The relationship of tire tread depth to wet traction has been a subject of technical research and discussion since at least the mid 1960s. Now, nearly 50 years on, these discussions continue, and disagreements regarding the importance of improving wet traction also continue.  The research into this area is reviewed, starting from the mid-1960s, up to the most recent work (as of this writing) published in 2013.  Although there is general agreement, in the research community, regarding the importance of maintaining tread depths on passenger car tires equal to or greater than 4/32 of an inch for adequate wet-road traction, there is no such agreement in industry-recommended practice or in legislation.  In the area of tire placement, there is wide industry agreement that the best-treaded tires always should be placed on the rear of a passenger car, however a recently-published Paper (2013) disputes this conclusion.  This paper is intended to bring these issues forward and encourage their discussion.  Presented by William Blythe, President, William Blythe Inc.