1966 NASCAR International Rule Book Specifications NASCAR Grand National Championship Circuit Section 20-29 -- Tires

a. No knobs, powergrip baldies, speedway treads, or worn out tires allowed. No cross grooving allowed. Standard treads only. Racing rubber permitted. For tire sizes on all models consult allowable sizes on specifications chart.

b. All four tires must be the same size as to actual measurement, and must be of the same make and the same tread design.

c. A measuring device (shown in diagram on rear pages of Rule Book) will be used to determine maximum size of tire. To obtain accurate reading, inflate tire to 60 pounds, place measuring device over tire and exert slight hand pressure.

d. Recaps must be approved by organizer, and recaps will not be permitted on any track one mile or over in size. Maximum tread width on recap tires will be 8 inches, and all four recap tires must be the same size as to actual measurements.

e. Same type tread and grade rubber must be available to all contestants.

f. Stock racing tires, with inner safety tires, compulsory on all NASCAR super-speedways and other specified tracks.