Yes, the Tiger arrived with 13". Not certain but about 5.5" wide. Did I mention inadequate?
My GT2 used to run on 8X13 rims shod with Goodyear Bluestreaks, about 9.5" wide. Definitely mo stukum mo adequate.
SCCA now allows 15 or 16's and 8 or 9 wide. Assuming one can fit them, that will certainly help glue the ponies to the ground.