I must admit to being confused by both earlier messages, but John Betmanis's email showed me a picture that helped me to understand the tire-rolling directional dilemma :
http://www.supershowevents.com/
I would summarize the 'V' issue as follows : as the tire comes up off the pavement, the tread groove should give water the opportunity to freely flow down the tire and out the sides of the tire. This allows the tire to dry for the next pavement impact.
I hope this explanation can be easily remembered by some. A less intuitive explanation might be : while riding the bike, as the rider looks down, the V should point in the direction of travel ("To look fast!")
- Don Gillies
San Diego, CA