I also ride two- up and loaded a lot. I do not find that the load on the bike is all that important to the front suspension set up though, it is very much more important to set up the rear suspension; most of the added load on a motorcycle is very well toward the rear.
That spring sounds just about right to me, as I said, I would go 1/2 way between the stock ZX and C-14 springs, and 1.05 is just about perfect I think. Another thing you can do is drop the viscosity of the fork oil and then adjust both the compression and rebound damping given ZX 14 forks; I think that would be a much better setup than the factory C-14 forks.
I bottomed out the front end once or twice before dialing up the compression damping, which worked very well for me. The spring pre- load is set to the max., and the ride quality is MUCH better than the stock forks, which I find too stiff both in spring rate as well as damping.
Brian
P.S. I want FULL CREDIT for not putting in one single smarta$$ answer regarding 'how I ride my bike' (mostly forward, tires down, etc., etc.) as well as not putting a single 'Easy Boys' anywhere after mentioning the stiffness of the damping.
BDF how do you use your bike? I use mine a lot two up and also two up loaded. How have the zx14 springs handled the xtra load when two up?
I see the springs are .95kg (zx) vs 1.2 kg (std)
I was talking to a suspension guru and said he would "never put in anything more than a 1.05kg in forks". 0.95kg from the zx might be very close to the mark. Maybe a 1.05kg (approx) might be good for two up?