During many televised auto races, commentators irregularly say a particular driver has gone into the marbles. This means a driver has steered into a slick patch of track around the outer edges, mainly in the corners. The marbles themselves are essentially pill-shaped pieces of rubber shaved off the cars' tires as they race. Track maintenance crews use street sweepers to remove these marbles between races, but little can be done to prevent their formation through a race.

The tires used for both NASCAR and IROC-style racing are entirely different from the standard road tires on passenger cars. In order to provide maximum grip between the tires and the track, manufacturers produce wide, grooveless racing tires called slicks. Besides providing more contact area, these slick tires also use a softer form of rubber, which literally melts from the temperature of the track and the friction of driving. The surface of a race track can be very rough, but this provides additional grip for the drivers.

One problem driver's face with these soft rubber tires and the abrasive track surface is the formation of marbles. If there are 30 cars in a race, for example, this translates to 120 tires able to producing marbles. Over the course of a 500-mile race, the build-up of rubber marbles and other debris from the tires can become important. Under steering into a corner coated with marbles can mean a sudden loss of traction or even a crash into the retaining wall.