I ran Sonic Springs on my VFR and the springs I bought from them and put in my VFR800 were way too stiff.
I used the ones they recommended on their chart according to my weight and riding style but they make the stock BBXX springs feel downright plush.
I will say their customer service was terrific.
I would like to hear from those of you running them on a BlackBird and get your impressions?
Your weight, riding style, spring weight, and oil viscosity.
Thanks