The photograph above illustrates the illegal and careless regrooving of truck tires - radial and bias. There is no question that the individual who regrooved this tire knew he cut into tire fabric; you experience a distinct feeling when fabric is cut or steel belt cable is hit while regrooving. 

Federal regulations mandate a minimum of 3/32" (2.4 mm) of undertread - anything less is a violation of federal regulations. 

Many of these illegally regrooved tires are found in truck stops as used tires and can be purchased from tire dealers selling used tires. 

The National Highway Traffic Safety Administration (NHTSA) has cautioned tire dealers and consumers not to purchase improperly regrooved bargain-priced tires. The caution states that a regrooved tire is a used tire that has had either its original tread pattern renewed by cutting the existing grooves deeper, or a new pattern cut into it. Regrooving is permitted only under strict federal standards and only on tires that are labeled "Regroovable" on both sidewalls by the manufacturer. 

The Safety Agency has received reports that tires which are not labeled "Regroovable" are being illegally regrooved and sold, and has warned potential used tire buyers to shop carefully. Illegally regrooved tires are unsafe and their failure in traffic can result in death and injury to motorists and pedestrians, NHTSA says. The law provides penalties of up to $1,000 per violation. 

Consumers, tire dealers and people in the regrooving business can obtain information about correct regrooving by calling the Auto Safety Hotline at (800) 424-9393. Reports about improperly regrooved tires should be directed to the Auto Safety Hotline. 

Reprinted with permission from "Tire Retreading/Repair Journal", written by Ed Wagner.