Code Of Federal Regulations; Title 49, Transportation: Part 569

1. The tire must be regroovable (the word "regroovable" must be labeled on both sidewalls).
2. The cord material must be protected by at least 3/32 inch (2.4 mm) of rubber after regrooving.
3. After regrooving, the grooves shall have at least 90 inches (228.6 cm) of edges per linear foot (30.5 cm) of tire circumference (count the edges on both sides of a groove).
4. Regroove width must be 3/16 inch (4.8 mm) minimum and 5/16 inch (7.9 mm) maximum.
5. Regrooving must provide unobstructed fluid passages (either to the side or fore and aft).
6. After regrooving, tire inspection must disclose no:
   1. Cracking extending to the cord material
   2. Groove cracks or wear extending to cord material
   3. Ply, tread, or sidewall separation

Sipes or microsiping is allowed, but it must not damage the cord or be deeper than the original or retread groove depth.