it was probably driven more by performance & load ratings

1966 HEMI B-bodies 7.75-14 Goodyear "BLUE STREAK" blue line sidewall
1967 HEMI B-bodies 7.75-14 Goodyear "HP" red line sidewall (R0/W0 ??)
1968 HEMI B-bodies F70-15 Goodyear "SPEEDWAY" red line sidewall
1969 HEMI B-bodies F70-15 Goodyear "POLYGLAS" red line sidewall (white line sidewall OPTIONAL N/C)
1970 HEMI B-bodies F70-14 Goodyear "POLYGLAS" white line sidewall (w/RWL OPTIONAL N/C) & F60-15 "POLYGLAS GT" w/RWL OPTIONAL $$
1971 HEMI B-bodies G70-14 Goodyear "POLYGLAS" w/RWL & G60-15 "POLYGLAS GT" w/RWL OPTIONAL $$