I used a lowered Works shock that lowered it an inch and 1/4, then switched to a 60 series tire. Works is out of business, and I don't know if their successor, Worx, sells a lower shock for the ST1100. A similar rear shock is sold by Wilbers. This shock lowers 30 mm or 1.18 inches. All told, I lowered the rear an inch and 3/4.
shock absorber Type 640 Road - The basic edition of the Wilbers Adjustline mono shock absorber comes along with the same technology as the more complex versions. The difference is that here we leave o
www.wilbers-shop.de
I took the bike to a suspension shop to lower the front. Remember that shortening the forks an inch only lowers it .8 or so due to the angle of the forks. The forks can be pushed up in the triple trees 3/4 inch, which gives you a little over a 1/2 inch lowering. I think he shortened the spacer that brought it the rest of the way. He fine tuned the height with the fork, because it was only up in the triple trees 1/4 inch. I kept the stock springs and changed the fork oil and seals.
It made a huge difference for me.
You will have to shorten the kickstand and center stand.