From: Sgt. Jacalyn Sticha
Minnesota State Patrol
Q. Is the correct depth for my tire’s tread depth really to the top of Abe Lincoln head on a penny?
A. Close, I actually got a penny out and measured. However, the law states, “ … the depth must not be less than 1/16 of an inch measured in the tread groove nearest the center of the tire at three locations equally spaced around the circumference of the tire….” If you look at a ruler - you will be amazed how little 1/16 of an inch is.
A tire is unsafe if it has ply or cord exposed or is marked “not for highway use,” “for racing purposes only” or “unsafe for highways use”. Additionally, if the tire tread or sidewalls have any cracks, cuts or snags deep enough to expose the body cords or was re-cut or re-grooved below the original tread design depth, the tire is considered unsafe.
Again, it is wise to keep your tires inflated to the vehicle manufacturer’s recommended tire pressure. This insures that the most tire surface is on the roadway and that the tire does not become convex or concave, again, reducing contact with the roadway.