Car tires on 1992 Honda ST1100

I have a 1992 Honda ST1100 with a 2005 Hannigan Conte Classic side car. The tires that are on the ST are (F) 110/80-18 and (R) 160/70-17. I would like to ascertain if there are car tires out there that will fit the existing wheels. Just as a side note, when I purchased the rig, the previous owner had installed a different size tire on the sidecar. When I noticed that the tire had rubbed into the fiberglass wheel well near the front of the well, I contacted Hannigan and that is when I learned that the wrong size tire was on the sidecar. I have corrected that and there is no problem in that area. I am just trying to find out now about the chances of changing the tires on the MC without running into unknown problems. Any thoughts would be appreciated. Al Irwin 909-631-6063