I've tried a lot of different tires on this bike. Here are a few of them . . .
BFG Mud Terrain, 215/75-R15:
Michelin M4 Rally, 16/65-15 ZEL90 (with a small modification for sand dunes):
Greenway Aligator, 15" (rear), Michelin M4 Rally 13" (side):
Silverstone Rally, 15":
A few spares:
Hoosier mini sprint car tires, 10":