Tires Tires must be able to carry your vehicle’s weight and grip the surface of the road properly. Check your tire pressure often and never drive with underinflated tires. A tire is illegal if the tread is less than one-sixteenth of an inch deep. Carry a good spare tire and check its pressure often. Inspect tires regularly for cuts, cracks, uneven wear, bald spots, bulges, and punctures. Your tires do not have as much traction on gravel or dirt roads as