Chris, I suspect you may be thinking about Solo 2. AFAIK, there is no "approval" required for tires in the ITCS except that they be DOT-approved.
Thumbing through my 2004 GCR, page ITCS 17, par 7.a.2, "Any DOT-approved tire is permitted." There are no further restrictions to, or requirements for, tires in Improved Touring...
GregA