 different stiffnesses. .45 or .5.
The forks I bought used already had the stiffer springs.
I am NOT a fan of progressive springs. Prefer straight rate.
BMW stock spring rate available here:
Says .44 which is why I wanted the stiffer springs.
BTW I don't think racetech's spring rate calculator for the BMW F800 is correct. It says at 185 lbs I should have 0.876 kg/mm spring. That would in my opinion be way too stiff. If you go to the G450X and check there for dirt riding at 185 lbs it says .48 spring. If you add some for the weight of the bike then .05-.55 is probably closer. That was my figuring anyway. The Marzocchi Shiver'd conversion I did siffened it up nicely and tuneability is great.