The part that the trend design of a passenger tire plays in its wet tractive ability is the most important single variable as far as the tire is concerned. This is apparent when we consider that the tire has to make contact through the wet film on the road before it can become effective. The tread design enables the tire to do this. Once the tire makes contact with the road, the tread compound and tire construction become important.The external variables that affect wet traction are also considered. These include speed, surface coefficient, load, temperature, and inflation pressure.All of these variables are discussed, with special emphasis placed on the tread design.