I know things... A lot of things.
Join Date: Feb 2015
Motorcycle: GSXR 750 K4
Re: New springs?
Coil springs can be progressive, either by changing the diameter, or the pitch along the length of the spring, either continuously, or discretely, that is, in steps. I see no such features, at least not on any significant scale, on the OEM springs. The suspension itself, is nonlinear, due to its design, but you can't change that, at least not by changing springs.
I'd advise against changing springs, unless you have specific issues with the existing setup. That way, at the very least you have a certain idea of what to expect from the new parts. If all you expect is "a better suspension", then I would predict two possible outcomes: either you'll discover things don't work that way, which is, in my mind, the good alternative, or you'll be happy but misled, attributing to the new springs, changes to the bike's handling, which might well have nothing to do with them. (Instead, they might, for instance, be the result of attendant geometry changes which could have been achieved with the old springs just as well.)