The "500 kilometer" marketing ploy for a 300-mile race is a trick in the book used by NASCAR since the 1970's, when Riverside (CA) switched to metric distances to cut the races.

The Nextel Cup races at Phoenix are 500k races, and the two road courses are 350k races.

Fro 1992-1997, the 311-mile races at Talladega for Busch Series cars were known as 500-kilometer races. A fan complaint led to the race distance being shortened by four laps to 300-mile races, and in 2002, Aaron's Rents restored the Metric 500 distance.

Personally, I think making the 300-mile races 500k races (eight extra laps) would be better for fans. One extra fuel stop, one pit move, or one flawed incident would change the drama -- a 300-mile loser is a 500k winner.