See also:

Tread
The part of the tire that comes into contact with the road. ...

Ruts and gravel roads
Observe the following rules when driving along ruts in off-road terrain or on roads with loose gravel: Check that the ruts are not too deep and that your vehicle has sufficient clearance. ...

Checking the tire pressures
Important safety notes WARNING   Follow recommended tire inflation pressures. Do not underinflate tires. Underinflated tires wear excessively and/or unevenly, adversely affect handling ...