I was messing around with the '85 Ironman that I just picked up the other day and thought I'd take a pic of the tire clearance. I've heard from several people that the '85 had more clearance than the later years.
It currently has 25mm Continentals on it, and does look to have plenty of room to move up!! Please excuse the dirt and grime... I still have yet to tear it down for a good cleaning